WO2019121754A1

WO2019121754A1 - Setting method for a screw connection using an impact screwdriver

Info

Publication number: WO2019121754A1
Application number: PCT/EP2018/085610
Authority: WO
Inventors: Matthaeus ALBERDING; Dario BRALLA; Antonio Orvieto
Original assignee: Hilti Aktiengesellschaft
Priority date: 2017-12-20
Filing date: 2018-12-18
Publication date: 2019-06-27
Also published as: EP3501741A1

Abstract

The invention relates to a control method of an impact screwdriver for tightening a screw connection, which executes a sequence of consecutive phases in response to an actuation of a button. In a first phase, an impact mechanism of the impact screwdriver repeatedly exerts rotary impacts on the screw connection, and an estimation device estimates a torque transmitted from the rotary impact to the screw connection. The first phase is finished when the estimated transmitted torque exceeds a threshold value that is predefined for the expansion anchor. In a second phase, a number of rotary impacts that is predefined for the screw connection is exerted on the screw connection. During the first phase, a test routine is carried out which estimates a rotation angle (Φ) and stops the sequence when the rotation angle (Φ) exceeds an upper limit.

Description

Setting method for screw connection by means of impact wrench

FIELD OF THE INVENTION

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

DISCLOSURE OF THE INVENTION

In steel plate-shaped components are connected with a screw. The components are only limited plan to each other, whereby a normalized fastening is difficult. It is therefore intended that by hand the screw is tightened with a torque wrench. However, the user may forget about manual tightening or improper use.

One embodiment of a control method for an impact wrench for tightening a threaded fastener executes a sequence of successive phases in response to a push-button operation. In a first phase, an impact mechanism of the impact wrench repeatedly applies rotary impacts to the screw connection and an estimating device estimates a torque transmitted by the rotary impact to the screw connection. The first phase is terminated when the estimated transmitted torque exceeds a predetermined threshold for the screw connection. In a second phase, a predetermined number of turns is applied to the screw connection or the screw connection is rotated by a predetermined angle of rotation. During the first phase, a check routine is executed which estimates a rotation angle F and terminates the sequence when the rotation angle F exceeds an upper limit.

One embodiment of a control method of an impact wrench for tightening a threaded fastener executes a sequence of successive phases in response to a push-button operation. In a first phase, a striking mechanism of the impact wrench repeatedly applies rotational shocks to the screw connection, wherein the first phase is terminated when the estimated transmitted torque exceeds a predetermined threshold for the screw connection. In a second phase will a predetermined number of turns for the screw on the screw exercised. An estimation routine estimates a course of a rotation angle F over time. A pattern is fitted to the gradient and the default number is set based on the fitted pattern.

BRIEF DESCRIPTION OF THE FIGURES

The following description explains the invention with reference to exemplary embodiments and figures. In the figures show:

Fig. 1 an impact wrench

Fig. 2 is an input element

Fig. 3 is an expansion anchor

4 shows a flow chart for the operating mode "expansion anchor"

Fig. 5 is a graph of the estimated torque

Fig. 6 is a screw connection of two steel plates

Fig. 7 is a screw connection of two steel plates

8 shows a course of a rotation angle

9 is a flowchart for the operating mode "steel construction"

10 shows a course of a rotation angle

11 is a flowchart for the operating mode "steel construction"

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

EMBODIMENTS OF THE INVENTION

impact wrench

1 schematically illustrates the impact wrench 1. The impact wrench 1 has an electric motor 2, a striking 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 applies rotational impulses (rotational strokes) to the output spindle 4 with a short-term but very high torque. The output spindle 4 rotates accordingly continuously or stepwise about a working axis 5. The electric motor 2 can be powered by a battery 6 or mains powered. 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 may be rigid or secured by means of damping elements on a machine housing 8. The electric motor 2 and the striking mechanism 3 are arranged in the machine housing 8. The electric motor 2 is switched on and off by means of a button 9. The button 9 is for example arranged directly on the handle 7 and operable by the hand surrounding the handle.

