EP2243599B1 - Impact wrench and control method for same - Google Patents

Description

FIELD OF THE INVENTION

The present invention relates to an impact wrench, in particular a tangential impact wrench, and a control method for an impact wrench.

DESCRIPTION OF THE PRIOR ART

A tangential impact wrench periodically provides, for a short time, a large tightening torque for tightening screw connections or for setting screw anchors. To a handle or a holder of the Tangentialschlagschraubers a continuous lower torque is delivered, which must counteract the user or a stand.

The tangential impact wrench is suitable for use in a variety of materials of varying hardness, for example in stone, concrete, bricks, sand-lime brick, aerated concrete. Typically, screws are used so far that the screw head rests against a substrate (workpiece). The screw must not be turned any further as this will damage the screw or the substrate. For example, the screw head can be turned off, a round hole can be cut into the ground by the screw thread or the surface can be removed by the screw thread.

The EP 1 510 394 B1 describes an automated shutdown of an impact wrench. The impact wrench monitors the applied tightening torque. If the tightening torque exceeds a threshold value to be set, a prime mover of the impact wrench is switched off.

The WO 2007/015661 A2 describes an automated shutdown of an impact wrench by measuring a rotation angle of the screw for each beat. If the angle of rotation falls below a threshold value, the screw is considered screwed in and the impact wrench is switched off.

DE 195 03 524 A1 describes a control method in which an initially output torque is kept lower than a required torque to prevent over-tightening of a screw. Subsequently, the torque is gradually increased in an iterative process.

EP 1 695 794 A2 describes an estimator which estimates torque transmitted to a screw. EP 1 595 650 A2 and EP 0 552 990 A1 reveal more screwdrivers. The known methods require a determination of a threshold, which should be either fixed or set by a craftsman. In both cases, there is a risk that the threshold value for a substrate (workpiece) is improperly set.

DISCLOSURE OF THE INVENTION

An object is to provide an impact wrench and a control method for an impact wrench, which facilitates screwing a screw or other screw into a substrate only to a desired depth.

The control method according to the invention for an impact wrench uses the following steps: setting an operating mode for a predetermined duration, wherein during the predetermined duration a drive shaft is rotated in a low speed range, it is determined whether the impact wrench strikes, and the impact wrench in a soft material operating mode in which a rotational speed of the drive shaft is maintained in the low speed range when a low speed range shock fails, and the impact driver is switched to a hard material operating mode for which the rotational speed of the drive shaft is increased to a higher speed range; when hitting in the low speed range begins.

As stated, there is a difficulty in screwing in a screw that the properties of a substrate are not known or are not sufficiently considered when setting the impact wrench. The control method described indirectly determines the properties of the ground and the torque output by the impact wrench is set based on the characteristics.

The method according to the invention determines the properties of the substrate indirectly via the behavior of the percussion mechanism. It was recognized that the onset of beating can be correlated with the properties of the subsurface. A beating occurs only when a material of the ground is sufficiently hard. The material must be the tool or tool-coupled fastener, e.g. a screw, can hold at a low torque, so that a drive of impact wrench can store rotational energy in a buffer. In impact wrenches two impactors are deflected axially against each other against a spring force, if rotation of the impactor due to the material can not be synchronized with the drive. With a sufficient deflection, the two impactors are accelerated towards each other by the spring force. Due to a design of the impactors and possibly a backdrop at least part of the kinetic energy is converted to a torque on the ground upon impact. The initial deflection takes place only if the background of the spring force can sufficiently counteract.

For a hard ground, for example, the full power can be provided, for a soft ground a low output or a low output torque can be maintained. The screw is screwed in slower according to the ground and the screwing can be stopped at the headrest without significant rewinding.

The impact wrench according to the invention comprises: a drive shaft, an output shaft, a striking mechanism, in particular a Tangentialschlagwerk that couples the drive shaft to the output shaft for transmitting torque, an evaluation device for determining whether the striking mechanism beats, and a control device for controlling a rotational speed of the drive shaft in Dependence on whether hitting is determined.

In the dependent claims embodiments of the impact mechanism and the control method are given.

One embodiment provides that independently a first rotational speed of the drive shaft of the impact wrench and a second rotational speed of an output shaft of the impact wrench are determined and a deviation of the first rotational speed from the second rotational speed is determined as a beating of the impact wrench. The first speed of the drive shaft can be measured or alternatively determined from a speed of the prime mover. During impact operation, the output shaft is only partially rotated by the output shaft, which can rotate continuously.

