EP3727757B1 - Setting method for expansion dowell using impact wrench - Google Patents

Description

FIELD OF THE INVENTION

The present invention relates to a setting method for expansion anchors, which is implemented as a control method for an impact wrench.

The document EP 2 985 118 A1 discloses a control method according to the preamble of claim 1.

DISCLOSURE OF THE INVENTION

A user can cancel the setting of an expansion anchor and continue after a short break. Improperly resuming tightening can damage the expansion anchor.

An embodiment of a control method of an impact wrench for setting an expansion anchor executes a first sequence with the following phases in response to actuation of a button. In a first phase, a rotary impact is repeatedly exerted on a screw element of the expansion anchor and a torque transmitted by the rotary impact to the screw head is estimated. The first phase S1 is continued until the estimated transmitted torque exceeds a threshold value specified for the expansion anchor. In a second phase, a predetermined number of rotary blows for the expansion anchor is exerted on the screw head. If the pushbutton is released before the end of the first sequence, a premature release of the pushbutton and the phase in which the pushbutton was released are stored in a memory. In response to an actuation of the button in the event of a stored premature release in the memory, a second sequence of phases is executed, the second sequence depending on the phase in which the button was previously released.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1

einen Schlagschrauber

Fig. 2

ein Eingabeelement

Fig. 3

einen Spreizanker

Fig. 4

ein Ablaufdiagramm zu dem Betriebsmodus "Spreizanker"

Fig. 5

ein Verlauf des geschätzten Drehmoments

Fig. 6

eine Schraubverbindung von zwei Stahlplatten

Fig. 7

eine Schraubverbindung von zwei Stahlplatten

Fig. 8

einen Verlauf eines Drehwinkels

Fig. 9

ein Ablaufdiagramm zu dem Betriebsmodus "Stahlbau"

Fig. 10

einen Verlauf eines Drehwinkels

Fig. 11

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

an expansion anchor

Fig. 4

a flowchart for the "expansion anchor" operating mode

Fig. 5

a course of the estimated torque

Fig. 6

a screw connection of two steel plates

Fig. 7

a screw connection of two steel plates

Fig. 8

a course of an angle of rotation

Fig. 9

a flowchart for the "steel construction" operating mode

Fig. 10

a course of an angle of rotation

Fig. 11

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 Impact wrench

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 striking 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 in steps about 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 striking mechanism 3 by way of 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 provide a continuous torque or short-term torque via the claws 12 Transferring angular momentum to the anvil 11. 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 hammer 10 transmits the kinetic energy gained in the meantime to the anvil 11 in a short pulse. One embodiment provides that the hammer 10 is forcibly 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 with a square, hollow cross-section, the dimensions of which essentially correspond to the tool holder 17. Opposite the socket, 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 operating modes include a setting process for expansion anchors and a setting process for screw connections in steel construction.

The input element 26 can contain, 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 show the expansion anchors 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, for example 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 based on an image recorded by the camera 34 , or at least limit a selection of connection types presented to the user based on the image.

Expansion anchor

Fig. 3 shows an expansible anchor 35, which in a wall 36 anchored to an attachment 37 on the wall 36 are fixed. The expansion anchor 35 has an anchor rod 38 . At one end of the anchor rod 38 there is a screw head 21 . At an end facing away from the screw head 21 , a spreading mechanism 39 is provided. The expansion mechanism 39 is inserted into a borehole in the wall 36 . A tensile stress acting on the expansion mechanism 39 by the screw head 21 converts the expansion mechanism 39 into a radial clamping force against the inner wall of the borehole. The expansion anchor 35 has a self-locking effect, since an increasing tensile load on the expansion anchor 35 due to the attachment 37 leads to a higher clamping force. Thus 35 its specified load values are guaranteed for a set expansible anchor, the expansible anchor 35 is preloaded during installation by means of the screw head 21st The expansion anchor 35 is specified with a target torque with which the screw head 21 is to be tightened when setting.