The exemplary striking mechanism 3 has a hammer 10 and an anvil 11. The hammer 10 has claws 12 which rest in the direction of rotation on jaws 13 of the anvil 11. The hammer 10 may transmit continuous torque or momentary angular momentum to the anvil 11 via the jaws 12. A coil spring 14 biases the hammer 10 toward the anvil 11, thereby holding the hammer 10 in engagement with the anvil 11. If the torque exceeds the threshold, the hammer 10 shifts against the force of the coil 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 kinetic energy gained in the meantime is transmitted by the hammer 10 to the anvil 11 in a short moment. One embodiment provides that the hammer 10 is forcibly guided on a drive spindle 15 along a helical path 16. The positive guidance can be realized, for example, as a helical depression in the drive spindle 15 and a pin of the hammer 10 engaging in the depression. 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 similar tool can be plugged onto the tool holder 17. The socket 18 has a socket with a square hollow cross-section, which substantially corresponds in its dimensions to the tool holder 17. The socket opposite the socket 18 has a mouth 20 for receiving the screw head 21, ie the hexagonal nut 22 or an analog screw. The socket 18 may be secured by means of a tool lock 23 on the output spindle 4. The tool lock 23 is based for example on a pin which is inserted through both 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 may be realized, for example, by a microprocessor and an external or integrated memory 25. Instead of a microprocessor, the control unit can be realized 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 according to the selected operating mode. The control sequences of the various operating modes may be stored in the memory 25. The operating modes include, among other things, a setting method for expansion anchors and setting methods for screw connections in steel construction.

The input element 26 may 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, if appropriate, associated connection types. The user can select the operating mode by means of the input key 28. In addition, the user can enter specifications such as size, diameter, length, setpoint 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 may be, for example, a mobile phone, a laptop or analogue mobile device. Furthermore, the input element may be an additional module which can be arranged as an adapter between impact wrench 1 and battery 6. In an application executed on the input element 30, a plurality of connection types are stored or the application can query them via a mobile radio interface from a server. The external input element 30 may represent the expansion anchors or relevant information of the connection type on a display 31. The user selects a connection type via an input key 32 or a touch-sensitive display 31. The external input element 30 transmits the type designation or parameters of the selected connection type relevant to the control method 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, eg using a Bluetooth standard. As an addition or alternative, the internal input element 28 or the external input element 30 may be provided with a camera 34 which can detect a bar code on a packaging of the type of connection. The input element 28 determines the connection type based on the detected bar code and that in the memory 25 deposited bar codes. Instead of a camera 34, a laser-based bar code reader, an RFID reader, etc. may be used to detect a label on the package or on the type of connection. In a further embodiment, an image processing in the input element 28 can recognize the connection type based on an image captured by the camera 34, or at least delimit a selection of connection types presented to the user based on the image.

expansion anchor

Fig. 3 shows an expansion anchor 35 which anchored in a wall 36 attaches an attachment 37 to the wall 36. The expansion anchor 35 has an anchor rod 38. At one end of the anchor rod 38 is a screw head 21. At a screw head 21 remote from the end of a spreading mechanism 39 is provided. The spreading mechanism 39 is inserted into a borehole in the wall 36. A tensile stress acting on the spreading mechanism 39 by the screw head 21 is translated by the spreading mechanism 39 into a radial clamping force against the inner wall of the borehole. The expansion anchor 35 acts self-locking, since an increasing tensile load on the expansion anchor 35 through the attachment 37 leads to a higher clamping force. In order to ensure its specified load values with a set expansion anchor 35, the expansion anchor 35 is pretensioned during setting by means of the screw head 21. The expansion anchor 35 is specified with a desired torque with which the screw head 21 is to be tightened when setting.

