EP4438230A1 - Impact wrench and method of controlling same - Google Patents

Abstract

An impact wrench (10) comprising a tool holder (14) attached to a drive shaft (28) for holding a tool, in particular a screwing tool, wherein the drive shaft (28) can be set in a tangentially striking movement by means of a rotary impact drive (22) drivable via a drive (24), and wherein the rotary impact drive (22) has an anvil (32) assigned to the drive shaft (28), a hammer (30) and a spring element (34) acting on the hammer (30), wherein the drive (24) is operatively connected to the hammer (30) via a guide slot (35) and wherein the impact wrench (10) has a control (36) for controlling (36) the drive based on an input measured value (ϕ), is characterized in that a state of the spring element (34) is determined as the input measured value (ϕ) and that the drive (24) is controlled depending on the state of the spring element (34). which enables particularly comfortable working with the impact wrench (10). Furthermore, the invention relates to a method (1000) for controlling an impact wrench (10).

Description

The invention relates to a machine tool with a rotary impact drive, in particular an impact wrench. The impact wrench comprises a tool holder attached to a drive shaft for holding a tool. The tool can be a screwing tool, for example. The drive shaft can be set in an at least partially tangential impact movement by means of a rotary impact drive that can be driven by a drive. The rotary impact drive has an anvil assigned to the drive shaft, a hammer and a spring element acting on the hammer. The drive is operatively connected to the hammer via a guide slot. The impact wrench also has a control for controlling the drive. The behavior of the rotary impact drive can be controlled by controlling the drive.

In order to achieve the most complete transfer of momentum from the hammer to the anvil and to avoid vibrations, the hammer should strike the anvil as tangentially as possible. However, depending on how the impact wrench is used by a user, for example depending on which tool is mounted in the tool holder, the type of workpiece to be processed by the tool, etc., misfires can occur in which the hammer does not strike the anvil at least completely tangentially.

For example, it can hit the anvil axially, i.e. parallel to the drive shaft. In such a case, considerable vibrations can be triggered. The effective power of the impact wrench transferred to the tool holder can also be significantly reduced.

In order to be able to use the impact wrench as versatilely as possible, especially in different usage situations, it would be desirable if the impact wrench had a high performance on its tool holder in as many usage situations as possible. Vibrations during operation of the impact wrench should be avoided as far as possible.

However, the specific usage situation cannot normally be easily determined by the impact wrench, so that the control system cannot rely on input parameters that directly describe the usage situation.

The object of the present invention is therefore to offer an impact wrench and a method for controlling an impact wrench, which enable rapid and comfortable, in particular low-vibration, work in different usage situations.

The object is achieved by an impact wrench, comprising a tool holder attached to a drive shaft for holding a tool, in particular a screwing tool, wherein the drive shaft can be set in a tangentially striking movement by means of a rotary impact drive drivable via a drive, and wherein the rotary impact drive has an anvil assigned to the drive shaft, a hammer and a spring element acting on the hammer, wherein the drive is operatively connected to the hammer via a guide slot and wherein the impact wrench has a control for controlling the drive based on an input measured value, wherein the input measured value corresponds to a state of the spring element.

An underlying idea is that comfortable, and especially fast, work is possible if the tool holder can be driven with as high a torque as possible. For this to happen, all blows of the hammer on the anvil should be tangential. In this case, there would be no or only very slight vibrations in the axial direction. Theoretically, the point of impact of the hammer on the anvil could be determined repeatedly and the drive could then be controlled by the control system depending on the point of impact. However, a direct determination of this point of impact is only possible with a high level of technical effort. Also, continuous control based on the point of impact, which is only ever defined at event times, especially at the times when the hammer actually strikes the anvil, is naturally not possible.

This is where the solution presented here comes in. It was recognized that the condition of the spring element as a correlate of the impact point or at least as a measure for monitoring the can be particularly useful for improving hitting behavior.

If the temporal progression of the state of the spring element is monitored, local minima and local maxima can correspond to points in time at which the hammer reverses its direction of movement. In particular, the local minima can correspond to blows on the anvil or at least turning points of the hammer near the anvil. Local maxima can correspond to turning points of the hammer's direction of movement near the drive.

The state can also be recorded continuously, in particular in contrast to the recording of points in time, for example the point in time when the hammer hits the anvil. This means that the state can be used to predict an imminent blow.

