Impact screwdriver and method for controlling an impact screwdriver

Abstract

The invention relates to an impact screwdriver (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 tangentially impacting movement by means of a rotary impact drive (22) which can be driven by 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 slotted guide (35) and wherein the impact screwdriver (10) has a controller (36) for controlling (36) the drive based on an input measurement value (φ), characterised in that a state of the spring element (34) is determined as the input value (φ), and in that the drive (24) is controlled depending on the state of the spring element (34), as a result of which it is particularly comfortable to work with the impact screwdriver (10). The invention further relates to a method (1000) for controlling an impact screwdriver (10).

Description

[0001] Impact wrench and method for controlling an impact wrench

[0002] Description

[0003] 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 into an at least partially tangential impact movement by means of a rotary impact drive drivable via 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. Furthermore, the impact wrench has a controller for controlling the drive. By controlling the drive, the behavior of the rotary impact drive can be controlled.

[0004] To achieve the most complete transfer of momentum from the hammer to the anvil and avoid vibrations, the hammer should strike the anvil as tangentially as possible. However, depending on the user's usage of the impact wrench—for example, the tool mounted in the tool holder, the type of workpiece being machined, etc.—misfires may occur in which the hammer does not strike the anvil at least completely tangentially.

[0005] For example, it may hit the anvil axially, i.e., parallel to the drive shaft. In such a case, significant vibrations can be triggered. This can also significantly reduce the effective power of the impact wrench transferred to the tool holder.

[0006] To ensure the most versatile use of the impact wrench, especially in different usage situations, it would be desirable for the impact wrench to deliver high performance from its tool holder in as many usage situations as possible. Vibrations during operation of the impact wrench should be avoided as much as possible.

[0007] 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.

[0008] The object of the present invention is therefore to provide an impact wrench and a method for controlling an impact wrench, which enables rapid and comfortable, in particular low-vibration, work in different usage situations.

[0009] The object is achieved by an impact wrench, comprising a tool holder attached to a drive shaft for receiving a tool, in particular a screwing tool, wherein the drive shaft can be set into a tangential impact 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.

[0010] The underlying idea is that comfortable and, in particular, fast work is possible if the tool holder can be driven with the highest possible torque. To achieve this, all impacts of the hammer on the anvil should be tangential. In this case, there would be no or only minimal 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 controller depending on the point of impact. However, directly determining this point of impact is only possible with a high level of technical effort. Furthermore, 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.

[0011] This is where the solution presented here comes in. It has been recognized that the condition of the spring element can be particularly useful as a correlate of the point of impact or at least as a measure for monitoring impact behavior.

[0012] If one monitors the temporal progression of the spring element's state, local minima and local maxima can correspond to points in time at which the hammer reverses its direction of motion. In particular, local minima can correspond to impacts on the anvil or at least turning points of the hammer near the anvil. Local maxima can correspond to reversal points of the hammer's direction of motion near the drive.

[0013] The state can also be recorded continuously, especially in contrast to recording specific points in time, such as the time when the hammer hits the anvil. Thus, the state can be used to predict an imminent blow.

[0014] The magnitude of the state at its local minimum or maximum can be indicative of whether an optimal hit is occurring or will occur. Thus, the hit behavior can be controlled using such a prediction of the value at the next local minimum and / or the next local maximum.

[0015] Thus, by analyzing the state of the spring element, in particular by analyzing its state over time, the controller can control the drive in such a way, for example, by increasing or decreasing its torque, that the magnitude of the state remains in the desired ranges at the local minima and / or local maxima or is shifted into these ranges. It can then be expected that at least a large portion of the hammer's impacts will hit the anvil optimally, particularly tangentially, and thus minimize losses and disturbances in the form of unwanted vibrations.

[0016] Since this type of control can be applied largely independently of the type of use of the impact wrench, such an impact wrench enables fast and comfortable, particularly low-vibration, work in a variety of usage situations.

[0017] It is conceivable to determine the input measurement value, i.e., the state, directly. For example, a stress 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.

[0018] In conjunction with the guide slot, the difference between the two angular positions can result in a measurement related to the state of the spring element, for example, its stress state. Such a difference in angular positions can also correlate, at least over a wide range, with the position of the hammer. In particular, it can correlate with the position of the hammer along its longitudinal axis.

[0019] 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.

[0020] The impact wrench may include a second sensor for detecting the angular position of the drive. The second sensor may be located, at least in part, on the drive.

[0021] The second sensor may, for example, comprise a magnetic sensor. The magnetic sensor may be a Hall sensor.

[0022] From the above considerations, it follows that it is advantageous if the controller is configured to control a torque of the drive as a function of 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 a magnitude of the state at the respective local minimum can be determined. This allows the impact behavior of the hammer relative to the anvil to be controlled.

[0023] Furthermore, unwanted vibrations, in this case for example due to impacts of the hammer on 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.

[0024] The drive can comprise a brushless motor. The scope of the invention also 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 into a tangential percussive 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 controller 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.