A manual setting operation of the expansion anchor 35 provides the following. In a preparatory step, a borehole is drilled in the wall 36 according to the specifications of the expansion anchor 35. Among other things, the specification specifies the diameter of the borehole, which is equal to the outer diameter of the spreading mechanism 39. The spreading mechanism 39 is driven into the borehole, typically with hammer strokes. The attachment 37 is positioned on the screw head 21. Subsequently, the screw head 21 is tightened manually by means of 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 tension is generated. The user stops 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 released again, for example, to align the attachment 37. The user subsequently tightens the screw head 21 again with the torque wrench and the same specified setpoint torque. In other applications, multiple expansion anchors 35 are necessary to secure the attachment 37. The user may first bias each of the expansion anchors 35 slightly before the expansion anchors 35 are attracted to the target torque accordingly. Furthermore, the user can be interrupted when tightening a Spreizankers 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 surrounds the sleeve 40. An inner diameter of the sleeve 40 is greater than the outer diameter of the neck 42. Adjacent to the sleeve 40, on the side remote from the screw head 21 side of the sleeve 40, the cone 41 is arranged. The lateral surface of the cone 41 tapers in the direction of the sleeve 40. The outer diameter of the lateral surface decreases from a value greater than the inner diameter of the sleeve 40 to a value less than the inner diameter of the sleeve 40. The specified diameter of the borehole corresponds to the outer diameter of the Sleeve 40, which is why this adheres or rubs against the inner wall of the borehole. When tightened on the anchor rod 38 and thus on the cone 41, the sleeve 40 stops, while the cone 41 is pulled into the sleeve 40. The cone 41 expands the sleeve 40. Sleeve 40 and cone 41 can be configured in many ways. For example, the sleeve 40 may be provided with a plurality of the cone 41 facing tabs. The sleeve 40 may be circumferentially closed or slotted. Further, the cone 41 may be conical, wavy, pyramid-shaped. An essential aspect of the operation 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 construction material, eg concrete or natural stone. By way of example, the screw head 21 can consist of an external thread 43 on the anchor rod 38 and a nut 22 mounted on the external thread 38. The nut preferably has a hexagonal circumference. Alternatively, the anchor rod 38 may have an internal thread into which a screw is inserted. The screw has a head which protrudes 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; Operating mode "expansion anchor" (Fig. 4). The setting method is suitable with the expansion anchor 35 to attach an attachment 37 to a wall 36. In a preparatory step, the user drills the wellbore into the wall 36 and pushes the expansion anchor 35 into the wellbore. The tightening of the screw head 21 by means of the impact wrench 1. Compared with a continuously rotating electric screwdriver, the impact wrench 1 is characterized by generating a repetitive rotary with short-term and 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 retro-active counter-torque on the user is typically significantly lower than the applied rotary impact. The user selects the operating mode "expansion anchor" by means of the input element 28 and indicates the type of the expansion anchor 35.

Each type of expansion anchor is assigned several control parameters, which are necessary for the subsequent proper course of the setting process. The control parameters are stored in the memory 25 to 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 maintained until the user selects another type of expansion anchor 35. Selecting the expansion anchor 35 before each setting is not necessary.

In an unactuated button 9, the electric motor 2 from the power supply, for example, the battery 6, separated. A speed D of the electric motor 2 is zero or drops to zero. The separation can be done 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 continuously by the user during the entire setting process. If the user releases the button 9, the electric motor 2 is immediately disconnected from the power supply and consequently the setting process is interrupted. The impact wrench 1 preferably falls when releasing the button 9 in a standby mode (standby). 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 mere inspection of the button 9 and the input element 28 et cetera. By pressing the button 9, the setting process begins. If necessary, the impact wrench 1 is awakened from 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 in a continuously rotating screwdriver the output torque can be measured quite simply on the power consumption of the electric motor and the speed of the output spindle, this is not possible due to the mechanical decoupling between the output spindle 4 and the electric motor 2 in the impact wrench 1. A 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 not suitable for the impact wrench. The setting process is accomplished with a rough estimate of the applied torque M in a first phase S1 and a subsequent correction in a second phase S2. The two-phase method is more robust against a priori unknown influences on the setting behavior, in particular the influence of the condition of the wall 36 on the setting process.