The magnitude of the state at its local minimum or its local maximum can be indicative of whether an optimal hit is occurring or will occur. Thus, the hit behavior can be controlled with the help of such a prediction of the value at the next local minimum and/or the next local maximum.

Thus, by analyzing the state of the spring element, in particular by analyzing the temporal progression of its state, the controller can control the drive in such a way, for example by increasing or decreasing its torque, that the amount of the state remains in the local minima and/or in the local maxima in the desired ranges or is shifted into them. It can then be expected that at least a large proportion of the hammer's blows will hit the anvil optimally, in particular tangentially, and thus few losses and disturbances in the form of unwanted vibrations will occur.

Since this type of control can be used largely independently of the type of use of the impact wrench, such an impact wrench enables quick and comfortable work, especially with low vibration, in different usage situations.

It is conceivable to determine the input measurement value, i.e. the state, directly. For example, a voltage sensor, such as a strain gauge or a pressure sensor, can be arranged in and/or on the spring element.

It is also conceivable to determine the input measurement value indirectly. For example, the input measurement value can be determined as a relative value between an angular position of the hammer and an angular position of the drive. The angular positions can correspond to angles of rotation relative to a zero position and around a longitudinal axis formed by the drive and the drive shaft.

In conjunction with the guide slot, the difference between the two angular positions can result in a measurement that is related to the state of the spring element, for example a stress state of the spring element. Such a difference in the angular positions can also correlate, at least over a wide range, with a position of the hammer. In particular, it can correlate with the position of the hammer along the longitudinal axis.

For this purpose, the impact wrench can have a first sensor for detecting the angular position of the hammer. The first sensor can be an optical sensor, for example.

The impact wrench can have a second sensor for detecting the angular position of the drive. The second sensor can be arranged, at least in part, on the drive.

The second sensor can, for example, comprise a magnetic sensor. The magnetic sensor can be a Hall sensor.

From the above considerations it follows that it is advantageous if the control is set up to control a torque of the drive depending on a minimum value of the state. In particular, the temporal progression of the state can be analyzed and times of local minima and/or at least an amount of the state in the respective local minimum can be determined. This allows the impact behavior of the hammer relative to the anvil to be controlled.

Furthermore, undesirable vibrations, in this case for example caused by the hammer striking the drive, can be avoided if the control system is set up to control a torque of the drive depending on a maximum value of the stress state.

The drive can include a brushless motor.

The scope of the invention further includes a method for controlling an impact wrench, wherein the impact wrench comprises a tool holder attached to a drive shaft for holding a tool, in particular a screwing tool, wherein the drive shaft can be set in a tangentially striking movement by means of a rotary impact drive drivable via a drive, and wherein the rotary impact drive has an anvil assigned to the drive shaft, a hammer and a spring element acting on the hammer, wherein the drive is operatively connected to the hammer via a guide slot and wherein the impact wrench has a control for controlling the drive based on an input measured value, wherein a state of the spring element is determined as the input measured value and a rotational frequency of the drive is controlled depending on the determined state.

The process can prevent the hammer from hitting the wrong spot. Axial vibrations can be reduced. The torque transmitted to the tool holder can be maximized. This results in particularly fast and therefore comfortable work with an impact wrench that implements the process. The process can also prevent unwanted vibrations. Working with such an impact wrench can therefore be particularly comfortable and health-friendly.

The method can provide that a local minimum of the input measured value is determined and the drive is controlled depending on this minimum. In particular, a temporal progression of the input measured value can be monitored. One or more local minima of the input measured value can be determined from the temporal progression. Depending on the type of drive, it is conceivable to control a torque and/or a rotational frequency of the drive.

Alternatively or additionally, it is conceivable that a local maximum of the input measured value is determined and the drive is controlled depending on this local maximum.

The local minima and the local maxima can be correlates of different situations. For example, the local minima can correspond to times when the hammer is at least close to the anvil. The local maxima can correspond to times when the hammer is far from the anvil, for example close to the drive.

It is also conceivable to determine and/or predict a trajectory of the input measured value. This enables continuous, predictive control.

In particular, it is conceivable that the input measurement value is evaluated while the hammer approaches the anvil and/or while it moves away from it. In particular, the input measurement value can be evaluated at times when the hammer is not in contact with the anvil and/or the drive shaft.

