Impact wrench and method for controlling impact wrench

Abstract

An impact wrench (10) is disclosed, comprising a tool fitting (14) mounted on a drive shaft (28) for receiving a tool, in particular a screwing tool, in which the drive shaft (28) can be placed in a tangential impact movement by means of a rotary impact drive (22) which can be driven via a drive (24), and in which the drive shaft (28) can be moved in a tangential impact movement by means of a rotary impact drive (22) which can be driven via a drive (24). The rotary impact driver (22) has an anvil (32) associated with the drive shaft (28), a hammer (30) and a spring element (34) acting on the hammer (30), in which the driver (24) is operatively connected to the hammer (30) via a guide slot (35), and in which the impact wrench (10) has a control system (36) for controlling the driver based on a measured input value (phi), the impact wrench (10) is characterized in that the state of the spring element (34) is determined as a measurement input value (phi), and the drive (24) is controlled as a function of the state of the spring element (34), thereby enabling particularly comfortable work with the impact wrench (10). The invention also relates to a method (1000) for controlling an impact wrench (10).

Description

Technical Field

[0001] The present invention relates to a power tool having a rotary impact driver, and in particular to an impact wrench. The impact wrench includes a tool accessory mounted on a drive shaft for receiving a tool. For example, the tool may be a screwdriver. The drive shaft can be set into at least partially tangential impact motion by means of a rotary impact driver that can be driven by a driver. The rotary impact driver includes an anvil associated with the drive shaft, a hammer, and a spring element acting on the hammer. The driver is operatively connected to the hammer via a guide slot. The impact wrench also includes a control system for controlling the driver. The behavior of the rotary impact driver can be controlled by controlling the driver. Background Art

[0002] In order to achieve the most complete possible transfer of momentum from the hammer to the anvil and to avoid vibrations, the hammer should strike the anvil tangentially as far as possible. However, depending on the circumstances in which the user uses the impact wrench, for example, depending on which tool is contained in the tool attachment, the type of workpiece to be machined by the tool, etc., mis-strikes may occur in which the hammer does not strike the anvil tangentially, or at least not completely.

[0003] The hammer may strike the anvil axially, that is to say for example parallel to the drive shaft. In this case, significant vibrations may be generated. In addition, the power of the impact wrench that is effectively transmitted to the tool accessory may therefore be significantly reduced.

[0004] Therefore, in order to be able to use the impact wrench in the most versatile way possible, in particular in different use cases, it would be desirable for the impact wrench to provide high power at its tool attachment in as many use cases as possible. Vibrations during operation of the impact wrench should be avoided as much as possible.

[0005] However, impact wrenches generally cannot easily detect specific usage conditions, and therefore for control purposes the control system cannot rely on input parameters that directly describe the usage conditions. Summary of the Invention

[0006] It is therefore an object of the present invention to provide an impact wrench and a method for controlling an impact wrench which allow fast and comfortable, in particular low-vibration, operation in different situations of use.

[0007] This object is achieved by an impact wrench comprising a tool accessory, which is mounted on 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 driver which can be driven via a driver, and wherein the rotary impact driver has an anvil associated with the drive shaft, a hammer, and a spring element which acts on the hammer, wherein the driver is operatively connected to the hammer via a guide slot, and wherein the impact wrench has a control system for controlling the driver based on measured input values, wherein the measured input values ​​correspond to the state of the spring element.

[0008] A fundamental consideration here is that comfortable and, in particular, fast work is possible if the tool attachment can be driven with the maximum possible torque. To this end, all impacts of the hammer on the anvil should occur tangentially. In this case, there should be no or only slight vibrations in the axial direction. To this end, it is theoretically possible to repeatedly determine the point of impact of the hammer on the anvil and then control the drive based on this point using a control system. However, direct determination of this point of impact is only possible with considerable technical effort. Furthermore, due to the very nature of the situation, continuous control based on the point of impact is not possible; the point of impact is defined only at the time of the event, specifically when the hammer actually strikes the anvil.

[0009] This is where the solution proposed here comes in. This is because it has been recognized that the state of the spring element can be particularly useful as a link to the impact point or at least as a measure for monitoring the impact behavior.