By pressing the button 9 typically begins a pre-phase, which will not be explained in the following description. During the pre-phase S1, the torque M exerted by the impact wrench 1 will be so small that the impact mechanism will not deploy and the impact wrench 1 will continue to apply a typically increasing torque. The first phase S1 of the setting process begins with the first stroke of impact wrench 1 (time t0). A highly schematic profile 44 of the torque M is shown in FIG. 5. During the first phase S1, the torque M exerted by the output spindle 4 is estimated. The first phase S1 is terminated by default when the estimated torque M exceeds a threshold MO (C1). The threshold value MO is typically lower 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, the rotational speed D of the drive spindle 15 directly with a rotary sensor 45 on the drive spindle 15 or indirectly via a rotary sensor on the electric motor. 2 determine. The first rotational speed D1 is one of the control parameters associated with the expansion anchor 35. The speed has an influence on the output from the impact wrench 1 torque. The hammer 10 detaches from the anvil 11 after a rotational stroke and is accelerated by the drive spindle 15 until the next rotary impact on the anvil 11. The next twist occurs when the hammer 10 is again aligned with the anvil 11. Due to the largely predetermined acceleration distance results in a higher speed of the drive spindle 15 in a higher angular velocity and a higher angular momentum of the hammer 10 in the rotary impact. In 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 during a rotary impact. In test series, the angular momentum or a variable describing the angular momentum can be determined for different rotational speeds and stored in a characteristic field.

During the first phase S1, the angle of rotation dF, by which the output spindle 4 rotates due to the rotary stroke, is determined. The output torque M corresponds to the transmitted angular momentum and the angle of rotation dF, about which the output spindle 4 rotates due to the rotation. Based on the determined rotational angle dF and the approximate correlation of angular momentum and rotational speed D, the output torque M is estimated. In the memory 25, for example, a characteristic field can be stored, which assigns a pairing of speed D and rotation angle dF torque M or a torque describing size.

The angle of rotation dF is determined by a sensor 46 in the impact wrench 1. The sensor 46, for example, directly detect the rotational movement of the output spindle 4 with a rotation sensor 47. The rotation sensor 47 can detect marks on the output spindle 4 inductively or optically. Alternatively or additionally, the sensor 46 may estimate the rotational angle dF of the output spindle 4 based on the rotational movement of the drive spindle 15 between two consecutive rotational strokes. The drive spindle 15 rotates between the two rotational strokes by the angular distance of the claws 12, for example 180 degrees, and if the anvil 11 has rotated, in addition to the rotation angle dF of the output spindle 4. The rotational shocks are detected by a rotary impact sensor 48. For this purpose, the sensor 46 detects the angle of rotation of the drive spindle 15 in the time span between two directly successive rotational strokes. The beginning and the end of the period are detected by detecting the rotational strokes by means of a rotary impact sensor 48. The rotary impact sensor 48 may, for example, the increased short-term vibration associated with the rotational shock in the Capture impact wrench 1. The vibration is compared, for example, with a threshold, the beginning or the end corresponds to the time of exceeding the threshold. The torque sensor 48 may also be based on an acoustic microphone or infrasonic microphone that detects a peak in volume. Another variant of a rotary speed sensor 48 detects the power consumption or a rotational speed fluctuation of the electric motor 2. The power consumption rises briefly during the rotary impact. The angle of rotation of the drive spindle 15 can be calculated, for example, from the rotational speed D or the signals of the rotary sensor 45 and the time span. The rotational angle dF of the output spindle 4 is determined as the rotational angle of the drive spindle 15 minus the angular distance of the claws 12.

The impact wrench 1 continuously compares the estimated torque M with the threshold value MO during the first phase S1. The first phase S1 is terminated immediately when the threshold MO is exceeded (C1). In an embodiment with the constant rotational speed D1, the comparison of the torque M with the threshold value MO is equivalent to a comparison of the rotational angle per rotational speed dF with a threshold value per rotational speed dFO. In the memory 25, a pairing of a rotational speed D1 and a rotational angle dFO to be undershot can be stored for an expansion anchor 35. The first phase S1 is terminated when the screw head 21 only turns a little. The detection of the rotation angle dF becomes increasingly inaccurate. Likewise, the correlation between speed and angular momentum decreases.