A manual setting process of the expansion anchor 35 provides the following. In a preparatory step, a borehole is drilled into the wall 36 in accordance with the specifications of the expansion anchor 35. The specification specifies, among other things, the diameter of the borehole, which is equal to the outer diameter of the expansion mechanism 39 . The expansion mechanism 39 is driven into the borehole, typically with rotary blows of a hammer. The attachment 37 is positioned on the screw head 21 . The screw head 21 is then tightened manually using a torque wrench. When tightening, the screw head 21 is supported indirectly via the attachment 37 on the wall 36 along the anchor rod 38 , whereby the tensile stress is generated. The user ends the tightening when the torque wrench signals that the specified target torque of the expansion anchor 35 has been reached. In some applications, the screw head 21 is then loosened again, for example in order to align the attachment 37. The user then tightens the screw head 21 again with the torque wrench and the same specified target torque. In other applications, several expansion anchors 35 are necessary in order to fasten the attachment 37. The user can initially pretension each of the expansion anchors 35 a little before the expansion anchors 35 are tightened according to the target torque. Furthermore, the user can be interrupted when tightening an expansion anchor 35 , whereupon the user hopefully continues the process later with the torque wrench.

The spreading mechanism 39 is based, for example, on a sleeve 40 and a cone 41 on the anchor rod 38 . The sleeve 40 is opposite the cone 41 along the anchor rod 38 movable. In the exemplary illustration, the anchor rod 38 has a thinner cylindrical neck 42 which the sleeve 40 encloses. An inner diameter of the sleeve 40 is larger than the outer diameter of the neck 42 . Adjacent to the sleeve 40 , on the side of the sleeve 40 facing away from the screw head 21 , the cone 41 is arranged. The jacket surface of the cone 41 tapers in the direction of the sleeve 40 . The outside diameter of the jacket surface decreases from a value larger than the inside diameter of the sleeve 40 to a value smaller than the inside diameter of the sleeve 40 . The specified diameter of the borehole corresponds to the outer diameter of the sleeve 40 , which is why the latter adheres or rubs against the inner wall of the borehole. When the anchor rod 38 and thus the cone 41 are tightened, the sleeve 40 remains standing while the cone 41 is pulled into the sleeve 40 . The cone 41 expands the sleeve 40 . Sleeve 40 and cone 41 can be designed in many ways. For example, the sleeve 40 can be provided with a plurality of tabs facing the cone 41. The sleeve 40 can be closed or slotted around the circumference. Furthermore, the cone 41 can be conical, corrugated, pyramidal in shape. An essential aspect for the functioning is the coefficient of friction of the sleeve 40 on the inner wall. The sleeve 40 is typically made of a steel or other iron-based material. The wall 36 is made of a mineral building material, for example concrete or natural stone.

The screw head 21 can, for example, consist of an external thread 43 on the anchor rod 38 and a nut 22 placed on the external thread 38 . The nut preferably has a hexagonal circumference. Alternatively, the anchor rod 38 can have an internal thread into which a screw is inserted. The screw has a head which projects radially beyond the anchor rod 38 . For example, the head of the screw has a hexagonal circumference.

Control method "expansion anchor"

The impact wrench 1 implements a setting method for the expansion anchor 35 ; "Expansion anchor" operating mode ( Fig. 4 ). The setting method is suitable for fastening an attachment 37 to a wall 36 with the expansion anchor 35 . In a preparatory step, the user drills the borehole into the wall 36 and pushes the expansion anchor 35 into the borehole. The screw head 21 is tightened by means of the impact wrench 1 . Compared to a continuously rotating electric screwdriver, the impact wrench 1 is distinguished by the generation of a repetitive rotary impact with short-term and therefore high torque. Furthermore, there is no rigid coupling between an output spindle 4 and a handle 7 of the impact wrench 1 , which is why a counter-torque acting back on the user is typically significantly less than the rotary impact exerted. The user selects the “expansion anchor” operating mode by means of the input element 28 and specifies the type of expansion anchor 35 .