[0010] Thus, if the state of the spring element is monitored over time, local minima and local maxima can each correspond to a time when the hammer reverses its direction of motion. In particular, a local minimum can correspond to an impact with the anvil, or at least a point where the hammer returns near the anvil. A local maximum can each correspond to a point where the hammer's direction of motion reverses near the driver.

[0011] The state can also be detected continuously, in particular in contrast to the detection of, for example, time (eg the time when the hammer strikes the anvil). Thus, by means of the state, an impending impact can be predicted.

[0012] The absolute value of the state at its local minimum or its local maximum can indicate whether an optimal shock has occurred or will occur. Thus, the shock behavior can be controlled with the help of this prediction of the value at the next local minimum and / or the next local maximum.

[0013] Thus, by analyzing the state of the spring element, in particular by analyzing the change in the state of the spring element over time, the control system can control the drive, for example, increase or reduce its torque, in such a way that the absolute value of the state at the local minimum and / or local maximum remains within or moves into the corresponding desired range. It can then be expected that at least the majority of the hammer's impacts will strike the anvil in an optimal manner, in particular tangentially, and that therefore losses and disturbances in the form of undesirable vibrations will occur less frequently.

[0014] Since this type of control can be used largely independently of the respective manner in which the impact wrench is used, it is possible to work quickly and comfortably, in particular with low vibrations, with such an impact wrench in various situations of use.

[0015] It is conceivable to directly determine the measured input value, ie the state. For example, a stress sensor (eg a strain gauge or a pressure sensor) can be arranged in and / or on the spring element.

[0016] The measured input value can also be determined indirectly. For example, the measured input value can be determined as a relative value between the angular position of the hammer and the angular position of the driver. The angular position can correspond to a rotation angle relative to a zero position and about a longitudinal axis formed by the driver and the drive shaft.

[0017] In combination with the guide slot, a metric related to the state of the spring element (e.g., the stress state of the spring element) can be derived from the difference between the two angular positions. This difference between the angular positions can also be correlated, at least over a broad range, to the position of the hammer. In particular, it can be correlated to the position of the hammer along the longitudinal axis.

[0018] For this purpose, the impact wrench may have a first sensor for detecting the angular position of the hammer. For example, the first sensor may be an optical sensor.

[0019] The impact wrench may have a second sensor for detecting the angular position of the driver. The second sensor may be arranged at least partially on the driver.

[0020] For example, the second sensor may include a magnetic sensor. The magnetic sensor may be a Hall effect sensor.

[0021] In light of the above considerations, it appears advantageous to design the control system so as to control the torque of the drive as a function of the local minimum of the state. In particular, the evolution of the state over time can be analyzed, and the time of the local minimum and / or at least one absolute value 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.

[0022] Furthermore, undesirable vibrations, which in this case are caused, for example, by impacts of a hammer on the drive, can be avoided if the control system is designed to control the torque of the drive as a function of the maximum value of the stress state.

[0023] In this case, the drive may comprise a brushless motor.

[0024] The scope of the present invention also includes a method for controlling an impact wrench, wherein the impact wrench comprises a tool accessory, which is mounted on 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 driver that can be driven via a driver, and wherein the rotary impact driver has an anvil associated with the drive shaft, a hammer, and a spring element that acts on the hammer, wherein the driver is operatively connected to the hammer via a guide slot, and wherein the impact wrench has a control system for controlling the driver based on measured input values, wherein the state of the spring element is determined as the measured input value, and the rotational frequency of the driver is controlled as a function of the detected state.

[0025] This method prevents accidental hammer strikes. Axial vibrations can be reduced. The torque transmitted to the tool accessory can be maximized. This allows for particularly fast and therefore comfortable working with an impact wrench implementing this method. Unwanted vibrations can also be avoided with this method. Consequently, working with this impact wrench can be performed in a particularly comfortable and healthy manner.

[0026] The method can be used to determine a local minimum of a measured input value and to control a drive based on this minimum. In particular, the change in the measured input value over time can be monitored. Based on this change over time, one or more local minima of the measured input value can be determined. 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 to determine a local maximum of the measured input value and to control the drive as a function of this local maximum.

[0028] Local minima and local maxima can be associated with different situations. For example, a local minimum can correspond to the time when the hammer is at least near the anvil. A local maximum can correspond to the time when the hammer is away from the anvil, such as near the driver.