An embodiment provides that the beating is determined by detecting an acceleration in the direction of impact, detecting regular banging noises and / or by a contactless detection of a tangential movement of a beater of the impact wrench and determining the lower speed detecting a first rotational speed of a drive element and / or a second speed of a tool holder of the impact wrench at the onset of hitting includes.

In a development, the speed of the drive shaft is increased to a higher speed range when a strike occurs and maintained at a failure to hit the speed of the drive shaft in the low speed range. In soft materials, where no beating at low speed begins, the speed should not be increased in favor of a quick shutdown. In hard materials, the speed is increased so that the striking mechanism can provide a high torque.

An embodiment provides that the impact wrench is switched to a soft material operating mode when low speed beating fails, and that the impact wrench is switched to a hard material operating mode when low speed beating is absent. The drive shaft may be rotated for a predetermined duration in the low speed range and set for the predetermined duration of the operating mode. The determination of the operating modes can thus be made at the beginning of a screwing in, e.g. a screw, done.

The impact wrench may be a hand-held, a supported, hand-held or a stand-held, guided machine tool.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1

einen Schlagschrauber,

Fig. 2

ein Tangentialschlagwerk,

Fig. 3

einen Amboss des Tangentialschlagwerks von Fig. 2 und

Fig. 4

ein Flussdiagramm eines Steuerungsverfahrens.

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

Fig. 1

an impact wrench,

Fig. 2

a tangential impact,

Fig. 3

an anvil of the tangential impact of Fig. 2 and

Fig. 4

a flowchart of a control method.

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

EMBODIMENTS OF THE INVENTION

Embodiments of control methods for screwing are described below, by way of example for a tangential striking impact driver shown. However, the described setting methods can also be carried out with differently designed impact wrenches.

Fig. 1 schematically shows an embodiment of a impact wrench. 1

A tool holder 2 is driven by an output shaft 3. A prime mover 4 drives a drive shaft 5. The prime mover 4 may be an electric motor, a pneumatic drive, etc. It may be advantageous to interpose between the prime mover 4 and the drive shaft 5, a transmission 6 for reducing the rotational speed of the drive shaft 5. The drive shaft 5 is permanently rotated during operation about its longitudinal axis 7 in a direction of rotation 21. The speed of the prime mover 4 can be controlled by a motor controller 33. The motor controller 33 includes, for example, an inverter for a brushless electric motor serving as a prime mover 4. The speed can be set by the user via an operating element 8. In a particular embodiment can also be provided that the reduction of the transmission 6 by the motor controller 33 is adjustable.

A striking mechanism 10 couples the drive shaft 5 to the output shaft 3. According to still different situations, the drive shaft 5 can transmit its torque continuously to the output shaft 3 or torque of the drive shaft 5 serves to wind a buffer, which in periodic shocks a higher torque on the Output shaft 3 transmits.

In Fig. 2 is an exemplary impact mechanism 10 shown in longitudinal section. The impact mechanism 10 includes an anvil 11, a rotor 12, a link 13 and a return spring 14. In the striking mechanism 10, the output shaft 3 is rotatably supported to the drive shaft 5.

The anvil 11 is rotatably connected to the output shaft 3, such that a transmitted to the anvil 11 angular momentum acts on the output shaft 3. The anvil 11 has one or more projections 15. Fig. 3 shows a plan view of the anvil 11 from the perspective of the drive shaft 5. The projections 15 may have stop surfaces 16 which are oriented parallel or inclined to the longitudinal axis 7.

The rotor 12 is annular and pushed onto the drive shaft 5. The rotor 12 can, guided by the drive shaft 5, move along the longitudinal axis 7.

The link 13 is formed on the surface of the drive shaft 5. The gate 13 spirals spirally, the turn increases in the direction of rotation 21 of the drive to the anvil 11 out. The rotor 12 engages in the slot 13. As soon as the rotor 12 moves along the longitudinal axis 7 in the direction 22 to the anvil 11, the rotor 12 is forced into a rotational movement 23 relative to the drive shaft 5. Similarly, the rotor 12 is forced to move along the longitudinal axis 7 as the rotor 12 rotates relative to the drive shaft 5.

At the periphery of the rotor 12 at least one hammer 18 is arranged. The hammer 18 has a lateral abutment surface 19, which is formed in a form-fitting or at least partially positive fit to the abutment surfaces 16 of the anvil 11. The rotor 12 and the anvil 11 may mesh with each other like a dog clutch or a slip clutch via the projections 15 and the hammers 18. During the engagement, the rotor 12 can transmit its angular momentum or its torque to the anvil 11 and drive it.