Several control parameters are assigned to each type of expansion anchor, which are necessary for the subsequent proper sequence of the setting process. The control parameters are stored in the memory 25 for the type of expansion anchor. In response to the input or selection of the expansion anchor 35 , the control unit 24 reads out the corresponding control parameters. The control parameters are preferably retained until the user selects a different type of expansion anchor 35. It is not necessary to select the expansion anchor 35 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. A speed D of the electric motor 2 is zero or drops to zero. The separation can take place electromechanically by the button 9 itself or by an electrical switching element in the current path between the electric motor 2 and the power supply. The button 9 must be kept pressed by the user throughout the entire setting process. If the user releases the button 9 , the electric motor 2 is immediately disconnected from the power supply and, as a result, the setting process is interrupted. The impact wrench 1 preferably falls into a standby mode when the button 9 is released. In the standby mode, the impact wrench 1 reduces its energy consumption, in particular for a battery-powered impact wrench 1 . For example, the control unit 24 can be deactivated; reduce its functionality to the pure checking of the button 9 and the input element 28 , et cetera.

The setting process begins when button 9 is pressed. If necessary, the impact wrench 1 is woken up from the standby mode. In a preparatory phase, it can be checked whether the user has previously selected an expansion anchor 35 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.

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 with the impact wrench 1 due to the mechanical decoupling between the output spindle 4 and the electric motor 2. Direct measurement of the torque output by means of a sensor on the output spindle is technically very demanding due to the high mechanical loads and is not suitable for the impact wrench. The setting method makes do with a rough estimate of the torque M exerted in a first phase S1 and a subsequent correction in a second phase S2 . The two-phase method is more robust with respect to a priori unknown influences on the setting behavior, in particular the influence of the nature of the wall 36 on the setting process.

When the button 9 is pressed, a pre-phase typically begins, which is not explained further in the following description. During the preliminary phase S1 , the torque M exerted by the impact wrench 1 is so low that the impact mechanism is not triggered and the impact wrench 1 continuously exerts a typically increasing torque. The first phase S1 of the setting process begins with the first blow of the impact wrench 1 (time t0 ). A highly schematic curve 44 of the torque M is shown in FIG Fig. 5 shown. During the first phase S1 , the torque M exerted by the output spindle 4 is estimated. The first phase S1 is ended by default when the estimated torque M exceeds a threshold value M0 (C1 ). The threshold value M0 is typically less than the setpoint torque M9 for the expansion anchor 35 .

During the first phase ( S1 ), the electric motor 2 rotates the drive spindle 15 preferably at a predetermined first speed D1 . 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 determine. The first speed D1 is one of the control parameters assigned to the expansion anchor 35. 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 impact and is accelerated by the drive spindle 15 up to the next rotary impact on the anvil 11. The next rotary impact occurs when the hammer 10 is again aligned with the anvil 11. Due to the largely predetermined acceleration path, 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. The angular momentum or a variable describing the angular momentum can be determined in a series of tests for different speeds and stored in a family of characteristics.

During the first phase S1 , the 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 strokes by the angular spacing of the claws 12 , for example 180 degrees, and if the anvil 11 has rotated, it also rotates by the rotation angle δΦ of the output spindle 4 . The rotational impacts are detected by a rotational impact sensor 48. 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 rotational impact sensor 48 can, for example, the increased short-term vibration associated with the rotational impact in the Grasp impact wrench 1 . The vibration is compared, for example, with a threshold value; the beginning or the end corresponds to the point in time at which 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 torsional shock sensor 48 detects the power consumption or a speed fluctuation of the electric motor 2 . The power consumption increases briefly during the turning stroke. The angle of rotation of the drive spindle 15 can be calculated, for example, from the speed D or the signals of the rotation sensor 45 and the time span. 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 impact wrench 1 continuously compares the estimated torque M with the threshold value M0 during the first phase S1 . The first phase S1 is ended immediately when the threshold value M0 is exceeded ( C1 ). In one embodiment with the constant rotational speed D1 , the comparison of the torque M with the threshold value M0 is equivalent to a comparison of the angle of rotation per rotation beat δΦ with a threshold value per rotation beat δΦ0. A pairing of a speed D1 and an angle of rotation δΦ0, which is to be fallen below, can be stored in the memory 25 for an expansion anchor 35. The first phase S1 is ended when the screw head 21 only rotates a little. The detection of the angle of rotation δΦ is becoming increasingly imprecise. The correlation between speed and angular momentum also decreases.