[0029] It is also conceivable to determine and / or predict the trajectory of the measured input values, so that a continuous predictive control can be performed.

[0030] In particular, for this purpose, it is conceivable to evaluate the measured input value when the hammer is approaching the anvil and / or moving away from the anvil. In particular, the measured input value can be evaluated at a time during which the hammer is not in contact with the anvil and / or the drive shaft.

[0031] It is conceivable to determine the measured input values ​​directly and / or indirectly. Indirect determination can be performed by measuring one or more measured values ​​using a sensor, particularly those related to the rotary impact driver. The state can then be inferred from the measured values. For example, the angular position of the hammer can be measured. Alternatively, the angular position of the driver can be measured. Based on the difference between these two angular positions, the state of the spring element can then be inferred.

[0032] The control system can implement closed-loop control. The closed-loop control can include linear and / or nonlinear closed-loop control. For example, the closed-loop control can be based on a network capable of machine training. In particular, the control system can implement control in the manner of a closed-loop model predictive control system.

[0033] The control system may include and / or form one or more controllers.

[0034] The controller may control the drive according to the local minimum.This controller may preferably be enabled in a standard manner in order to ensure a stable impulse behavior during normal operation.

[0035] The controller can control the drive according to local maxima. For example, this controller can be activated when a limit value is exceeded.

[0036] It is also conceivable to control the controller of the drive as a function of the local minima and local maxima.

[0037] The controller or controllers may be enabled and / or disabled based on a measured input value (ie, state) and / or one of the angular positions. By selectively enabling or disabling controllers, the computational power requirements and / or energy requirements of the control system may be reduced.

[0038] Further features and advantages of the present invention will become apparent from the following detailed description of exemplary embodiments of the invention, with reference to the accompanying drawings, which illustrate details essential to the invention, and from the claims. The features shown therein are not necessarily to scale, but are presented in such a way that the special features according to the invention can be clearly visualized. In variants of the invention, the various features may be implemented individually or collectively in any combination. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Exemplary embodiments of the invention are shown in the schematic drawings and explained in detail in the following description.

[0040] In the attached figure:

[0041] Figure 1 shows a partial cross-sectional view of an impact wrench;

[0042] Figure 2 Shown Figure 1 A cross-sectional view of a rotary impact driver of an impact wrench;

[0043] Figure 3 A method for controlling an impact wrench is shown; and

[0044] Figures 4 to 6 A graph showing the relationship between the measured input value and the position of the hammer with respect to time is shown.

[0045] In the following description of the figures, the understanding of the invention is facilitated by the use in each case of the same reference numerals for identical or functionally corresponding elements. DETAILED DESCRIPTION

[0046] Figure 1 There is shown a partially cut-away side view of a handheld power tool, in particular an impact wrench 10. The figure shows a housing 12 from which a tool accessory 14 projects for receiving a tool, such as a screwdriver bit or socket.

[0047] A handle region 16 with an operating element 18 is formed on the housing 12. The operating element 18 is designed for opening and / or closing.

[0048] The rechargeable battery pack 20 is used to supply energy to the impact wrench 10. For example, the rechargeable battery pack 20 includes lithium-based and / or sodium-based rechargeable batteries. This allows the impact wrench 10 to be operated wirelessly. The rechargeable battery pack 20 may have a capacity of at least 20 Wh. The rechargeable battery pack 20 may be configured to provide at least 400 W of electrical power, particularly as peak power, for example, for up to 60 seconds, particularly 10 seconds.

[0049] The impact wrench 10 further comprises a rotary impact driver 22. The rotary impact driver 22 is arranged in the housing 12. The rotary impact driver 22 is shown in a partial cross-sectional view in the area II.

[0050] Figure 2 by Figure 1 The enlarged view of region II shows details of the rotary impact driver 22 .

[0051] The rotary impact driver 22 is driven by a driver 24. The driver 24 comprises, in particular, a motor 26 and a transmission 27 (eg, a planetary transmission). The motor 26 may be a brushless motor.

[0052] Tool accessories 14 (see Figure 1) is mounted on the drive shaft 28 and can thus be driven in rotation by the drive shaft (in particular by a tangential impact action).

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

[0054] The driver 24 drives a hammer 30 which in turn periodically strikes an anvil 32. The anvil 32 in turn merges into the drive shaft 28, with the result that the hammer 30 ultimately tangentially impacts the tool assembly 14.

