Electronically triggered torque wrench

Abstract

Electronic torque wrench (10) for tightening screw connections with a predetermined nominal torque, comprising a) a lever housing (12), b) a grip area (14) of the lever housing (12) for force application, c) a head area (16) with a drive part (46) for transmitting a torque to a workpiece, d) a main actuating arm (20) which is provided on the drive side in the lever housing (12), e) a measuring sensor (22) on the main actuating arm (20) and / or a bending element for detecting the applied torque, wherein the measuring sensor (22) outputs a signal corresponding to this torque to a signal processing and control unit (24), f) an adjustment mechanism (26) and / or adjustment electronics for setting the desired target torque, g) a release mechanism (28) for releasing the torque at the target torque, wherein the release mechanism (28) is controlled by the signal processing and control unit (24), characterized in that h) the release mechanism (28) comprises a cam wheel (38) over whose cam (64) the main actuating arm (20) moves to release.

Description

Technical field

[0001] The innovation concerns an electronic torque wrench for tightening screw connections with a predefined target torque. a) a lever housing, b) a grip area of ​​the lever housing for force application, c) a head area with a drive component for transmitting torque to a workpiece, d) a main actuating arm, which is provided on the drive side in the lever housing, e) a measuring sensor on the main actuating arm and / or a bending element for detecting the applied torque, wherein the measuring sensor outputs a signal corresponding to this torque to a signal processing and control unit, f) an adjustment mechanism and / or adjustment electronics for setting the desired target torque, g) a release mechanism for releasing the torque at the target torque, wherein the release mechanism is controlled by the signal processing and control unit. Description

[0002] Screw connections are the most frequently used type of joint in mechanical engineering. Such fasteners can only be effective when using appropriate assembly tools. These include torque tools such as torque screwdrivers and torque wrenches. Torque tools are required to apply a specific torque to a workpiece.

[0003] Torque tools include, for example, torque wrenches and torque screwdrivers. There are mechanical and electronic torque tools. Specifically, there are indicator and click-type torque tools. Indicator torque tools always display the currently applied torque. With click-type torque tools, a target torque is set. As soon as this torque is reached when tightening a fastener, the torque tool signals to the user. This can be indicated, for example, by an audible click or a tactile crack. The release mechanism can be designed in various ways. For example, even when the target torque is reached, it can be prevented from applying a higher torque to a workpiece than the set target torque.

[0004] The torque to be applied when using hand-held tools depends on both the user's physical constitution and their subjective perception of force. Torque tools are used to apply a high preload force to a screw, within the screw's elastic range, or to apply only low preload forces. The use of new construction materials such as magnesium, aluminum, or plastics, especially for lightweight construction in the automotive and aerospace industries, is increasing both the demand for and the requirements placed on torque tools. These new materials increase the number of sensitive bolted connections. The lower tensile strength of these lightweight materials compared to steel would lead to thread damage if the bolted connection was overstressed, rendering these expensive components unusable. State of the art

[0005] Various electronic torque wrenches are known from the prior art, which have both mechanical and electronic components for detecting and limiting the torque.

[0006] German patent DE 20315000 U1 discloses an electronic torque wrench with a rod-shaped housing that has a handle at one end and a tool holder at the other. Inside the housing are a device for measuring torque and a device for measuring the angle of rotation. Torque is measured using strain gauges designed as solid bridges and mounted on a bending rod. An electronic evaluation unit with a microprocessor is also provided, which processes the measured values ​​and displays them on a screen. A data interface, such as Bluetooth, IrDA, or USB, is used to transmit the acquired data.

[0007] From EP 3372344 A1, a torque wrench is known which has a tubular cam section rotatably mounted around a drive spindle. Several cam surfaces with different torque profiles are provided on its circumference. A spring-loaded roller element rests against the cam surface and transmits the motion to the drive spindle. The cam surfaces include areas for a static holding function, for the gradual increase of the torque up to a peak value, and for the reduction of the torque after the set value has been exceeded.

[0008] EP 3737533 B1 describes an electronically actuated torque tool in which an electromagnet serves as the release element. The electromagnet acts via a movable coupling element on a mechanical lock that connects the torque-transmitting part of the tool to a housing section. When the set target value is reached, the control electronics release the magnet, which moves the coupling element into a release position and allows the torque-transmitting part to rotate relative to the housing. The document further describes a return of the release mechanism to its initial position and an electronic acquisition of the torque data.