The first phase S1 is immediately followed by the second phase S2. The speed D of the drive spindle 15 may continue to be regulated to the first speed D1. During the second phase, a predetermined number N1 of turns are applied. The number N1 of the rotary impacts is another control parameter specific to the expansion anchor. With the number N1 of the rotational strokes, the setpoint torque M9 of the expansion anchor 35 is approximately achieved. After the first phase S1, the angle of rotation dF is approximately the same for each additional rotary stroke. The number N1 of the rotary strokes thus corresponds to a rotation about a predetermined angle of rotation DF1. 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 DF1. The tensile stress can thus be adjusted in doses over the number N1 of the rotational strokes. The necessary number N1 of rotational strokes or the rotational angle dF can be determined in test series for the expansion anchor 35 and the impact wrench 1 and the predetermined rotational speed D1 of the second phase S2 and stored in the memory 25. During the second phase S2, the number N of strokes is counted. The recognition of the punches can be carried out as described above, for example by means of a rotary impact sensor 48. The second phase S2 is terminated immediately when the number N of turns reaches the target number N1 (C2).

The second phase S2 is preferably followed by a relaxation phase S3. The repetition rate of the rotational shocks is reduced compared to the second phase S2. The speed D is lowered to a second speed D2. The second speed D2 is less than the first speed D1. In particular, the second speed D2 is below the critical speed which the impact wrench 1 requires to reach the setpoint torque. The second rotational speed D2 is for example between 50% and 80% of the first rotational speed D1. 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 above-described two-phase or three-phase setting method is suitable for attracting an expansion anchor 35 immediately after it has been inserted into the borehole. It can occur that for the subsequent alignment of the attachment 37, the user will solve the strained expansion anchor 35 and subsequently tighten again. However, a repeated passage through the two phases or three phases could damage the expansion anchor 35 or even the ground.

Therefore, in the operating mode "expansion anchor", the setting process has a check routine which determines, at least during the first phase S1, whether the expansion anchor 35 has already been tightened once. The exemplary test routine determines a rate of change w of the estimated torque M. As previously described, the torque M increases from rotary to rotary. The rate of change w, ie the increase of the torque M between successive laps or averaged over several lashes, proves to be a robust characteristic which discriminates between a never tightened expansion anchor 35 and a newly released expansion anchor 35. A plot 49 of the estimated torque M for a previously released expansion anchor 35 is shown in FIG. The rate of change w is characteristically greater in the case of the once again released expansion anchor 35 (profile 49) than in the other case 44. 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 a plurality of spins or a time window t, which typically extends over a plurality of spins. If the limit value wO is exceeded, the impact wrench 1 ends the first phase S1. The limit value w0 is another of the control parameters associated with the expansion anchor 35. The limit value wO can be stored as a rate of change. The Rate of change w can also be detected by means of a predetermined time window DT and a predetermined threshold value M2 of the torque M to be reached within the time window DT. The time window DT starts with the first beat t0. If the torque M exceeds the threshold value M2 within the time window DT, the first phase S1 is ended when the threshold value M2 is exceeded. Accordingly, the time window DT and the threshold value M2 are stored.

The so prematurely ended first phase S1 is followed by a modified phase S2b. The modified phase S2b is substantially equal to the second phase S2. The impact wrench 1 exerts a predetermined number N2 of turns. The number N2 is significantly lower than in the second phase S2. The number N2 is less than half the number N1, e.g. less than a third of the number N1. By the modified second phase S2b a significantly lower additional torque is applied to the expansion anchor 35, as is the case in the standard second phase S2. The modified second phase S2 is thus significantly shorter than the standard second phase S2. As far as a relaxation phase S3 is provided, this connects to 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 predetermined threshold w0, the second phase S2 is terminated prematurely and the method continues with the modified second phase S2b.