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

[0056] exist Figure 2 In the circumferential direction U, the circumferential direction corresponds to the direction perpendicular to Figure 2 direction of the image plane and thus in Figure 2 The circumferential direction therefore extends radially around the longitudinal axis L.

[0057] The hammer 30 is arranged in such a way that it can move parallel to the longitudinal axis L. The hammer is located at the 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 region of the driver 24.

[0058] The hammer 30 is guided along the guide slot 35 under constraint and is operatively connected to the driver 24 via the guide slot. The guide slot 35 is generally V-shaped. Therefore, if the driver 24 is put into operation, the hammer 30 periodically moves axially backward and forward while rotating about the longitudinal axis L, with the result that the hammer 30 eventually strikes the anvil 32 periodically.

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

[0060] When executed on the microcontroller 38, the program code 42, and therefore the control system 36, is designed to use the measured values ​​from the first sensor 44 and the second sensor 46 to convert the measured input values ​​into is determined as a relative value of the measured value from the first sensor 44 and the measured value from the second sensor 46. The control system 36 controls the rotational frequency of the drive 24 according to the measured input value (that is, in particular the determined relative value). Figures 3 to 5 The method to control the rotation frequency is explained in more detail.

[0061] In this case, the first sensor 44 is designed to detect the angular position of the hammer 30. The second sensor 46 is designed to detect the angular position of the driver. As described above, the measurement input value It is thus possible to correspond to the extent to which the spring element 34 is stretched or shortened and thus subjected to a corresponding stress. It is also linearly dependent on the position of the hammer 30 along the longitudinal axis L. Here, the angular position of the hammer 30 and the angular position of the driver are normalized in such a way that the measured input value of 0 radians is corresponds to the most relaxed state of the spring element 34 and therefore also to its maximum length.

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

[0063] Figure 3 A method 1000 is shown in which the control system 36 controls the motor 26, in particular by controlling the torque of the motor 26 at the rotational frequency f. The method 1000 is implemented by correspondingly configuring the program code 42 (see Figure 2 ) and subsequently executing the program code 42 on the control system 36.

[0064] In a variant of the method 1000 , it is envisaged that the control system 36 determines the measurement input value based on the measurement values ​​of the first sensor 44 and the second sensor 46 . , that is, a measure of the state, in particular the state of tension, of the spring element 34 is thus determined (see Figure 2 ).

[0065] The control system 36 can then use the measured input values ​​to The torque and thus the rotational frequency f of the motor 26 are set. By means of the set torque or rotational frequency f, the movement of the hammer 30 and the movement of the spring element 34 clamped between the hammer 30 and the driver 24 can be controlled by the control system 36 in a closed control loop by continuously measuring the measured values ​​of the sensors 44, 46 and subsequently processing these measured values.

[0066] In particular, the control system 36 may be designed to determine the measured input values The time and absolute value of the local minimum and / or local maximum of the motor 26 are used to control the motor 26.

[0067] Figures 4 to 6 The measured input value of hammer 30 is shown Graph of the time course of position z (measured in radians) and position z (measured in millimeters). Position z describes the position of hammer 30 along longitudinal axis L. Position z=0 mm corresponds to a position of hammer 30 in which hammer 30 can optimally impact anvil 32. The more positive the value of position z, the closer hammer 30 is to the free end of spring element 34 (the end facing driver 24) and therefore the further away from anvil 32.

[0068] exist Figures 4 to 6 The measured input value is also indicated in The local maximum Ma and local minimum Mi of .

[0069] Figure 4 Shows the measured input values The minimum value Mi has a positive absolute value (in this case, approximately 0.5 rad). Therefore, at the minimum value Mi, the spring element 34 has not reached its most relaxed state. The impact of the hammer 30 on the anvil 32 occurs too early, that is, before the actual optimal time. In this case, the control system 36 can reduce the rotation frequency f by adjusting the torque.

[0070] Figure 5 Shows the measured input values At the minimum value Mi, the spring element 34 has an absolute value of approximately 0 rad. Therefore, at the minimum value Mi, the spring element 34 is in its most relaxed state. Therefore, the impact of the hammer 30 on the anvil 32 occurs at the optimal time; the control system 36 can maintain the current rotation frequency f. In this case, the spring element 34 can be prestressed to ensure that it has a certain prestress even in this most relaxed state.