[0025] This process prevents misfires of the hammer. 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 this process. The process also prevents unwanted vibrations. Working with such an impact wrench can therefore be particularly comfortable and health-friendly.

[0026] The method can provide for determining a local minimum of the input measured value and controlling the drive based 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 the torque and / or rotational frequency of the drive.

[0027] 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.

[0028] The local minima and 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, near the drive. It is also conceivable to determine and / or predict a trajectory of the input measured value. This allows for continuous, predictive control.

[0029] 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.

[0030] 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.

[0031] It is conceivable that the input measured value is determined directly and / or indirectly. Indirect determination can be achieved by measuring one or more measured values, particularly those relating to the rotary impact drive, using sensors. The measured values ​​can then be used to determine the condition. For example, the angular position of the hammer can be measured. Furthermore, the angular position of the drive can be measured. The condition of the spring element can then be determined from the difference between the two angular positions.

[0032] The controller can implement closed-loop control. The closed-loop control can comprise linear and / or nonlinear control. For example, it can be based on a machine-trainable network. In particular, the controller can operate in the manner of a model-predictive control.

[0033] The control system can comprise and / or form one or more controllers.

[0034] 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.

[0035] A controller can regulate the drive based on local maximum values. This controller can be activated, for example, when a limit value is exceeded.

[0036] It is also conceivable to have a controller that controls the drive depending on both the local minima and the local maxima.

[0037] The controller(s) can be activated and / or deactivated depending on the input measured value, i.e., the state, and / or one of the angular positions. By selectively activating or deactivating controllers, the controller's computing power and / or energy consumption can be reduced.

[0038] Further features and advantages of the invention will become apparent from the following detailed description of exemplary embodiments of the invention, based on the figures of the drawing, which illustrate details essential to the invention, and from the claims. The features shown therein are not necessarily to scale and are presented in such a way that the special features of the invention can be clearly seen. The various features can be implemented individually or in combinations in variants of the invention.

[0039] The schematic drawing shows embodiments of the invention and explains them in more detail in the following description.

[0040] They show:

[0041] Fig. 1 shows an impact wrench in a partially sectioned view;

[0042] Fig. 2 is a sectional view of a rotary impact drive of the impact wrench according to Fig. 1;

[0043] Fig. 3 shows a method for controlling the impact wrench; and

[0044] Fig. 4 to Fig. 6 Diagrams of the temporal relationship between an input measured value and a position of a hammer.

[0045] In the following description of the figures, the same reference numerals are used for identical or functionally corresponding elements to facilitate understanding of the invention.

[0046] Fig. 1 shows a handheld 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 receiving a tool, for example, a screwdriver bit or a socket.

[0047] A handle area 16 with a control element 18 is formed on the housing 12. The control element 18 is designed to switch the device on and / or off.

[0048] A battery pack 20 serves to supply power to the impact wrench 10. The battery pack 20 comprises, for example, lithium-based and / or sodium-based batteries. The impact wrench 10 can thus be operated cordlessly. The battery pack 20 can have a capacity of at least 20 Wh. The battery pack 20 can be configured to provide an electrical power of at least 400 W, in particular as a peak power, for example, for up to 60 seconds, in particular 10 seconds.

[0049] The impact wrench 10 also has a rotary impact drive 22. The rotary impact drive 22 is arranged within the housing 12. It is shown in a partially sectioned view in area II.

[0050] Fig. 2 shows an enlarged view of area II from Fig. 1 showing details of the rotary impact drive 22.

[0051] 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.

[0052] 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 tangentially striking manner.

[0053] The drive 24 and the drive shaft 28 define a longitudinal axis L of the impact wrench 10 (see Fig. 1).

[0054] 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 impacts of the hammer 30 ultimately drive the tool holder 14.

[0055] In particular, with optimal impact, the hammer 30 can strike the anvil 32 along a circumferential direction U around the longitudinal axis L and thereby drive the tool holder 14.

[0056] In Fig. 2, the circumferential direction U corresponds to a direction perpendicular to the image plane of Fig. 2 and is therefore only depicted symbolically in Fig. 2. It thus runs radially around the longitudinal axis L.

[0057] The hammer 30 is arranged so as to be movable parallel to the longitudinal axis L. It is located at 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.

[0058] The hammer 30 is positively guided on a guide slot 35 and is operatively connected to the drive 24 via this slot. The guide slot 35 is approximately V-shaped. When the drive 24 is thus activated, the hammer 30 is periodically moved axially back and forth while simultaneously rotating around the longitudinal axis L, so that it ultimately strikes the anvil 32 periodically.

[0059] To control the impact movements, the impact wrench 10 has a controller 36. The controller 36 includes a microcontroller 38 on which program code 42 stored in a memory 40 can be executed.

[0060] The program code 42, and thus the controller 36, is configured, when executed on the microcontroller 38, to determine an input measured value (p 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 measured value, in particular the determined relative value, the controller 36 controls the rotational frequency of the drive 24. The rotational frequency is controlled according to a method explained in more detail in connection with Figs. 3 to 5.

