SE538302C2 - Power wrench and a method of performing a tightening operation with such a power wrench - Google Patents

Abstract

Abstract A hand held power wrench including a housing (11) that houses a motor (12), an inertia body (13) that is driven by said motor, and an output shaft (14) for delivering a torque to joint and that extends outside of the housing. A first screw part (16) and a second screw part (17) are arranged and are mutually interconnected by means of a thread (18) that allows the first screw part (16) and the second screw part (17) to rotate with respect to each other between a first and a second end stop position, at which the first and second screw parts (16,17) are locked from mutual rotation in a first direction and second direction, respectively. Hence, the output shaft (14) will rotate with the inertia body (13) in a first direction in the first end stop position, and the first and second screw parts (16, 17) will rotate with the inertia body (13) in the opposite direction in the second end stop position.

Description

Power wrench and a method of performing a tightening operation with such a power wrench The invention relates to a hand held power wrench with a low reactionoperation. Specifically the invention relates to a power wrench that is capable of producing torque pulses of high precision.

Background Many industrial tightening operations are still performed by hand. Anoperator may perform several hundred tightening operations on aregular working day. It is hence important that these tighteningoperations may be performed with as little effort as possible and asergonomically advantageous as possible. An important factor for theergonomy of an operator of hand held torque wrench is the reactionforces that the operator has to withstand. The reaction forces should of course be kept as low as possible.

Different systems and power wrench arrangements exist for keeping thereaction forces at a low level. There are for instance pulsating toolsand there are tools with a very high rotational speed in combination with precise and sensitive control elements, in which the speed of the output shaft is continuously governed towards a target torque.

A problem in all methods of reaching a specific target torque in anergonomic manner is to achieve a good ergonomy while still achievingthe target torque in a precise manner. There may be a conflict inachieving both, since it may be needed to abruptly change the speed ofthe motor in order to govern the output shaft towards delivering a precise torque.

Hence, there is a need of a torque wrench capable of delivering a precise torque in a controlled and ergonomic manner.

Summary of the invention An object of the invention is to provide torque wrench that is capableof delivering a precise torque pulses in a controlled and ergonomicmanner. In this specification torque pulses are intended to signify atorque that is delivered during a limited period of time, as opposedto a continuous torque wrench. The invention is however not to be confounded with an impact wrench or a conventional impulse wrench.

According to a first aspect of the invention this object is achievedby hand held power wrench including: - a housing, - a motor located inside said housing, - an inertia body that is driven by said motor, - an output shaft for delivering a torque to a joint. The powerwrench further comprises a screw connection comprising a first screwpart and a second screw part that are mutually interconnected by meansof a thread that allows the first screw part and the second screw partto rotate with respect to each other up to a first end stop position at which the output shaft will be locked to rotate with the inertia body in a first direction.

The invention according to the first aspect provides a power wrenchthat is capable of delivering a high and precise torque with a low reaction force.

In one embodiment the first screw part and the second screw part arearranged to rotate with respect to each other between the first endstop position and a second end stop position, wherein the first andsecond screw parts are locked from mutual rotation in a seconddirection in the second end stop position such that the output shaftwill rotate with the inertia body in the first direction when thescrew connection is in the first end stop position and in the second direction when the screw connection is in the second end stop position.

In a specific embodiment of the invention the first screw part isconnected to the inertia body and is arranged in bearings with respectto the housing and wherein the second screw part is arranged totranslate axially with respect to the first screw part and comprises afirst and a second end stop, the first end stop position correspondingto a contact between the first end stop and a contact surface of thesecond screw part and the second end stop position corresponding to acontact between the second end stop and a contact surface of thesecond screw part, and wherein the second screw part is connected tothe output shaft via a splined connection, such that the second screwpart is allowed to move axially with respect to the output shaft but to rotate along with the same.

In another specific embodiment of the invention the first and thesecond end stops are arranged on opposite ends of the second screw part on opposite sides of the first screw part.

In yet another specific embodiment of the invention both end stops comprise an inner disc that is rotatably arranged with respect to thesecond screw part and arranged to face a contact surface on the firstscrew part, and an outer disc fixedly arranged on the second screwpart outside of the inner disc, which discs each comprise a recessed circumferential surface, respectively, that are arranged so as to face each other such that each pair of opposed recesses form a space, andwherein a roller is located in each space, and wherein the interactionbetween the recessed circumferential surfaces and the rollers limit the mutual rotation between the inner and the outer discs.

In another specific embodiment of the invention the inner disc of eachend stop is allowed to move axially within a gap, and wherein aresilient member is arranged to force the discs to rotate with respectto each other such that the recesses will be positioned out ofalignment with each other so as to force the inner disc axially away from the outer disc within said gap.