The return spring 14 exerts a force on the rotor 12 in the direction 22 to the anvil 11. In an initial position of the impact wrench 1 of the rotor 12 therefore in engagement with the anvil 11th

The permanent rotation of the drive shaft 5 is transmitted via the connecting link 13 to the rotor 12. If the rotor 12 can rotate at the same speed, that is, no relative rotation to the drive shaft 5 executes, it remains in the starting position and is not forced to move along the drive shaft 5. However, in order for the rotor 12 to be able to follow the rotation, the rotor 12 must, among other things, also be able to rotate the anvil 11 against a torque applied by the ground. The torque applied by the substrate must not exceed a threshold value. The threshold value for the torque is essentially a function of the spring force of Return spring 14, against which the rotor 12 would have to be deflected, the slope of the slide 13 and possibly the inclination of the stop surfaces 16, 19. These sizes are determined by the design of the striking mechanism 10. The threshold value can be, for example, in the range of 1 Nm to 5 Nm or 2 Nm to 3 Nm.

If the ground can apply a larger torque, proposes the striking mechanism 10. In the following, a beat cycle of the impact wrench 1 is described starting from the starting position. The rotor 12 is engaged with the anvil 11. The rotor 12 is prevented by the anvil 11 from rotating synchronously with the drive shaft 5. The link 13 now forces the rotor 12 to move along the longitudinal axis 7 out of engagement with the anvil 11. When the rotor 12 is no longer engaged, the rotor 12 may rotate relative to the anvil 11 and to the drive shaft 5. The anvil 11 and the hammer 12 come here again in a relative position in which they can interlock again. The return spring 14 drives the rotor 12 back to the anvil 11. In this case, the rotor 12 is accelerated in the direction of the longitudinal axis 7. The gate 13 forces the rotor 12 in a rotational movement 23, whereby the rotor 12 receives an angular momentum. The rotational movement 23 is stopped by the lateral stop of the hammers 18 of the rotor 12 at the projections 15 of the anvil 11. The angular momentum of the rotor 12 is transmitted to the anvil 11. The system is back in the starting position and a new beating cycle begins.

During an impact cycle, the anvil 11 and the output shaft 3 rotate at a smaller angle than the rotor 12 and the drive shaft 5. The rotor 12, driven by the drive shaft 5, rotates along the guide 13 and the anvil 11 stops. When hitting the percussion mechanism 10, therefore, a speed of the drive shaft 5 differs from a speed of the output shaft 3. The speed of the drive shaft 5 may be greater than twice the speed of the output shaft 3 by more than twice. Stay the anvil 11 and the rotor 12 in non-impact operation in engagement, the drive shaft 5 and output shaft 3 are rigidly coupled. Their respective speeds are the same. An impact cycle can be discriminated from non-impact operation based on the different speeds occurring at it.

For detecting a beating an evaluation device 30 and means 31, 32 for determining the rotational speeds of the output shaft 3 and the drive shaft 5 are provided. The evaluation device 30 compares the specific rotational speeds of the output shaft 3 and the drive shaft 5. If the two rotational speeds differ, Typically, by a factor greater than two, the evaluation device 30 recognizes this as a beating operation, otherwise as a non-beating operation.

The rotational speed of the output shaft 3 is determined by a rotational speed sensor 31. The rotational speed sensor 31 may detect the rotational speed, for example optically or magnetically. An optical speed sensor can detect markings on the output shaft 3 in reflection or via a light barrier. The markings may be formed by projections, depressions, bores, color, etc. The output shaft 3 may have a non-circular cross-section, e.g. an elliptical, square or toothed cross-section. A magnetic speed sensor detects a periodically changing magnetic flux due to the rotating output shaft 3.

The speed of the drive shaft 5 can also be determined via a speed sensor 32. Alternatively, the evaluation device 30 communicates with a motor controller 33 to query or receive the current speed of the prime mover 4. The speed of the drive shaft 5 can determine the evaluation device 30 from the requested speed of the prime mover 4 and, if present, the reduction of the transmission 7.

An exemplary control method for the impact wrench 1 will be described with reference to the flow chart in FIG Fig. 4 explained.

A user operates the system switch 9 of the impact wrench 1 to screw in a screw. A sensor detects the operation of the system switch 9. A control device 40 of the impact wrench 1 is activated. In a first phase S1, the controller 40 instructs the engine controller 33 to accelerate a rotational speed N of the drive shaft 5 to a low rotational speed N1 within a low rotational speed range.