The second phase S2 immediately follows the first phase S1 . The speed D of the drive spindle 15 can still be regulated to the first speed D1. During the second phase, a predetermined number N1 of rotary impacts is exerted. The number N1 of rotary impacts is another control parameter specific to the expansion anchor. The target torque M9 of the expansion anchor 35 is approximately reached with the number N1 of rotary impacts. After the first phase S1 , the angle of rotation δΦ is approximately the same for each further rotary stroke. The number N1 of rotary strokes thus corresponds to a rotation through a predetermined angle of rotation ΔΦ1. Assuming an elastic behavior of the expansion anchor 35 , the additional tensile stress of the expansion anchor 35 is largely proportional to the angle of rotation Δφ1. The tensile stress can thus be adjusted in a metered manner via the number N1 of rotary impacts. The necessary number N1 of rotary impacts or the rotation angle δΦ can be determined in test series for the expansion anchor 35 and the impact wrench 1 and the specified speed D1 of the second phase S2 and stored in the memory 25. During the second phase S2 , the number N of rotary impacts exerted is counted. Recognizing the turning strokes can, as stated above, take place, for example, by means of a rotation sensor 48. The second phase S2 is ended immediately when the number N of rotary strokes reaches the target number N1 (C2 ).

The second phase S2 is preferably followed by a relaxation phase S3 . The repetition rate of the rotary impacts is reduced compared to the second phase S2. The speed D is reduced to a second speed D2 . The second speed D2 is lower than the first speed D1 . In particular, the second speed D2 is below the critical speed which the impact wrench 1 needs to achieve the target torque. The second speed D2 is between 50% and 80% of the first speed D1, for example. The relaxation phase S3 is preferably time-controlled. A duration T1 of the relaxation phase S3 is, for example, in the range between 0.5 seconds [s] and 5 s.

The two-phase or three-phase setting method described above is suitable for tightening an expansion anchor 35 immediately after it has been inserted into the borehole. It can happen that for the subsequent alignment of the attachment part 37, the user will loosen the tensioned expansion anchor 35 and subsequently tighten it again. However, going through the two phases or three phases again could damage the expansion anchor 35 or even the subsurface.

The setting method therefore has a test routine in the “expansion anchor” operating mode, which determines at least during the first phase S1 whether the expansion anchor 35 has already been tightened. The exemplary test routine determines a rate of change w of the estimated torque M. As already described, the torque M increases from twist to twist. The rate of change w , ie the increase in torque M between successive rotary strokes or averaged over several rotary strokes, proves to be a robust characteristic which discriminates between an expansion anchor 35 that has never been tightened and an expansion anchor 35 that has been loosened again. A curve 49 of the estimated torque M for a previously released expansion anchor 35 is shown in FIG Fig. 5 shown. The rate of change w is characteristically greater in the case of the expansion anchor 35 (curve 49 ) that has been loosened again than in the other case 44 . The impact wrench 1 determines the rate of change w during the first phase S1 and compares the rate of change w with a limit value w0 . The rate of change w is preferably averaged over several rotary strokes or a time window δ T , which typically extends over several rotary strokes. If the limit value w0 is exceeded, the impact wrench 1 ends the first phase S1 . The limit value w0 is another of the control parameters which are assigned to the expansion anchor 35. The limit value w0 can be stored as a rate of change. the Rate of change w can also be detected by means of a predetermined time window Δ T and a predetermined threshold value M2 of the torque M to be reached within the time window Δ T. The time window Δ T begins with the first beat t0 . Exceeds the threshold value M, the torque M2 still within the time window Δ T the first phase is ended with S1 exceeding the threshold M2. The time window Δ T and the threshold value M2 are stored accordingly.