[0009] German patent application DE 20 2011 050 280 U1 describes an adjustable torque wrench with a tool drive unit. The torque wrench has a tubular tool shaft extending longitudinally. A handle is attached to one end of the shaft and is rotatably mounted around its longitudinal axis. The handle is directly or indirectly coupled to a clamping unit inside the handle and / or tool shaft. Rotating the handle tensions or releases a coil spring, which presets the required tightening torque. The handle also features a folding lever that rests against the handle in its rest position. A scale is located in a transition area between the tool shaft and the handle, which can display numerical values ​​indicating the currently set tightening torque.The transition area is tapered compared to the tool shank, with a reduced cross-section. A second end section of the tool shank, opposite the first, serves to connect it to a tool drive component, which accommodates tools, typically attachment tools. For this purpose, the otherwise circular tool shank is flattened at its second end section, forming a rectangular opening at the end.

[0010] German patent application DE 100 51 011 A1 discloses a trigger-activated torque wrench that electronically detects the torque. A strain gauge converts the mechanical torque into an electronic signal. The detected torque is then compared to a target value. If the measured torque reaches the set or specified target torque value, the electronic evaluation triggers the mechanical release of the torque wrench, at least briefly. This release is achieved, for example, by decoupling the wrench handle from the wrench head.

[0011] In known electronic torque wrenches, the torque is often triggered by electromagnetically or mechanically actuated locking systems where the movement of the main lever is not precisely controlled. This can result in uneven triggering or dependence on friction and tolerances of the moving parts. Furthermore, in these known designs, the locking systems must be returned to their initial position or manually locked after each triggering before the torque wrench can be used again. Automatic return to the initial position of the main lever is not provided. Revelation of the innovation

[0012] The aim of this innovation is therefore to avoid the disadvantages of the prior art and to provide an electronic torque wrench that is extremely easy to use. The triggering mechanism should occur within a defined sequence of movements, and the main lever should automatically return to its starting position after triggering, without the need for manual or separate relocking.

[0013] According to the innovation, the task is solved by using an electronic torque wrench of the type mentioned above. h) the release mechanism comprises a cam wheel, over whose cam the main actuating arm moves to release.

[0014] The cam wheel geometrically determines the movement of the main actuating arm when the target torque is reached. Upon release, the main actuating arm moves across the cam surface and, due to its bearing and a restoring force, automatically returns to its starting position. The cam wheel thus causes a defined slip of the main lever, ensuring a reproducible starting position after each release without the need for a separate locking process. This significantly simplifies operation.

[0015] Surprisingly, it has been shown that the design of the release mechanism with a cam wheel achieves a smooth, mechanically guided release movement, in which the main actuating arm automatically returns to its starting position after each pass over the cam surface, thus making the torque wrench immediately ready for use again. The release mechanism is controlled by the signal processing and control unit.

[0016] The innovation is based on the principle that the cam surface of the cam wheel defines a fixed path of movement for the main actuating arm, along which it moves in a controlled manner over the cam during triggering and automatically slides back into its starting position after passing the cam tip. Thus, the triggering and return process is determined solely by the geometry of the cam wheel.

[0017] An advantageous design of the inventive electronic torque wrench results from the cam wheel being arranged in the drive unit. This allows the torque transmission to occur directly near the point of force application, thereby reducing the play between the main actuating arm and the drive and enabling more precise release.

[0018] A preferred embodiment of the inventive electronic torque wrench is achieved by incorporating a solenoid into the release mechanism, which acts directly or indirectly, via at least one further force transmission component, on the main actuating arm. This allows for electronic control of the release mechanism with minimal mechanical effort and enables precise timing control of the release.

[0019] A further advantageous embodiment of the inventive electronic torque wrench provides that the release mechanism has an elastic return mechanism, which returns the locking mechanism to its locked initial position after release. The elastic return mechanism can, for example, be designed as a spring that pushes the main actuating arm or a component coupled to it back into its initial position. This automatically returns the mechanism to its initial state, making the wrench immediately ready for use again after release and eliminating the need for manual reset.

[0020] A further advantageous design of the new electronic torque wrench consists in the main actuating arm having a cam roller at one end, which is in contact with the cam wheel. The cam roller reduces friction between the lever and the cam wheel and ensures smooth, low-wear movement across the cam surface. The cam roller can be mounted in a bearing, such as a ball or roller bearing, to further reduce friction.