The user may intentionally or accidentally release the button 9 during the setting process. The electric motor 2 stopped immediately or at least disconnected from the power supply. The setting process is thus aborted. The control method logs in the memory 25 the achieved set state. In particular, it is recorded in the memory 25 which of the three phases of the setting process has been reached. Thereafter, the impact wrench 1 can go into the standby mode SO.

The control method allows the user to complete the setting process. In one embodiment, the user is prompted for example via the display 27 to complete the setting process. The user can select by means of the input element 28 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 may appear, for example, when the user presses the button 9 again. Alternatively, the display 27 may permanently signal the prompt to the user. The user can request by means of the input element 28 answer. Alternatively, the mode "continue setting process" the button 9 an operating pattern be assigned. For example, a double tap before completely pressing the button 9 corresponds to the selection "continue setting", while the immediate pressing of the button 9 corresponds to the selection "standard new setting". If the user does not respond to the request within a waiting period, eg, within 30 seconds, the control process returns to its default mode and will perform the next set operation according to a standard new setting procedure.

The default new setting process is after the two or three phases described above. If the user requests a continuation of the setting process, the above setting method is modified depending on the setting status already reached.

If setting was aborted during the first phase S1, the setting process starts from new, i. with the first phase S1. The torque M is estimated or the rotational angle dF of each rotary stroke determined until the termination condition for the first phase S1 is reached and followed by the subsequent phases.

If the setting process was aborted during the second phase S2, only the missing beats are executed. For this purpose, the control method stores in the log the number of already executed drafts. When continuing, the predetermined number N of laps is reduced by the number of laps stored in the log. The relaxation phase S3 optionally follows.

If the setting process was interrupted during the relaxation phase S3, this can be shortened by the already executed duration before the termination. For this purpose, the control method stores in the protocol the already executed duration of the relaxation phase S3 in the event of an abort. When continuing, the already executed duration is read from the memory 25 and deducted from the predetermined 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 resiliently by means of one or more screw 52. The structural members 50, 51 may 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 in their representation to their contacting plate-shaped sections. One or more eyes 53 are provided in the sections. The eyes 53 of the two construction elements are aligned with each other by the user.

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

The user inserts the threaded rods 55 through the aligned eyes 53. Subsequently, the nut 56 is placed. For a manual attachment, the user will tighten the nut 56 with a torque wrench until a specified torque specified for the screw connection is achieved. The specification is specified by the manufacturer of the bolted joint or specified in relevant steel construction standards. The setpoint torque ensures that the screw connection can not come loose under load, in particular vibrations. On the other hand, the threaded rod 55 should not be unnecessarily stressed, or in the worst case during the tightening of the nut 56 permanently damaged.

Torque wrench tightening 52 is a reliable and robust process, but the process is labor intensive. Especially as often the screw 52 typically includes many screws. The screw 52 could basically be tightened with a classic electric screwdriver and a corresponding shutdown until reaching the desired torque. However, the user can not afford the necessary holding force for the target torque and there is a significant risk of injury to the user. Control method "Steel construction

The impact driver 1 implements a robust setting method for the screw connection 52. The user aligns the construction elements 51 to each other, inserts the threaded rods 55 through the second construction elements 51 and sets the nuts 56 on. The construction elements 50, 51 occasionally do not lie flat against each other, as illustrated by way of example in FIG. 7. In a preparatory step, the user has to ensure that the construction elements 50, 51 lie flat on one another in the area of the screw connection 52. For this purpose, the user can tighten one or more of the nuts 56 by hand. The tightening torque may be less than the desired torque M of the screw 52 remain. Using a torque wrench is optional. Subsequently, the user pulls the screw 52 with the impact wrench 1, which attracts the screw 52 to the target torque M. If initially the construction elements 50,

51 does not lie flat on top of each other, the impact wrench 1 breaks off the setting process and alerts the user to the missing or incomplete preparatory step. For this purpose, the user selects the operating mode "steel construction" and specifies the type of screw connections 52.