The first phase S1 ended prematurely in this way is followed by a modified phase S2b . The modified phase S2b is essentially the same as the second phase S2 . The impact wrench 1 exerts a predetermined number N2 of rotary impacts. The number N2 is significantly less than in the second phase S2. The number N2 is less than half the number N1 , for example less than a third of the number N1 . As a result of the modified second phase S2b , a significantly lower additional torque is exerted on the expansion anchor 35 than is the case with the standard second phase S2 . The modified second phase S2 is therefore significantly shorter than the standard second phase S2 . If a relaxation phase S3 is provided, this follows the modified second phase S2b .

In one embodiment, the rate of change w can also be monitored during the second phase S2. If the rate of change w exceeds the predefined threshold value w0 , the second phase S2 is ended prematurely and the method continues with the modified second phase S2b .

The user can intentionally or inadvertently release the button 9 during the setting process. The electric motor 2 stopped immediately or at least disconnected from the power supply. The setting procedure is thus canceled. The control method logs the setting state reached in the memory 25. In particular, it is recorded in the memory 25 which of the three phases of the setting process has been reached. The impact wrench 1 can then pass into the standby mode S0.

The control process enables the user to complete the setting process. In one embodiment, the user is requested, for example via the display 27, to complete the setting process. The user can use the input element 28 to select whether the setting process should be continued with the next actuation of the button 9 or, alternatively, a standard new setting process should take place. The request can appear, for example, when the user presses the button 9 again. Alternatively, the display 27 can permanently signal the request to the user. The user can make the request by means of the input element 28 respond. Alternatively, the button 9 can be assigned an actuation pattern to the “continue setting process” mode. For example, tapping twice before pressing the button 9 fully corresponds to the selection "continue setting process", while pressing the button 9 immediately corresponds to the selection "standard new setting process". If the user does not respond to the request within a waiting period, for example within 30 s, the control method returns to its standard operation and will carry out the next setting process in accordance with a standard new setting process.

The standard new setting process takes place after the two or three phases described above. If the user requests that the setting process be continued, the above setting procedure is modified depending on the setting status that has already been reached.

If the setting process was aborted during the first phase S1 , the setting process begins anew, ie with the first phase S1 . The torque M is estimated or the angle of rotation δΦ of each twisting stroke is determined until the termination condition for the first phase S1 is reached and whereupon the following phases follow.

If the setting process was aborted during the second phase S2 , only the missing rotary impacts are carried out. For this purpose, the control method stores the number of rotary strokes already carried out in the log. When you continue, the specified number N rotary strokes is reduced by the number of rotary strokes stored in the protocol. The relaxation phase S3 may then follow.

If the setting process was interrupted during the relaxation phase S3 , this can be shortened by the duration already carried out before the termination. For this purpose, the control method stores the already executed duration of the relaxation phase S3 in the protocol in the event of a termination. When you continue, the duration that has already been carried out is read out from the memory 25 and subtracted from the specified duration.

steel construction

Fig. 6 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 structural 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 . In the case of other screw connections, the threaded rods can already be connected to the first structural element 50.

The user inserts the threaded rods 55 through the aligned eyes 53 . Then the screw nut 56 is put on. In the case of manual fastening, the user tightens 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.

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 shutdown 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.

Control method "steel construction"

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 construction elements 50 , 51 occasionally do not lie flat on top of one another, as exemplified in FIG Fig. 7 illustrated. In a preparatory step, the user has to ensure that the construction elements 50 , 51 lie flat on top of one another in the area of the screw connection 52. For this purpose, the user can tighten one or more of the screw nuts 56 by hand. The tightening torque can remain lower than the setpoint torque M of the screw connection 52. Use of a torque wrench is optional. The user then tightens the screw connections 52 with the impact wrench 1 , which tightens the screw connections 52 up to the target torque M. If the construction elements 50 , 51 do not initially lie flat on top of one another, the impact wrench 1 aborts the setting process and indicates the missing or incomplete preparatory step to the user. For this purpose, the user selects the “steel construction” operating mode and specifies the type of screw connections 52 .