In one embodiment of the invention a torque sensor is arranged on the output shaft to measure the torque delivered by the output shaft.

According to a second aspect of the invention the above object isachieved by a method of performing a tightening operation or anuntightening operation with a hand held torque wrench as describedabove, the method comprising the steps of:- driving the motor in a first direction to create a span betweenthe first and second screw connection; - driving the motor in a second direction opposed to the firstdirection so as accelerate the inertia body and build up a rotational energy that is transmitted to the output shaft in a torque pulse when the screw connection reaches one of said end stops.

In a specific embodiment the method further comprises the steps ofmonitoring a parameter relating to the tightening or untighteningoperation, the parameter being the delivered torque, the angularposition of the output shaft or the clamp force installed into thejoint, wherein the method of driving the motor in a first and second direction is repeated until a target value has been reached.

Other features and advantages of the invention will be apparent from the figures and from the detailed description of the shown embodiment.

Short description of the drawings In the following detailed description reference is made to the accompanying drawings, of which: Fig. 1 shows a very schematic view of power wrench in accordance with an embodiment of the invention; Fig. 2 shows a sectional view of a screw connection of power wrench in accordance with a specific embodiment of the invention; Fig. 3 shows a sectional view of the screw connection of figure 2 in a first end position; Fig. 4 shows a sectional view of the screw connection of figure 2 in a second end position; and Fig. 5 shows a side view of an end stop of the screw connection of figures 2-4.

Detailed description of the shown embodiment of the invention In fig. 1 a schematic view of a handheld power wrench 10 according to a first embodiment of the invention is shown.

The power wrench 10 includes a housing 11 and a motor 12 locatedinside said housing. An inertia body 13 is arranged inside the housing11 and is drivingly connected to the motor 12. The power wrench 10 is provided with a power source 34, such as a battery, an electric connection or a connection to a pressurized air source, for drivingthe motor 12. A trigger 15 is arranged for activation of the motor 12.The power wrench 10 further comprises an output shaft 14 fordelivering a torque to a joint. A screw connection comprising a firstscrew part 16 and a second screw part 17 that are mutuallyinterconnected by means of a thread 18 is arranged. The first screwpart 16 is connected to the inertia body 13 and the motor 12, and theinertia body 13 may even be an integrated part of the motor 12 or thefirst screw part 16. The second screw part 17 is connected to theoutput shaft 14. The screw connection involves a first end stop 19 andin a corresponding first end stop position the first and second screwparts 16, 17 are locked from mutual rotation in a first direction suchthat the output shaft 14 is connected to the inertia body 13, via thescrew connection, such that it will rotate with the inertia body 13 when said screw connection is in the first end stop position.

Hence, in a general embodiment the power wrench may be arranged to deliver torque pulses in only one direction. Namely, in 99 per cent of the cases a power wrench is utilised to provide a tightening operationin clockwise direction.

Hence, a power wrench that is mainly arranged to provide a clockwise torque instalment is in most cases sufficient.

However, in the specifically shown embodiment below a bidirectional power wrench is illustrated.

In a preferred operation of the power wrench the inertia body isaccelerated by means of the motor l2. During the acceleration theoutput shaft l4 will remain still and the first screw part l6 willhence rotate with respect to the second screw part l7. As the firstscrew part l6 rotates in the first direction with respect to thesecond screw part l7 the first screw part l6 will move axially withrespect to the second screw part l7, to the left in figure l. At theend of the acceleration phase the first screw part l6 will reach thefirst end stop l9, whereupon further rotation of the first screw partl6 with respect to the second screw part l7 is prevented whereby theinertia that has been build up in the inertia body, the motor and thefirst screw part will be transmitted as a torque pulse to the secondscrew part l7 and hence to the output shaft l4, the second screw partl7 being rotatively connected to the output shaft l4. In the shownembodiment the second screw part l7 is integral with the output shaft l4.

A torque meter (not shown) and/or an angle encoder (not shown) may bearranged to monitor the torque and or angular span of the rotation ofthe output shaft l4 incurred by a torque pulse. The result of saidmonitoring may be used to control a tightening operation so that adesired torque, clamp force or angle is installed into the joint.

Hence, after a delivered torque pulse the installed torque, clampforce or angle may be evaluated and a new torque pulse may becommenced if a target value, such as a target torque, target clampforce or target angle has not been reached. Each following torquepulse will include the steps of reversing the first screw part l6 tosubsequently accelerating the first screw part l6 to a desired angularvelocity until it reaches the first end stop l9 to deliver anothertorque pulse to the joint via the output shaft l4. The procedure is repeated until the target value is reached. This may imply that the final torque pulse will be adjusted to deliver a torque pulse of a specific energy so as to not overshoot the desired target value.