The low speed range can range from 10% to 50%, e.g. minimum 20%, maximum 40%, the nominal highest speed Nmax of the drive shaft 5 are. The low speed N1 can be fixed. Alternatively, a control element 8 may be provided which allows the user to set the low speed N1, e.g. in the range of 10% to 50% of the nominal highest speed Nmax of the drive shaft 5.

In a second phase S2, the low speed N1 of the drive shaft 5 is maintained for a predetermined period of time T1. A screw or anchor will be used during the Time T1 at low speed N1 screwed. The time period T1 can be measured in seconds, or set indirectly over a number of turns of the anvil 11 or a screwing depth.

During or subsequent to the second phase S2, it is checked whether the impact mechanism 10 strikes or fails (S3). For this purpose, the low speed N1 of the drive shaft 5 can be compared with a speed M of the output shaft 3. The rotational speed M can be determined during or subsequently to the second phase S2. If the two speeds are different, then there is a beating operation. The evaluation of the rotational speeds and the checking whether a beating or non-beating operation is present can be carried out by the evaluation device 30. Alternatively, the presence of a beating can be determined on the basis of beating noises, typical beating acceleration values, etc.

The second phase S2 can also be ended before the expiration of the period T1, if hitting is already detected. The evaluation device 30 can transmit a corresponding trigger signal to the control device 40 for terminating the second phase S2.

If hitting is detected during the second phase S2, the evaluation device 30 instructs the control device 40 to control the percussion mechanism 10 via the prime mover 4 in accordance with a procedure for a hard surface (S4). Otherwise, the control device is to control the percussion mechanism 10 in accordance with a sequence for a soft background (S5). The two processes S4, S5 are shown below.

The sequence for a soft material S5 initially provides in a third phase S6 to leave the rotational speed N of the drive shaft 5 at the low rotational speed N1. The exemplary screw is thus only screwed.

In one embodiment, the evaluation device 30 monitors whether hitting occurs during the third phase S6 (S7). For example, a subsurface may exert a higher torque on the anvil 11 due to a more deeply screwed or harder layers below the surface.

If a beating is detected, the evaluation device 30 instructs the control device 40 to increase the rotational speed to a middle rotational speed N2 in the middle rotational speed range in a fourth phase S8. The middle speed range can For example, be between 35% to 75% of the nominal maximum speed Nmax, eg minimum 50%, maximum 60%. The low speed N1 may differ from the average speed N2 by a factor of 2 to 10, eg 2 to 3.

In the fourth phase S8, furthermore, the evaluation device 30 can monitor the impact behavior. Once suspension of beating is detected, the evaluation device 30 may instruct the controller 40 to drive the hammer mechanism again according to the third phase S6.

A shutdown of the prime mover 4 takes place from the third phase S6 and the fourth phase S8, when the screw is detected as being screwed. This can be done by a variety of methods. For example, the rotational speed N of the drive shaft 5 or the rotational speed of the M of the output shaft 3 can be monitored. In the monitoring, an expected speed Navg or Mavg is determined, which can be, for example, as an average in a past interval of occurring speeds. As soon as the screw is screwed in and the head rests, the torque to be applied increases abruptly. As a result, the speed N or M breaks. Upon detection of such a drop of about 20% to 50% of the current speed N or M with respect to the expected speed Navg or Mavg, the prime mover 4 is deactivated.

The process for a hard material S4 provides a fifth phase S9. The rotational speed of the drive shaft 5 is accelerated to a high rotational speed N3 in a high rotational speed range. The high speed range is between 50% and 100% of the nominal highest speed Nmax, e.g. minimal 75%. The controller 40 controls the hammer mechanism 10 to output a maximum torque.

In one embodiment, the evaluation device 30 continues to monitor whether the beating stops (S10). If the beating stops, the controller 40 changes to the second phase S2. At the low speed N1 can be checked again whether the screw has penetrated into a soft material.

A switch-off from the fourth phase S9 can take place as a function of the development of the rotational speed M of the output shaft 3. The speed of the output shaft 3 is a measure of the torque that must be applied to rotate the screw. The higher the required torque, the smaller the angle, the output shaft 3 can be rotated with each beat. If the speed M changes faster than a predetermined rate of change and / or the speed changes faster than a mean detected Change rate Mavg, the prime mover 4 is stopped. It is assumed that the change is effected on a support of the screw head on the ground. The rate of change describes the change in speed over time. This can be recorded and its mean value determined.