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 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 the pushbutton 9 being actuated, 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. The first phase S11 of the setting process begins with the first stroke of the striking mechanism 3 . During the first phase S11 , the torque M exerted by the output spindle 4 is estimated. The first phase S11 is ended by default when the estimated torque M exceeds a threshold value M0. The threshold value M0 is typically less than the setpoint torque M9 for the screw connection 52 . The estimation of the torque M is carried out as described in connection with phase S1, the tightening of an expansion anchor. The control parameters required for this are stored in the memory 25 for the screw connection 52.

The second phase S12 immediately follows the first phase S11 . The speed D of the drive spindle 15 can still be regulated to the target speed Do. During the second phase, a predetermined number N3 of rotary impacts is exerted. The number N3 of rotary impacts is another control parameter specific to the expansion anchor. The target torque of the screw connection 52 is approximately achieved with the number N3 of rotary impacts. The second phase S12 largely corresponds to the second phase S2 when setting an expansion anchor 35 .

The described two-phase setting method "steel construction" is suitable for tightening a screw connection 52 for connecting two steel construction elements 50 , 51 , provided that they lie flat on top of one another. During the first phase S11 , a test routine C1 is active, which estimates whether the steel structural elements 50 , 51 are lying flat on top of one another. If the test routine C1 determines that they are lying flat on top of one another, the setting process is carried out with the phases described above until the end. If the test routine denies that they are lying flat on top of one another, a protection routine S13 is carried out. The protection routine S13 can immediately abort the setting process in a simple implementation. The display 27 of the impact wrench 1 can output a corresponding indication as to why the setting process was aborted.

The test routine C11 estimates the angle of rotation Φ of the screw connection starting from the first impact (time t0 ). A curve 57 of the angle of rotation Φ over time is compared with stored control parameters for the screw connection 52 . The angle of rotation Φ is preferably averaged from several measuring points. Fig. 8 illustrates the course 57 of the Rotation angle Φ. The rotation angle Φ, which essentially increases in steps, can in practice only be detected with a high level of noise. The rate of increase of the angle of rotation Φ can be measured for each type of screw connection 52 from test series. The course is essentially determined by the elastic behavior of the screw connection 52 . The construction elements 50 , 51 - insofar as they lie flat on top of one another - have only a slight influence on the course. Indulging in not flat superposed construction elements 50, 51 is dominated by the stiffness thereof and a gap between the structural elements 50, 51, the rigidity of the overall system. The stiffness is typically reduced. With the same impact power, a greater progression of the angle of rotation Φ per time is observed. The control parameters describe an upper limit 58 which the angle of rotation Φ must not exceed during the tightening. Exceeding the upper limit 58 is recognized as lying on top of one another in a non-planar manner. The test routine causes the setting process to be aborted S13. The upper limit 58 is preferably not a fixed value, but a value that increases with time or with the number of beats. The test routine is preferably activated with the first impact at time t0. The test routine is preferably ended after a predetermined period of time Δ T , for example the test routine is ended at the end of the first phase S11 . The upper limit 58 can be determined for different screw connections 52 , in particular different diameters of the screws, by means of a series of tests.

Steel construction II

An alternative setting method "steel construction II" runs through the first phase S11 and the second phase S12 as described above. However, the number N8 of rotary strokes for the second phase S12 is not specified in advance, but is derived from the course 59 of the rotary angle Φ during the previous setting process. An estimation routine S14 compares the course 59 of the angle of rotation Φ over time t with a family of patterns 60 ( Fig. 10 ). The samples 60 are typical courses of the angle of rotation Φ determined from series of tests when tightening screw connections 52 in steel construction. The estimation routine S14 determines the pattern 60 that comes closest to the current profile 59 . The number N8 of rotary impacts for the second phase S12 is assigned to the pattern 60 in a look-up table.

Fig. 10 shows an example of a course 59 in which the construction elements 51 lie flat on top of one another. The exemplary patterns 60 have three sections: a beginning 61 , a middle 62, and an end 63 . The beginning has a linear course with a first slope. The end has a linear course with a second slope, which is less than the first slope. The center 62 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 carried out with a compensation calculation (Fit) in which the numerical values for the degrees of freedom are varied, for example using the least squares method. The patterns 60 are expediently provided for different types of screw connections 52 in a memory 25 . The user preferably enters the type via the input element 28 before tightening the screw connection 52 . The estimation routine S14 limits the adaptation to the patterns 60 associated with the selected type.