[0021] A further advantageous design of the inventive electronic torque wrench is that the measuring sensor is designed as a strain gauge. This allows the applied torque to be measured with high accuracy and in a compact design, with the measured value being transmitted directly to the signal processing and control unit.

[0022] A further preferred embodiment of the inventive electronic torque wrench is achieved by the release mechanism comprising a chain lock with two levers mounted at the end of the main lever and two chain links which, in the locked state, are arranged in a substantially triangular shape. The solenoid acts on the chain links to release the lock, causing the triangular arrangement to buckle in the area of ​​the chain links and releasing the main actuating arm. This arrangement allows for a compact, mechanically stable lock that can be reliably released by the solenoid without requiring high spring forces.

[0023] An advantageous further development of the inventive electronic torque wrench provides that the release mechanism includes a locking cam which, in the locked state, blocks the movement of the main lever and is held in position by a chain lock. A solenoid acts on the chain lock, causing it to fold and release the locking cam, thereby moving the main actuating arm over the cam wheel upon release. This achieves a clearly defined, guided release movement in which the locking position of the lever is precisely determined by the cam contour.

[0024] A preferred embodiment of the inventive electronic torque wrench is achieved by incorporating a ball locking mechanism in the release mechanism. Several balls are arranged in a ring around a release pin, holding it in position when locked. When actuated, the solenoid moves the release pin, causing the balls to shift from their locked position into a radially inwardly directed recess in the release pin and releasing the locking mechanism. This releases the main actuating arm, which then moves via the cam wheel. The use of the ball locking mechanism allows for a particularly compact and low-friction release unit, ensuring a defined and repeatable unlocking process.

[0025] Further embodiments and advantages will become apparent from the subject matter of the dependent claims and the drawings with their accompanying descriptions. One exemplary embodiment is explained in more detail below with reference to the accompanying drawing. The innovation is not intended to be limited solely to this exemplary embodiment. Rather, embodiments are also envisaged which are now and in the future equivalent and obvious to a person skilled in the art using other technical aids. The aforementioned prior art shall be deemed a disclosure to this application. Brief description of the drawing Fig. Figure 1 shows a first embodiment of an electronic torque wrench with mechanical long-stroke release in a locking home position with chain links. Fig. 2 shows the torque wrench according to Fig. 1 in a position in which the chain links 36 are moved slightly beyond their dead center, with the freewheel angle of the cam wheel 38 also shown. Fig. 3 shows the torque wrench according to Fig. 1 and Fig. 2 with external structure and drive unit. Fig. 4 shows the torque wrench according to the Fig. 1 to 3 after triggering, showing the pivot angle of the main actuating arm around the bearing bolt. Fig. Figure 5 shows a second embodiment with a linearly displaceable main actuating arm and locking cam. Fig. Figure 6 shows the torque wrench after being triggered according to Fig. 5 with released locking cam and reset mechanism. Fig. 7 shows the torque wrench according to the Fig. 5 and Fig. 6 with lever housing and drive unit. Fig. Figure 8 shows the electronic torque wrench in a third embodiment in the basic position with the ball locking mechanism engaged. Fig. 9 shows the torque wrench according to Fig. 8 in the unlocked state after triggering. Fig. 10 shows the torque wrench according to Fig. 8 and Fig. 9 with lever housing and drive unit. Preferred embodiment

[0026] Fig. Figures 1 to 4 show a first embodiment of an electronic torque wrench 10 with mechanical long-stroke release. Fig. Figure 1 shows the electronic torque wrench 10 in a locked basic position. The torque wrench 10 comprises a lever housing 12 with a handle area 14 for force application and a head area 16.

[0027] Inside the lever housing 12, a main actuating arm 20 is pivotally mounted about a bearing pin 33 and is provided on the drive side of the lever housing 12. The main actuating arm 20 carries a measuring sensor 22, which is designed as a strain gauge and detects the applied torque. The output signal of the measuring sensor 22 is transmitted to a signal processing and control unit 24 located in the grip area 14. Operating elements 15 for setting the target torque and for operating the tool are located in the grip area 14. In addition, as in the other embodiments, an LED indicator and a display with common display types can be provided there, which visually signal the achievement of the target torque or various operating states; these elements are not shown in the drawing.

[0028] To set the desired target torque, an adjustment mechanism 26 is provided, which is designed as an electronic adjustment unit and is connected to the signal processing and control unit 24. The control unit 24 compares the actual torque detected by the measuring sensor 22 with the target value specified via the adjustment mechanism 26 and, when the target value is reached, activates the release mechanism 28.