[0061] The first sensor 44 is configured to detect an angular position of the hammer 30. The second sensor 44 is configured to detect an angular position of the drive. As previously described, the input measured value cp can thus correspond to the extent to which the spring element 34 is extended or shortened and thus tensioned accordingly. Over a wide range, the input measured value cp 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 such that an input measured value cp of 0 radians corresponds to the most relaxed state of the spring element 34, thus also to its longest length.

[0062] The two sensors 44, 46, in particular the second sensor 46, may comprise magnetic sensors, for example Hall sensors.

[0063] Fig. 3 illustrates a method 1000 in which the controller 36 controls the motor 26, in particular by controlling a torque of the motor 26 and its rotational frequency f. The method 1000 is implemented by appropriately designing the program code 42 (see Fig. 2) and subsequently executing the program code 42 on the controller 36.

[0064] In a variant of the method 1000, it is provided that the input measured value cp, thus a measure of a state, in particular a stress state, of the spring element 34 (see Fig. 2), is determined by the controller 36 from the measured values ​​of the first sensor 44 and the second sensor 46.

[0065] Depending on the input measured value cp, 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.

[0066] 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 cp for controlling the motor 26.

[0067] Fig. 4 to Fig. 6 show diagrams of temporal courses of the input measured value cp, 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 is, 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.

[0068] In Fig. 4 to Fig. 6, local maxima Ma and local minima Mi of the input measured value cp are also marked.

[0069] Fig. 4 shows a situation in which the input measured value cp has a positive value, here approximately 0.5 rad, at the minimum Mi. At the minimum Mi, the spring element 34 therefore 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 controller 36 can reduce the rotational frequency f by adjusting the torque. Fig. 5 shows a situation in which the input measured value cp 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 therefore occur at the optimal time; the controller 36 can maintain the current rotational frequency f. The spring element 34 can be preloaded so that it has a certain preload even in this most relaxed state.

[0070] Fig. 6 illustrates a situation in which the input measured value cp is negative at the local minimum Mi, reaching, for example, approximately -0.3 rad. At the local minimum Mi, the spring element 34 is located beyond its intended rest position. Impacts of the hammer 30 on the anvil 32 thus occur too late; to correct this, the controller 36 can increase the current rotational frequency f by adjusting the torque.

[0071] In all three situations according to Fig. 4 to 6 it can be seen that the temporal courses of the input measured value cp in areas around the local maxima Ma are free of kinks, i.e. continuously differentiable.

[0072] However, it is also conceivable that the input measured value cp exceeds a defined threshold; in particular, a capping of the input measured value cp may occur. The temporal progression of the input measured value cp in the area of ​​the local maxima may exhibit a kink. Such situations may indicate that the hammer 30 is oversteering when sliding back toward the drive 24 or even hitting a stop on the drive 24 side.

[0073] 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 prevent further unwanted vibrations.

[0074] 10 impact wrenches

[0075] 12 housings

[0076] 14 Tool holder

[0077] 16 Grip area

[0078] 18 Control element

[0079] 20 battery pack

[0080] 22 Rotary impact drive

[0081] 24 drive

[0082] 26 Engine

[0083] 27 gearboxes

[0084] 28 Drive shaft

[0085] 30 hammers

[0086] 32 anvil

[0087] 34 spring element

[0088] 35 leadership backdrop

[0089] 36 Control

[0090] 38 microcontrollers

[0091] 40 storage

[0092] 42 Program code

[0093] 44 first sensor

[0094] 46 second sensor

[0095] 1000 Procedure cp Input measured value

[0096] II Area

[0097] L Longitudinal axis

[0098] Ma Maxima

[0099] My Minima

[0100] U Circumferential direction f Rotational frequency z Position

Claims

Patent claims 1. 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) 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 controller (36) for controlling the drive (24) based on an input measured value (cp), characterized in that the input measured value (cp) corresponds to a state of the spring element (34).

2. Impact wrench (10) according to the preceding claim, characterized in that the input measured value (cp) is determined as a relative value between an angular position of the hammer (30) and an angular position of the drive (24).

3. 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).

4. 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).

5. Impact wrench (10) according to one of the preceding claims, characterized in that the second sensor (46) comprises a magnetic sensor.

6. 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 (cp).

7. Impact wrench (10) according to one of the preceding claims, characterized in that the control (36) is arranged to control the drive (24) in dependence from a local maximum of the input measured value (cp).

8. 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 impacting 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 (cp), characterized in that a state of the spring element (34) is determined as the input measured value (cp), and that the Drive (24) is controlled depending on the state of the spring element (34).

9. Method (1000) according to the preceding claim, characterized in that a local minimum of the input measured value (cp) is determined and the drive (24) is controlled as a function of this local minimum.

10. Method (1000) according to one of the preceding claims 8 or 9, characterized in that a local maximum of the input measured value (cp) is determined and the drive (24) is controlled as a function of this maximum.

11. Method (1000) according to one of the preceding claims 8 to 10, characterized in that the input measured value (cp) is evaluated while the hammer (30) approaches the anvil (32) or moves away from it.

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