Each type of screw 52 is associated with several control parameters, which are necessary for the subsequent proper sequence of the setting process. The control parameters are stored in the memory 25 to the type. In response to the input or selection of the threaded connection 52, the control unit 24 reads out the corresponding control parameters. The control parameters are preferably maintained until the user selects another type of threaded connection 52. Selecting the screw connection

52 before each single setting is not necessary.

In an unactuated button 9, the electric motor 2 from the power supply, such as the battery 6, is disconnected and does not rotate. The impact wrench 1 preferably falls when releasing the button 9 in a standby mode. By pressing the button 9, the setting process begins. 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 an 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 52 may be so low that the hammer mechanism 3 is not activated. This pre-phase will not be described further below. The first phase S11 of the setting process begins the first beat of the percussion mechanism 3. During the first phase S11, the torque M exerted by the output spindle 4 is estimated. The first phase S11 is terminated by default when the estimated torque M exceeds a threshold MO. The threshold MO is typically less than the setpoint torque M9 for the threaded connection 52. The estimation of the torque M is as described in connection with the phase S1 of tightening an expansion anchor. The necessary control parameters are stored in the memory 25 for the screw 52.

The first phase S11 is immediately followed by the second phase S12. The speed D of the drive spindle 15 can be further controlled to the target speed Do. During the second phase, a predetermined number N3 of turns are applied. The number N3 of the rotary impacts is another control parameter specific to the expansion anchor. With the number N3 of the rotational strokes, the nominal torque of the screw 52 is approximately achieved. The second phase S12 is largely the same as the second phase S2 when setting an expansion anchor 35. Instead of counting the number of rotational strikes N3, an angle of rotation about which the threaded connection 52, typically the nut 56, is rotated, can be estimated. The second phase S12 is terminated when a predetermined rotation angle is exceeded.

The described two-phase setting method "steel construction" is suitable to tighten a screw 52 for connecting two steel construction elements 50, 51, if they lie flat on one another. During the first phase S11, a test routine C1 is active, which estimates whether the steel construction elements 50, 51 are flat on top of each other. If the check routine C1 detects a plan-lying, the setting process is performed with the phases described above to the end. If the check routine denies a flat relationship, a protection routine S13 is executed. The protection routine S13 can immediately abort the setting process in a simple implementation. The display 27 of the impact wrench 1 can issue a corresponding hint, which is why the setting process has been canceled. The test routine C11 estimates the angle of rotation F of the screw connection starting from the first beat (time t0). A course 57 of the angle of rotation F over time is compared with stored control parameters for the screw connection 52. The angle of rotation F is preferably averaged from a plurality of measuring points. FIG. 8 illustrates the profile 57 of the angle of rotation F. The essentially stepwise increasing angle of rotation F can in practice only be detected with a strong noise. The rate of increase of the angle of rotation F can be measured for each type of screw 52 from experimental series. The course is essentially determined by the elastic behavior of the screw 52. The construction elements 50, 51 - as far as lying flat on one another - have only a small influence on the course. With non-superimposed structural elements 50, 51, their stiffness and a gap between the structural elements 50, 51 dominate the rigidity of the overall system. The stiffness is typically reduced. For the same impact performance, a greater advance of the angle of rotation F per time is observed. The control parameters describe an upper limit 58, which must not exceed the angle of rotation F during tightening. Exceeding the upper limit 58 is recognized as a non-planar superimposition. The check routine causes a cancel S13 of the setting process. The upper limit 58 is preferably not a fixed value but a value increasing with time or with the number of beats. The check routine is preferably activated with the first beat at time t0. The check routine is preferably terminated after a predetermined time DT, for example, the check routine is terminated at the end of the first phase S11. The upper limit 58 can be determined for various screw connections 52, in particular different diameters of the screws, by means of test series.