The estimation routine S14 preferably records the angle of rotation Φ over the time t , 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 point in 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. 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 S14 adapts the pattern 60 to the measurement points. For a meaningful result of the adjustment, it is preferably carried out after a minimum number of rotary strokes. It also proves to be advantageous to carry out the adaptation at the beginning of the second phase S12 , that is to say when the estimated torque M exceeds a threshold value M0. The adaptation can be carried out repeatedly, provided that the computing power of the impact wrench 1 allows this. Alternatively, the estimation routine S14 is carried out only once.

The estimation routine S14 is terminated when a deviation of the pattern 60 from the measurement points lies within a predetermined tolerance. If, after a specified number of rotary strokes or a specified duration, a deviation of the pattern is outside a tolerance or the minimum number of measuring points for the end of the pattern is not reached, an error message is output and the setting process is aborted.

The determined pattern 60 provides information about the elastic behavior of the screw connection 52 . Based on the elastic behavior, the number N8 of necessary rotary shocks for the second phase S12 can be derived. In one embodiment, values for N8 associated with the patterns 60 are stored. Instead of a look-up table, an algorithm can determine the target number N8 from the numerical values. As soon as the estimation routine S14 has determined the target number N8 of the rotational jolts for the second phase S12 , the target number N8 is established for the second phase S12 . Starting with the change from the first phase S11 to the second phase S12, the setting process counts the number of rotary impacts performed. As soon as the number N8 is reached, the setting process is ended. The start of the second phase S12 is preferably before the target number N8 is set .

The change from the first phase S11 to the second phase S12 takes place based on an estimate of the retroactive torque M. This estimate is subject to a significant measurement error. One embodiment determines, based on the pattern 60 , with which rotary stroke 64 the threshold value M0 was exceeded. The previously made change from the first phase S11 to the second phase S12 can have occurred to a different rotary stroke than the rotary stroke 64 . The estimation routine S14 can adjust the target number N8 in accordance with the deviation.

Claims (5)

1. Control method for an impact wrench (1) for setting an expansion anchor (35), which method, in response to pressing a button (9), executes a first sequence with the following phases:

   a first phase (S1), in which a rotary stroke is repeatedly exerted on a screw element of the expansion anchor (35) and a torque (M) transmitted by the rotary stroke to the screw head (21) is estimated until the estimated transmitted torque (M) exceeds a threshold value (MO) predetermined for the expansion anchor (35); and a second phase (S2), in which a number (N1) of rotary strokes predetermined for the expansion anchor (35) is exerted on the screw head (21),

   characterized in that if the pressing of the button (9) is released before the end of the first sequence, a premature release of the button (9) and the phase in which the button (9) was released are stored in a memory (25);

   which method, in response to pressing the button (9) in the event that a premature release is stored in the memory (25), executes a second sequence of phases, the second sequence depending on the phase in which the button (9) was previously released.
2. Control method according to claim 1, characterized in that, in the case of a previous release during the first phase (S2), the second sequence is the same as the first sequence, and in the case of a previous release during the second phase (S2), the second sequence begins with the second phase (S2).
3. Control method according to either claim 1 or claim 2, characterized in that when the button (9) is released during the second phase (S2), an already executed number of rotary strokes is logged, and the second phase (S2) in the second sequence is shortened by the already executed number (N2) of rotary strokes.
4. Control method according to any of the preceding claims, characterized in that a third phase (S3) follows the second phase (S2), a repetition rate of the rotary strokes in the third phase (S2) being lower than in the second phase (S2); and, in response to a release of the button (9) during the third phase (S3), the second sequence beginning with the third phase (S3).
5. Control method according to any of the preceding claims, characterized in that if a premature release is stored in the memory (25), before or when the button (9) is pressed, the user is prompted by means of a display (27) to choose between executing the first sequence or the second sequence.

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