[0029] The release mechanism 28 comprises an electrically actuated solenoid 30 and a chain lock 32. The chain lock 32 consists of two levers 34 mounted at the end of the main actuating arm 20 with bearing pins 33 and two chain links 36, which together form an essentially triangular joint arrangement when locked. This arrangement blocks the main actuating arm 20 relative to the lever housing 12. When the solenoid 30 is actuated, it acts on the chain links 36, causing the triangular joint structure to fold and release the lock.

[0030] In the head region 16, a cam wheel 38 is arranged, which has a cam surface 40 with an ascending and a descending area on its circumference. In the present embodiment, nine cams 64 are provided on the cam wheel. At the end of the main actuating arm 20, a cam roller 42 is located, which bears against the cam surface 40. A return mechanism 62 is provided, which automatically returns the main actuating arm 20 to its initial position after release. In a preferred embodiment, the return mechanism 62 comprises at least one return spring 44, which biases the main actuating arm 20 in the direction of the locked initial position.

[0031] In Fig. 2 is the torque wrench 10 according to Fig. Figure 1 shows the chain mechanism in a position above dead center. When the solenoid 30 is actuated, the chain locking mechanism 32 engages, and the main actuating arm 20 moves over the rising cam surface 40. In the locked starting position, the chain links 36, together with the levers 34, form an almost straight connection that defines the dead center of the chain mechanism. When the solenoid 30 is actuated, this dead center is slightly exceeded, with the articulation point of the chain links 36 being approximately 3° above the dead center. This makes the locking mechanism unstable and releases the main actuating arm 20. The cam roller 42 rolls over the apex of the cam 64 of the cam wheel 38, with this point marking the moment of release.

[0032] The cam wheel 38 has a freewheel angle of approximately 40°, which corresponds to the division of the cam wheel 38 into nine cams 64 evenly distributed around its circumference. This angle describes the section in which the cam roller 42 can freely return to its starting position after passing over a cam 64, before it again engages the next cam 64. After passing over the cam 64, the return mechanism 62 causes the main actuating arm 20 to automatically return to its initial position.

[0033] In Fig. 3 is the torque wrench 10 according to the Fig. 1 and Fig. Figure 2 shows the external structure. The lever housing 12 has the grip area 14 and the head area 16 with a drive element 46. The drive element 46 has an external square 48 onto which standardized socket wrenches or sockets can be attached. The contact between the cam roller 42 and the cam surface 40 of the cam wheel 38 is mechanically guided over the entire release stroke. The adjustment mechanism 26 is located in the grip area 14 and forms a functional unit with the signal processing and control unit 24.

[0034] In Fig. Figure 4 shows the state after triggering. The chain lock 32 is unlocked, the chain links 36 are folded, and the main actuating arm 20 has passed over the cam surface 40. The return mechanism 62 now acts on the main actuating arm 20 via the at least one return spring 44, so that it is returned to its initial position, while the chain lock 32 returns to its locked position. The pivot angle of the release mechanism 28 is approximately 15°, which describes the rotation range of the main actuating arm 20 around the bearing journal 33 from the beginning of the release until the cam surface 40 has been completely passed over.

[0035] Fig. Figures 5 to 7 show a second embodiment of an electronic torque wrench 10 with a mechanical long-stroke release. Where the components correspond to those of the previous figures, the same reference numerals are used.

[0036] In Fig. Figure 5 shows the electronic torque wrench 10, in which the release mechanism 28 includes a locking cam 50.

[0037] In this embodiment, the measuring sensor 22 is attached to the lever housing 12, which forms a bending element. When force is applied, the lever housing 12 undergoes elastic deformation, the strain of which is detected by the measuring sensor 22. The signal generated corresponds to the applied torque and is transmitted to the signal processing and control unit 24.

[0038] The main actuating arm 20 is not pivotally mounted about the bearing journal 33, but is slidably arranged in a longitudinal axis of the lever housing 12. The main actuating arm 20 is mounted in an axial guide 55, which guides its linear displacement movement within the lever housing 12. The main actuating arm 20 is coupled to the cam surface 40 of the cam wheel 38 via the cam roller 42. In its home position, the locking cam 50 blocks the movement of the main actuating arm 20 and is held in its position by the chain lock 32. The chain lock 32 has a roller 57 between the chain links 36, which allows it to move within the chain locking cam 50. The locking cam 50 is located at the end of the main actuating arm 20 opposite the cam wheel 38 and is therefore situated in an area of ​​the lever housing 12 facing away from the drive part 46.A cam spring 51 acts on the locking cam 50 and holds it in the locked initial position. Additionally, a return mechanism 62 is provided, which includes a return spring 44 that acts on the main actuating arm 20 and biases it towards its initial position.