It is conceivable that the input measurement value is determined directly and/or indirectly. Indirect determination can be carried out by measuring one or more measured values, particularly relating to the rotary impact drive, using sensors. The state can then be deduced from the measured values. For example, an angular position of the hammer can be measured. An angular position of the drive can also be measured. The state of the spring element can then be deduced from the difference between the two angular positions.

The controller can implement a closed-loop control. The closed-loop control can comprise a linear and/or a non-linear closed-loop control. For example, it can be based on a machine-trainable network. In particular, the controller can regulate in the manner of a model-predictive closed-loop control.

The control system may comprise and/or form one or more controllers.

A controller can regulate the drive depending on the local minima. This controller can preferably be activated by default to ensure stable impact behavior during normal operation.

A controller can regulate the drive depending on the local maxima. This can be activated, for example, when a limit value is exceeded.

It is also conceivable to have a controller that controls the drive depending on both the local minima and the local maxima.

The controller(s) can be activated and/or deactivated depending on the input measurement value, i.e. the state, and/or one of the angle positions. By selective Activating or deactivating controllers can reduce computing power requirements and/or the energy requirements of the controller.

Further features and advantages of the invention emerge from the following detailed description of embodiments of the invention, based on the figures of the drawing, which show details essential to the invention, and from the claims. The features shown there are not necessarily to scale and are shown in such a way that the special features of the invention can be made clearly visible. The various features can be implemented individually or in groups in any combination in variants of the invention.

Embodiments of the invention are shown in the schematic drawing and explained in more detail in the following description.

They show:

• Fig. 1 an impact wrench in a partially sectioned view;
• Fig. 2 a sectional view of a rotary impact drive of the impact wrench according to Fig. 1 ;
• Fig. 3 a method for controlling the impact wrench; and
• Fig. 4 to Fig. 6 Diagrams showing the temporal relationship between an input measurement value and the position of a hammer.

In the following description of the figures, the same reference numerals are used for identical or functionally corresponding elements in order to facilitate understanding of the invention.

Fig. 1 shows a hand-held power tool, in particular an impact wrench 10, in a partially sectioned side view. A housing 12 can be seen from which a tool holder 14 protrudes for holding a tool, for example a screw bit or a socket.

A handle area 16 with a control element 18 is formed on the housing 12. The control element 18 is designed to switch on and/or off.

A battery pack 20 is used to supply power to the impact wrench 10. The battery pack 20 has, for example, lithium-based and/or sodium-based batteries. The Impact wrench 10 can thus be operated wirelessly. The battery pack 20 can have a capacity of at least 20 Wh. The battery pack 20 can be designed to provide an electrical output of at least 400 W, in particular as peak output, for example for up to 60 seconds, in particular 10 seconds.

The impact wrench 10 also has a rotary impact drive 22. The rotary impact drive 22 is arranged inside the housing 12. It is shown in a partially sectioned view in area II .

Fig. 2 shows an enlarged view of area II from Fig. 1 Details of the rotary impact drive 22.

The rotary impact drive 22 is driven by a drive 24. The drive 24 includes, among other things, a motor 26 and a gear 27, for example a planetary gear. The motor 26 can be a brushless motor.

The tool holder 14 (see Fig. 1 ) is attached to a drive shaft 28 and can thus be driven by it in a rotating manner, in particular in a tangential manner.

The drive 24 and the drive shaft 28 define a longitudinal axis L of the impact wrench 10 (see Fig. 1 ).

The drive 24 drives a hammer 30 , which in turn periodically strikes an anvil 32. The anvil 32 in turn flows into the drive shaft 28, so that tangential blows of the hammer 30 ultimately drive the tool holder 14.

In particular, the hammer 30 can strike the anvil 32 along a circumferential direction U around the longitudinal axis L during optimal impact and thereby drive the tool holder 14.

In Fig. 2 the circumferential direction U corresponds to a direction perpendicular to the image plane of the Fig. 2 and is therefore in Fig. 2 shown only symbolically. It therefore runs radially around the longitudinal axis L.

The hammer 30 is arranged so that it can be moved parallel to the longitudinal axis L. It is located on a free End of a spring element 34. The spring element 34 is designed as a helical spring. The opposite free end of the spring element 34 is located in the area of the drive 24.