In a further embodiment, a sixth phase S11 is provided, is changed to, if the speed M of the output shaft 3 falls below a lower threshold Mmin. The sixth phase S11 is provided in the event that the impact wrench 1 is operated at its load limit. The speed is increased to the highest possible speed Nmax, N4. The sixth phase S11 also differs from the fifth phase S9 by the turn-off behavior. Instead of a comparison of the previous behavior of the speed Mavg or Navg, the prime mover 4 is turned off as soon as the speed M of the output shaft 3 falls below a second lower threshold. Alternatively, the prime mover 4 can be turned off when the lower threshold value Mmin remains below for a predetermined period of time after the rotational speed has been increased to Nmax.

In Fig. 4 are to keep the flow chart clear, the stop conditions for a shutdown of the prime mover are not shown. These can be preceded in a design all other functions vorranging to ensure a quick shutdown.

A further development provides for a boost function. After switching off the prime mover 4, the position of the operating switch 9 is monitored. If the operating switch 9 is kept depressed for a predetermined period of time, the primary drive 4 is reactivated according to the first phase S1. The controller 40 starts anew with the procedure of one of the preceding embodiments.

Another embodiment provides error detection. If a screw is turned over, the torque which the screw of the drive shaft 3 counteracts decreases. The speed of the drive shaft 3 increases, at least in beating operation. The evaluation device 30 can monitor the speed and output a warning message when the speed of the drive shaft 3 increases. The warning message can be transmitted to a display element 41 for visualization to a user. The display element can give a visual or audible warning.

In the previous embodiments, to determine whether a beating operation or non-impact operation is present, reference has been made to the evaluation of the rotational speeds of the output and drive shafts 3, 5. Alternatively or additionally, impact noises, accelerations in the axial direction and an axial movement of the rotor 12 can be used for the evaluation. For this purpose, a corresponding sensor 50 may be provided.

The speed sensors 31, 32 can detect the rotational speeds analog or digital. The evaluation device 30 may include an analog comparison stage for comparing the rotational speeds of the drive shaft 5 and the output shaft 3.

Claims (7)

1. Control method for an impact driver (1) characterised by the steps:
   setting an operating mode during a predetermined time period, wherein a drive shaft (5) is rotated in a low rotational speed range during the predetermined time period and it is determined whether the impact driver (1) is striking and, if striking does not occur in the low rotational speed range, the impact driver (1) is switched to an operating mode for a soft material in which a rotational speed of the drive shaft (5) is maintained in the low rotational speed range and, if striking commences in the low rotational speed range, the impact driver (1) is switched to an operating mode for a hard material, for which the rotational speed of the drive shaft (5) is increased to a higher rotational speed range.
2. Control method according to Claim 1, characterised in that a first rotational speed of the drive shaft (5) of the impact driver (1) and a second rotational speed of an output shaft (3) of the impact driver (1) are determined independently, and a deviation of the first rotational speed from the second rotational speed is registered as striking of the impact driver (1).
3. Control method according to Claim 1 or 2, characterised in that an acceleration in the striking direction, regular impact sounds and/or a tangential movement of a striking body of the impact driver is/are detected in order to determine that the impact driver is striking.
4. Control method according to Claim 1, characterised in that the predetermined time period begins with an actuation of a system switch of the impact driver, or with attainment of a reference rotational speed within the low rotational speed range.
5. Impact driver, comprising:

   a drive shaft (5),

   an output shaft (3),

   a striking mechanism (10), in particular a tangential striking mechanism,

   which couples the drive shaft (5) to the output shaft (3) in order to transmit a torque,

   characterised by

   an evaluation device (30) for determining whether the striking mechanism (10) is striking and a control device (40) for setting an operating mode during a predetermined time period by means of rotation of the drive shaft (5) in a low rotational speed range and in response to a determination by the evaluation device (30) whether the impact driver (1) is striking, wherein an operating mode for a soft material, with a rotational speed of the drive shaft (5) in the low rotational speed range, is set if striking does not occur in the low rotational speed range, or an operating mode for a hard material, with a rotational speed of the drive shaft (5) in a higher rotational speed range, is set if striking commences in the low rotational speed range.
6. Impact driver according to Claim 5, characterised by:

   a first rotational speed sensor (32) for capturing a rotational speed of the drive shaft (5) or of a motor (4), and

   a second rotational speed sensor (31) for capturing a rotational speed of the output shaft (3), wherein

   the evaluation device (30) compares the two rotational speeds in order to determine whether striking is taking place.
7. Impact driver according to Claim 5 or 6, characterised by:
   an impact sensor (50) for detecting striking, the impact sensor (50) including an acceleration sensor for detecting an acceleration in the striking direction, a sound transducer for detecting regular impact sounds and/or a motion sensor for contactlessy detecting a tangential movement of a striker of the impact driver (1).

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