Steel construction II

An alternative setting method "Steel Structure II" passes through the first phase S11 and the second phase S12 as described above. However, the number N8 of the rotational strokes for the second phase S12 is not predetermined, but is derived from the course 59 of the rotational angle F during the previous setting process. An estimation routine S14 compares the course 59 of the rotation angle F over time t with a set of patterns 60 (FIG. 10). The patterns 60 are typical courses of the angle of rotation F determined by test series when tightening screw connections 52 in steel construction. The estimation routine S14 determines the pattern 60 closest to the current profile 59. The pattern 60 is assigned the number N8 of the rotational strokes for the second phase S12 in a look-up table.

Fig. 10 shows an example of a course 59 in which the construction elements 51 lie flat on one another. The example 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 monotonically decreasing slope. Alternatively, the center may be described by other functions with 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 curve with the pattern can be done with a fit calculation in which the numerical values for the degrees of freedom are varied, e.g. using the least squares method. The patterns 60 are conveniently 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 52. The estimation routine S14 limits the adaptation to the pattern 60 associated with the selected type.

The estimation routine S14 preferably records the rotation angle F over the time t, starting with the first impact tO, in order to obtain measurement points for the comparison. A measuring point includes the measured angle of rotation F and the associated time t. The angle of rotation F can be estimated based on the angle of rotation of the drive spindle 15 between successive turns. A time recording can be approximated by a chronological recording of the rotation angle F. 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 adaptation, this is preferably carried out after a minimum number of lashes. It also proves to be advantageous to perform the adaptation at the beginning of the second phase S12, ie when the estimated torque M exceeds a threshold value MO. The adaptation can be carried out repeatedly, as long as this allows the computing power of impact wrench 1. Alternatively, the estimation routine S14 is executed only once.

The estimation routine S14 is completed when a deviation of the pattern 60 from the measurement points is within a predetermined tolerance. If a deviation of the pattern is outside of a tolerance after a predetermined number of turns or predetermined duration, or if the minimum number of measurement points for the end of the pattern is undershot, 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 rotational strikes for the second phase S12 can be derived. In one embodiment, associated values for N8 are stored for the patterns 60. Instead of a look-up table, an algorithm can determine from the numbers the set number N8. As soon as the estimation routine S14 has determined the setpoint number N8 of the rotational strokes for the second phase S12, the target number N8 for the second phase S12 is determined. The setting method counts from the change from the first phase S11 to the second phase S12, the number of applied rotary strikes. Once the number N8 is reached, the setting process is ended. The beginning of the second phase S12 is preferably before setting the desired number N8.

The change from the first phase S11 to the second phase S12 is 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 impact 64 the threshold value MO has been exceeded. The previously made change from the first phase S11 to the second phase S12 may have occurred at a different rotation than the rotary impact 64. The estimation routine S14 may adjust the target number N8 according to the deviation.

Claims

1. Control method of a impact wrench (1) for tightening a

Screw connection (52), which executes a sequence with the successive phases in response to an actuation of a button (9):

a first phase (S11) in which a striking mechanism (3) of the impact wrench (1) repeatedly applies rotational shocks to the screw connection (52) and a

Estimating means (65) estimates a torque (M) transmitted from the rotary impact on the screw connection (52), the first phase (S11) being terminated when the estimated transmitted torque (M) has a threshold value (MO) set for the expansion anchor (35) ) exceeds;

a second phase (S12) in which a predetermined number (N3) of rotational strokes on the screw connection (52) is applied to the screw connection (52) or the screw connection (52) is rotated by a predetermined angle of rotation;

characterized in that during the first phase (S11), a check routine (C1) is executed which estimates a rotation angle F and the sequence is terminated when the rotation angle F exceeds an upper limit (58).

2. Control method according to claim 1, characterized indicates that the upper limit (58) increases with the number of applied rotational shocks from the first rotary impact.

3. Control method according to claim 1 or 2, characterized indicates that a warning is issued when canceling the sequence.

4. Control method according to one of the preceding claims, characterized

indicates that the threshold value (MO), the number (N3) of rotary strikes and the upper limit (58) are read out of a memory (25) as a function of a user-selected selection of a screw connection (52).