The hammer 30 is positively guided on a guide slot 35 and is operatively connected to the drive 24 via this. The guide slot 35 is approximately V-shaped. If the drive 24 is thus set in motion, the hammer 30 is periodically moved axially back and forth while simultaneously rotating about the longitudinal axis L, so that it ultimately strikes the anvil 32 periodically.

To control the impact movements, the impact wrench 10 has a controller 36. The controller 36 comprises a microcontroller 38 on which program code 42 stored in a memory 40 can be executed.

The program code 42, and thus the controller 36, is set up, when executed on the microcontroller 38, to determine an input measurement value ϕ as a relative value of the measured values of the first sensor 44 and the measured value of the second sensor 46 from measured values of a first sensor 44 and a second sensor 46. Depending on the input measurement value, in particular the determined relative value, the controller 36 controls the rotational frequency of the drive 24. The rotational frequency is determined according to a function defined in connection with Fig. 3 to 5 controlled by a procedure explained in more detail below.

The first sensor 44 is designed to detect an angular position of the hammer 30. The second sensor 44 is designed to detect an angular position of the drive. As described above, the input measurement value ϕ can thus correspond to an extent to which the spring element 34 is lengthened or shortened and thus tensioned accordingly. Over a wide range, the input measurement value ϕ also correlates linearly with the position of the hammer 30 along the longitudinal axis L. The angular positions of the hammer 30 and the drive are standardized in such a way that an input measurement value ϕ of 0 radians corresponds to the most relaxed state of the spring element 34, and thus also to its longest length.

The two sensors 44, 46, in particular the second sensor 46, can comprise magnetic sensors, for example Hall sensors.

Fig. 3 represents a method 1000 in which the controller 36 controls the motor 26, in particular by controlling a torque of the motor 26 , the rotational frequency f is controlled. The method 1000 is implemented by appropriate design of the program code 42 (see Fig. 2 ) and subsequent execution of the program code 42 on the controller 36.

In a variant of the method 1000, it is provided that the input measurement value ϕ, thus a measure of a state, in particular a stress state, of the spring element 34 (see Fig. 2 ), which is determined by the controller 36.

Depending on the input measurement value ϕ, the controller 36 can then set a torque and thus the rotational frequency f of the motor 26. As a result of the set torque or rotational frequency f, the movement of the hammer 30 and the spring element 34 clamped between the hammer 30 and the drive 24 can be controlled by continuously measuring the measured values of the sensors 44, 46 and subsequently processing these measured values by the controller 36 in the manner of a control loop.

In particular, the controller 36 can be configured to determine times and amounts of local minima and/or local maxima of the input measured value ϕ in order to control the motor 26.

Fig. 4 to Fig. 6 show diagrams of temporal progressions of the input measurement value ϕ, measured in radians, and a position z, measured in millimeters, of the hammer 30. The position z describes the position of the hammer 30 along the longitudinal axis L. A position z = 0 mm corresponds to a position of the hammer 30 at which the hammer 30 can execute an optimal blow against the anvil 32. The more positive the value of the position z, the closer the hammer 30 is to the free end of the spring element 34 facing the drive 24 and thus the further away from the anvil 32.

In Fig. 4 to Fig. 6 Furthermore, local maxima Ma and local minima Mi of the input measured value ϕ are marked.

In Fig. 4 a situation is shown in which the input measurement value ϕ has a positive value, here approximately 0.5 rad, at the minimum Mi. At the minimum Mi, the spring element 34 does not reach its most relaxed state. Impacts of the hammer 30 on the anvil 32 occur too early, i.e. before the actually optimal times. In such a situation, the control 36 can reduce the rotational frequency f by adjusting the torque.

In Fig. 5 a situation is shown in which the input measurement value ϕ has a value of approximately 0 rad at the minimum Mi. At the minimum Mi, the spring element 34 is therefore in its most relaxed state. Impacts of the hammer 30 on the anvil 32 thus occur at the optimal time; the control 36 can maintain the current rotation frequency f. The spring element 34 can be preloaded so that it has a certain preload even in this most relaxed state.

In Fig. 6 a situation is shown in which the input measurement value ϕ in the local minimum Mi is negative and reaches, for example, approximately -0.3 rad. In the local minimum Mi, the spring element 34 is located beyond its intended rest position. Impacts of the hammer 30 on the anvil 32 therefore occur too late; to correct this, the control 36 can increase the current rotational frequency f by adjusting the torque.