In figure 2 a specific embodiment of the invention is shown in detail.In this specific embodiment the inertia body l3 is constructed as aflywheel that has a motor connection 20 for connection to a motorshaft (not shown). The inertia body l3 is connected to a first screw part l6. In the shown embodiment the first screw part l6 constitutesan outer part of the screw connection. The second screw part l7constitutes an inner part of the screw connection. The second screwpart l7 is formed as a sleeve that is connected to the output shaft l4via a splined coupling 2l and to the first screw part l6 via a thread l8 in the form of a ball screw connection.

The output shaft l4 is journalled in bearings 22 with respect to aninner part of the housing ll and is hindered from axial movement. Thefirst screw part l6 is journalled in bearings 23 with respect to thesame inner part of the housing ll and is also hindered from axialmovement. The second screw part l7 is hence arranged to translateaxially between the first end stop l9 and a second end stop 24. Due tothe two end stops l9 and 24 torque pulses may be delivered in bothdirections. A torque pulse is created by rotating the inertia body l3and the first screw part l6 in one direction, while holding the outputshaft l4 still in order to axially translate the second screw part l7towards one of the end stops and subsequently reversing the motor todrive the inertia body l3 and the first screw part l6 in the oppositedirection. The inertia body l3 and the first screw part l6 areaccelerated in said opposed direction until the second screw part l7reaches into contact with the end stop whereby a torque pulse is generated in the output shaft l4.

In figure 3 the second screw part l7 is in contact with the second endstop 24 and in figure 4 it is in contact with the first end stop l9.

The end stops are arranged on opposite ends of the second screw part 17 and are configured to withstand compression and to prevent locking of the second screw part 17 to either of the end stops 19, 24.

An end stop 24 is shown in detail in figure 5. The two end stops 19and 24 in figure 3 are identical but arranged in mirrored positions.In figure 5 the second end stop 24 is shown as example. The end stopcomprises two main parts 25 and 26. The first main part 25 is arrangedto face the first screw part 16 and has a contact surface 27 arrangedto be in contact with a contact surface 32 (see fig. 4) of the firstscrew part 16 when the second screw part 17 is in its end position.The second main part 26 of the end stop 24 constitutes the end portionof the second screw part 17. The two main parts 25 and 26 are arrangedsuch that a certain axial translation is allowed between them. 35 (see fig. 3) A gapis arranged in which the first main part 25 may moveboth axially and angularly. The main parts 25 and 26 each include arecessed circumferential surface 28 and 29, respectively, facing each other. Each pair of opposite recesses 28,29 forms a space in which aroller 30 is arranged. A plurality of such rollers 30 are evenly distributed between the two main parts 25 and 26. As a minimum, threerollers are arranged in just as many spaces formed by oppositerecesses. In the shown embodiment the main parts 25 and 26 each comprises twelve recesses, wherein twelve rollers are arranged, one in each space formed between two opposite recesses 28 and 29.

The end stop 24 is pre-stressed by means of resilient members 31, in the form of springs, towards an initial position, as shown in figure 5. The initial position makes sure that the rollers 30, when the endstop 24 is being pressed against the first screw part 16, will not be trapped in the deep of two opposite recesses. Namely, such position would complicate the returning of the end stop, since the rollerswould be trapped in said deep. By the action of the resilient memberssuch positioning will be avoided. When the end stop 24 will reach intocontact with the first screw part 16 the rotation of the end stop 24with respect to the first screw part 16 will be such that their contact will act on the first main part of the end stop 24 in the same direction as the resilient member 31. Hence, at this point the rollers30 will be pressed from both sides by the main parts 25 and 26 of theend stop 24. At the same time the first main part 25 will act in thesame direction as the resilient member 31 with respect to the secondthe side of the first main part 25 that is shown main part 26. Hence, in figure 5 will be pushed upwards, the second main part 26 beingfixedly arranged in the second screw part 17. The rollers 30 willtherefore interact with the curvature of the recesses so as to preventthe main parts 25 and 26 from further mutual rotation in the direction acted by the resilient member 31.

After a completed torque pulse when the output shaft 14, the motor 12and all the intermediate parts are at rest the end stop 24 will beprone to releasing rather than to remain locked. The first screw part16 will in this instance be located in the position shown in figure 3.When the motor starts to drive the inertia body 12 and the first screwpart 16 the first main part 25 of the end stop 24 will be driven in adownwards in direction releasing the pressure on the rollers 30, i.e. figure 5. Hence, the end stops are efficient in making sure that thescrew connection will not be locked in either end position. After aminor mutual rotation of the first screw part 16 and the end stop 24contact will be lost between the first screw part 16 and the contactsurface 27 of the end stop 24. Thereafter the second screw part 17 andthe end stop 24 will thread its way away from the first screw part 16towards the position in figure 5 where the opposite end stop 19 is in contact with the first screw part 16.