[0039] In Fig. Figure 6 shows the device after release. The solenoid 30 acts via the guide cam 50 on a release shaft 52, causing the chain lock 32 to have a corresponding cam space 53 in the guide cam 50 and to fold into it. The release mechanism 28 is released. The main actuating arm 20 is then moved along its longitudinal axis towards the grip area 14 and moves the cam roller 42 over the cam surface 40. After passing over, the return mechanism 62 causes the main actuating arm 20 to automatically return to its locked starting position, while simultaneously the cam spring 51 brings the locking cam 50 into its locked position.

[0040] In Fig. 7 is the torque wrench 10 according to the Fig. 5 and Fig. Figure 6 shows the lever housing 12, which has the handle area 14 for applying force to the torque wrench 10 and the head area 16 with the drive part 46. The solenoid 30, the locking cam 50, the cam spring 51, the chain lock 32, the release shaft 52, and the main actuating arm 20, which is displaceable along the longitudinal axis, are arranged within the lever housing 12.

[0041] Fig. Figures 8 to 10 show a third embodiment of an electronic torque wrench 10 with a mechanical long-stroke release. Where the components shown correspond to those of the preceding figures, the same reference numerals are used.

[0042] In Fig. Figure 8 shows the electronic torque wrench 10 in its locked home position. The release mechanism 28 is designed as a ball locking device 54. Several balls 56 are arranged in a ring around an axially displaceable release pin 58 and hold it in a defined position when locked. The balls 56 are located in radial bores or recesses of a sleeve or retaining element of the release mechanism 28 and, when locked, are supported outwards by the cylindrical outer surface of the release pin 58. The release pin 58 has a radially inwardly directed recess 60 in its central region, which, when locked, lies outside the effective range of the balls 56, so that the balls 56 are pressed outwards by the circumference of the release pin 58 and thus held in the locked position. A locking spring 59 pre-tensions the release pin 58.The locking spring 59 and the release pin 58 are guided in a bore 66 of the main actuating arm 20.

[0043] When the set target torque is reached, the solenoid 30 acts axially directly on the release pin 58 to move it in the direction of the balls 56. If the target torque has not yet been reached, the main actuating arm 20 remains fixed in its home position and blocked against movement by the locking mechanism of the balls 56. At the head region 16, the main actuating arm 20 rests against the cam surface 40 of the cam wheel 38 via the cam roller 42.

[0044] In Fig. Figure 9 shows the unlocked state after release. When the solenoid 30 is actuated, the release pin 58 is axially displaced so that the recess 60 enters the area of ​​the balls 56. The balls 56 can then move radially inwards into the recess 60, thus releasing the lock. As soon as the balls 56 enter the recess 60, the release pin 58 is released and the locking mechanism opens. The previously tensioned main actuating arm 20 is then moved over the cam surface 40 of the cam wheel 38. The cam roller 42 rolls over the rising section of the cam surface 40, passes over the apex of the cam 64, and then enters the falling section, thus completing the release stroke. After the overflow, the reset mechanism 62, which includes a return spring 44, causes the main actuating arm 20 to be returned to its locked initial position.

[0045] At the same time, the release pin 58 moves back to its starting position due to the restoring force of the locking spring 59 provided in the bore 66 for the release pin 58, thereby pushing the balls 56 outwards again and holding them in the locking position.