In all three situations according to the Fig. 4 to 6 It can be seen that the temporal courses of the input measured value ϕ in areas around the local maxima Ma are free of kinks, i.e. continuously differentiable.

However, it is also conceivable that the input measurement value ϕ exceeds a defined threshold value, in particular a capping of the input measurement value ϕ can occur. The temporal progression of the input measurement value ϕ in the area of the local maxima can exhibit a kink. Such situations can indicate that the hammer 30 is oversteering when sliding back in the direction of the drive 24 or even hitting a stop on the side of the drive 24.

In such a case, the controller 36 can, for example, reduce the rotational frequency f or temporarily deactivate the drive 24 in order to feed less power into the rotary impact drive 22 and thereby reduce or even avoid further undesirable vibrations.

List of reference symbols

10

Impact wrench

12

Housing

14

tool holder

16

grip area

18

control element

20

battery pack

22

rotary impact drive

24

drive

26

Motor

27

transmission

28

drive shaft

30

hammer

32

anvil

34

spring element

35

leadership backdrop

36

steering

38

microcontroller

40

memory

42

program code

44

first sensor

46

second sensor

1000

Proceedings

ϕ

input measurement value

II

Area

L

longitudinal axis

Ma

Maxima

Wed

minima

U

circumferential direction

f

rotational frequency

z

position

Claims (11)

Impact wrench (10), comprising a tool holder (14) attached to a drive shaft (28) for holding a tool, in particular a screwing tool, wherein the drive shaft (28) can be set into a tangentially striking movement by means of a rotary impact drive (22) drivable via a drive (24), and wherein the rotary impact drive (22) has an anvil (32) associated with the drive shaft (28), a hammer (30) and a spring element (34) acting on the hammer (30), wherein the drive (24) is operatively connected to the hammer (30) via a guide slot (35) and wherein the impact wrench (10) has a control (36) for controlling the drive (24) based on an input measured value (ϕ),
characterized by
that the input measured value (ϕ) corresponds to a state of the spring element (34). Impact wrench (10) according to the preceding claim, characterized in that the input measurement value (ϕ) is determined as a relative value between an angular position of the hammer (30) and an angular position of the drive (24). Impact wrench (10) according to one of the preceding claims, characterized in that the impact wrench (10) has a first sensor (44) for detecting the angular position of the hammer (30). Impact wrench (10) according to one of the preceding claims, characterized in that the impact wrench (10) has a second sensor (46) for detecting the angular position of the drive (24). Impact wrench (10) according to one of the preceding claims, characterized in that the second sensor (46) comprises a magnetic sensor. Impact wrench (10) according to one of the preceding claims, characterized in that the controller (36) is arranged to control the drive (24) as a function of a local minimum of the input measured value (ϕ). Impact wrench (10) according to one of the preceding claims, characterized in that the control (36) is arranged to control the drive (24) depending on from a local maximum of the input measurement value (ϕ). Method (1000) for controlling (36) an impact wrench (10), wherein the impact wrench (10) comprises a tool holder (14) attached to a drive shaft (28) for receiving a tool, in particular a screwing tool, wherein the drive shaft (28) can be set into a tangentially striking movement by means of a rotary impact drive (22) drivable via a drive (24), and wherein the rotary impact drive (22) has an anvil (32) associated with the drive shaft (28), a hammer (30) and a spring element (34) acting on the hammer (30), wherein the drive (24) is operatively connected to the hammer (30) via a guide slot (35) and wherein the impact wrench (10) has a controller (36) for controlling the drive based on an input measured value (ϕ),
characterized by that a state of the spring element (34) is determined as the input measured value (ϕ) and that the drive (24) is controlled depending on the state of the spring element (34). Method (1000) according to the preceding claim, characterized in that a local minimum of the input measured value (ϕ) is determined and the drive (24) is controlled as a function of this local minimum. Method (1000) according to one of the preceding claims 8 or 9, characterized in that a local maximum of the input measured value (ϕ) is determined and the drive (24) is controlled as a function of this maximum. Method (1000) according to one of the preceding claims 8 to 10, characterized in that the input measurement value (ϕ) is evaluated while the hammer (30) approaches the anvil (32) or moves away from it.

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