[0071] Figure 6 Shows the measured input values In the case of a local minimum Mi, the rotational frequency f is negative and reaches, for example, approximately -0.3 rad. At the local minimum Mi, the spring element 34 exceeds its conceivable rest position. Consequently, the hammer 30 strikes the anvil 32 too late. To correct this, the control system 36 can increase the current rotational frequency f by adjusting the torque.

[0072] exist Figures 4 to 6 In all three cases shown, it can be seen that the measured input values The change with respect to time has no sharp bend within the range around the local maximum Ma, that is, it is continuously differentiable.

[0073] However, it is also conceivable that the measured input value will exceed the defined threshold, in particular the measured input value may occur Measured input value The time profile in the region of the local maximum may have a sharp curve. This may indicate that the hammer 30 overshoots or even hits a stop at the driver 24 when sliding back in the direction of the driver 24 .

[0074] In this case, the control system 36 can reduce the rotational frequency f or briefly deactivate the drive 24 , for example, in order to feed less power into the rotary impact drive 22 and thus reduce or even avoid further undesirable vibrations.

[0075] List of Reference Numerals

[0076] 10 Impact wrench

[0077] 12 Housing

[0078] 14 Tool Accessories

[0079] 16 Handle area

[0080] 18 operating elements

[0081] 20 rechargeable battery packs

[0082] 22 Rotary Impact Drivers

[0083] 24 Drive

[0084] 26 Motor

[0085] 27 Transmission

[0086] 28 drive shaft

[0087] 30 Hammer

[0088] 32 Anvil

[0089] 34 Spring element

[0090] 35 guide slot

[0091] 36 Control System

[0092] 38 microcontroller

[0093] 40 Memory

[0094] 42 Program Code

[0095] 44 First Sensor

[0096] 46 Second sensor

[0097] 1000 methods

[0098] Measured input value

[0099] II Area

[0100] L longitudinal axis

[0101] Ma maximum value

[0102] Mi minimum value

[0103] U Circumferential direction

[0104] f rotation frequency

[0105] Z position

Claims

1. An impact wrench (10), comprising a tool accessory (14), which is mounted on a drive shaft (28) and is used to receive a tool, in particular a screwing tool, wherein: The drive shaft (28) can be set in a tangential impact motion by means of a rotary impact driver (22) which can be driven via a driver (24), and wherein the rotary impact driver (22) has an anvil (32) associated with the drive shaft (28), a hammer (30) and a spring element (34) which acts on the hammer (30), wherein the driver (24) is operatively connected to the hammer (30) via a guide slot (35), and wherein the impact wrench (10) has a control system (36) for controlling the driver (24) based on a measured input value (φ), It is characterized by: The measured input value (φ) corresponds to the state of the spring element (34).

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

3. The 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 driver (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 control system (36) is designed to control the actuator (24) according to the local minimum of the measured input value (φ).

7. Impact wrench (10) according to one of the preceding claims, characterized in that The control system (36) is designed to control the drive (24) according to the local maximum of the measured input value (φ).

8. A method (1000) for controlling (36) an impact wrench (10), wherein: The impact wrench (10) comprises a tool accessory (14) mounted on a drive shaft (28) for receiving a tool, in particular a screwing tool, wherein the drive shaft (28) can be set into a tangential impact movement by means of a rotary impact driver (22) drivable via a driver (24), and wherein the rotary impact driver (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 driver (24) is operatively connected to the hammer (30) via a guide slot (35), and wherein the impact wrench (10) has a control system (36) for controlling the driver based on a measured input value (φ). It is characterized by: The state of the spring element (34) is determined as a measured input value (φ), and the drive (24) is controlled depending on the state of the spring element (34).

9. The method (1000) according to the preceding claim, characterized in that A local minimum of the measured input value (φ) is determined, and the driver (24) is controlled according to the local minimum.

10. The method (1000) according to any one of claims 8 or 9, characterized in that A local maximum of the measured input value (φ) is determined, and the driver (24) is controlled according to the maximum.

11. The method (1000) according to one of claims 8 to 10, characterized in that The measured input value (φ) is evaluated as the hammer (30) moves toward or away from the anvil (32).

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