[0046] In Fig. 10 is the torque wrench 10 according to the Fig. 8 and Fig. Figure 9 shows the external structure. The lever housing 12 has the grip area 14 for force application and the head area 16 with the drive part 46, which carries an external square 48 onto which standardized sockets or wrenches can be placed. The adjustment mechanism 26 is located in the grip area 14 and is connected to the signal processing and control unit 24 via electrical lines. Inside the lever housing 12, as shown in the Fig. 8 and Fig.Figure 9 shows the lifting magnet 30, the release pin 58, the balls 56, the recess 60 and the main actuating arm 20 with cam roller 42 and cam wheel 38 arranged. Reference symbol list 10 Electronic torque wrenches 12 lever housings 14 Grip area 15 controls 16 Head area 20 Main actuation arm 22 Measuring sensor 24 Signal processing and control unit 26 Adjustment mechanism 28 Trigger mechanism 30 Lifting magnet 32 chain lock 33 bearing journals 34 Chain locking levers 36 chain links 38 Cam wheel 40 cam surface 42 Cam roller 44 Return spring 46 Drive unit 48 mm external square 50 locking mechanism 51 stage spring 52 Release duty 53 Backstage area 54 ball lock 55 Axial guide 56 balls 58 Release pin 59 Locking spring 60 Recess on the release pin 62 Return mechanism 64 Cam 66 Bore of the main actuating arm QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 20315000 U1

[0006] EP 3372344 A1

[0007] EP 3737533 B1

[0008] DE 20 2011 050 280 U1

[0009] DE 100 51 011 A1

[0010]

Claims

[1] Electronic torque wrench (10) for tightening screw connections with a predetermined nominal torque comprising a) a lever housing (12), b) a grip area (14) of the lever housing (12) for force application, c) a head area (16) with a drive part (46) for transmitting a torque to a workpiece, d) a main actuating arm (20) which is provided on the drive side in the lever housing (12), e) a measuring sensor (22) on the main actuating arm (20) and / or a bending element for detecting the applied torque, wherein the measuring sensor (22) outputs a signal corresponding to this torque to a signal processing and control unit (24), f) an adjustment mechanism (26) and / or adjustment electronics for setting the desired target torque, g) a release mechanism (28) for releasing the torque at the target torque, wherein the release mechanism (28) is controlled by the signal processing and control unit (24), characterized by , that h) the release mechanism (28) comprises a cam wheel (38) over whose cam (64) the main actuating arm (20) moves to release. [2] Electronic torque wrench (10) for tightening screw connections with a predetermined nominal torque according to claim 1, characterized by , that the cam wheel (38) is arranged in the drive part (46). [3] Electronic torque wrench (10) for tightening screw connections with a predetermined nominal torque according to one of claims 1 or 2, characterized by , that the release mechanism (28) comprises a lifting magnet (30) which acts directly or indirectly on the main actuating arm (20) via at least one further force transmission component. [4] Electronic torque wrench (10) for tightening screw connections with a predetermined nominal torque according to one of claims 1 to 3, characterized by , that the release mechanism (28) has an elastic return mechanism (62) by which the locking mechanism is returned to the locked initial position after release. [5] Electronic torque wrench (10) for tightening screw connections with a predetermined nominal torque according to one of claims 1 to 4, characterized by , that the main actuating arm (20) has a cam roller (42) at one end which is in contact with the cam wheel (38). [6] Electronic torque wrench (10) for tightening screw connections with a predetermined nominal torque according to one of claims 1 to 5, characterized by , that the measuring sensor (22) is designed as a strain gauge. [7] Electronic torque wrench (10) for tightening screw connections with a predetermined nominal torque according to one of claims 3 to 6, characterized by , that the release mechanism (28) comprises a chain lock (32) with two levers (34) mounted at the end of the main actuating arm (20) and two chain links (36) which are arranged in a substantially triangular position when locked, wherein the solenoid (30) acts on the chain links (36) to release, causing the triangular arrangement in the area of ​​the chain links (36) to buckle and the main actuating arm (20) to be released, thereby triggering the torque wrench (10). [8] Electronic torque wrench (10) for tightening screw connections with a predetermined nominal torque according to one of claims 3 to 6, characterized by, that the release mechanism (28) comprises a locking cam (50) which, in the locked state, blocks the movement of the main actuating arm (20) and is held in its position by a chain lock (32), wherein a lifting magnet (30) acts on the chain lock (32) so that it folds and releases the locking cam (50), thereby moving the main actuating arm (20) via the cam wheel (38) when released. [9] Electronic torque wrench (10) for tightening screw connections with a predetermined nominal torque according to one of claims 3 to 6, characterized by, that the release mechanism (28) comprises a ball locking mechanism (54) in which several balls (56) are arranged in a ring around a release pin (58) and hold it in position in the locked state, wherein the solenoid (30) moves the release pin (58) when actuated, so that the balls (56) move from their locking position into a radially inwardly directed recess (60) of the release pin (58) and release the locking mechanism, thereby moving the main actuating arm (20) via the cam wheel (38) when triggered.

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