Both end stops 19 and 24 are of course arranged to function in the same manner, i.e. to allow the motor and inertia body to be connectedto the output shaft in a reliable manner but without risking to get stuck in a connective position.

Above, the invention has been described with reference to specificembodiments. The invention is however not limited to theseembodiments. It is obvious to a person skilled in the art that the invention comprises further embodiments within its scope of protection, which is defined by the following claims.

Claims (9)

538 302 Claims 1. A hand held power wrench (10) including: -a housing (11),

1. a motor (12) located inside said housing, -an inertia body (13) that is driven by said motor, 2. an output shaft (14) for delivering a torque to a joint, characterised in that the power wrench further comprises a screw connection comprising a first screw part (16) and a second screw part (17) that are mutually interconnected by means of a thread (18) that allows the first screw part (16) and the second screw part (17) to rotate with respect to each other up to a first end stop position at which the output shaft (14) will be locked to rotate with the inertia body (13) in a first direction.

2. The hand held power wrench (10) according to claim 1, wherein the first screw part (16) and the second screw part (17) are arranged to rotate with respect to each other between the first end stop position and a second end stop position, wherein the first and second screw parts (16, 17) are locked from mutual rotation in a second direction in the second end stop position such that the output shaft (14) will rotate with the inertia body (13) in the first direction when the screw connection is in the first end stop position and in the second direction when the screw connection is in the second end stop position.

3. The hand held power wrench (10) according to claim 2, wherein the first screw part (16) is connected to the inertia body (13) and is arranged in bearings (23) with respect to the housing (11) and wherein the second screw part (17) is arranged to translate axially with respect to the first screw part (16) and comprises a first and a second end stop (19,24), the first end stop position corresponding to a contact between the first end stop (19) and a contact surface (33) of the second screw part (17) and the second end stop position corresponding to a contact between the second end stop (32) and a 11 538 302 contact surface (32) of the second screw part (17), and wherein the second screw part (17) is connected to the output shaft (14) via a splined connection (21), such that the second screw part (17) is allowed to move axially with respect to the output shaft (14) but to rotate along with the same.

4. The hand held power wrench (10) according to claim 3, wherein the first and the second end stops (19,24) are arranged on opposite ends of the second screw part (17) on opposite sides of the first screw part (16).

5. The hand held power wrench (10) according to claim 4, wherein both end stops (19,24) comprise an inner disc (25) that is rotatably arranged with respect to the second screw part (17) and arranged to face a contact surface (32,33) on the first screw part (16), and an outer disc (26) fixedly arranged on the second screw part (17) outside of the inner disc (25), which discs (25,26) each comprise a recessed circumferential surface (28,29), respectively, that are arranged so as to face each other such that each pair of opposed recesses form a space, and wherein a roller (30) is located in each space, and wherein the interaction between the recessed circumferential surfaces (28,29) and the rollers (30) limit the mutual rotation between the inner and the outer discs (25,26).

6. The hand held power wrench (10) according to claim 5, wherein the inner disc (25) of each end stop (19,24) is allowed to move axially within a gap (35), and wherein a resilient member (31) is arranged to force the discs to rotate with respect to each other such that the recesses (28,29) will be positioned out of alignment with each other so as to force the inner disc (25) axially away from the outer disc (26) within said gap (35).

7. The hand held power wrench (10) according to anyone of the 30 preceding claims, wherein a torque sensor is arranged on the output shaft (14) to measure the torque delivered by the output shaft (14). 12 538 302

8. Method of performing a tightening operation or an untightening operation with a hand held power wrench according to anyone of the preceding claims, the method comprising the steps of: 1. driving the motor (12) in a first direction to create a span 5 between the first and second screw connection (16,17); 2. driving the motor in a second direction opposed to the first direction so as accelerate the inertia body (13) and build up a rotational energy that is transmitted to the output shaft in a torque pulse when the screw connection reaches an end stop (19,24).

9. The method according to claim 8, further comprising the steps of monitoring a parameter relating to the tightening or untightening operation, the parameter being the delivered torque, the angular position of the output shaft or the clamp force installed into the joint, wherein the method of driving the motor in a first and second direction is repeated until a target value has been reached. 13 538 302 I foljande bilaga finns en oversattning av patentkraven till svenska. Observera att det r patentkravens lydelse pa engelska som gaiter. A Swedish translation of the patent claims is enclosed. Please note that only the English claims have legal effect.