WO2016091403A1

WO2016091403A1 - Power wrench and a method of performing a tightening operation with such a power wrench

Info

Publication number: WO2016091403A1
Application number: PCT/EP2015/068283
Authority: WO
Inventors: Karl Johan Lars Elsmark; Robin McGOUGAN
Original assignee: Atlas Copco Industrial Technique Ab
Priority date: 2014-12-10
Filing date: 2015-08-07
Publication date: 2016-06-16
Also published as: SE538302C2; SE1451506A1

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 reaction operation. Specifically the invention relates to a power wrench that is capable of producing torgue pulses of high precision.

Background

Many industrial tightening operations are still performed by hand. An operator may perform several hundred tightening operations on a regular working day. It is hence important that these tightening operations may be performed with as little effort as possible and as ergonomically advantageous as possible. An important factor for the ergonomy of an operator of hand held torgue wrench is the reaction forces 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 the reaction forces at a low level. There are for instance pulsating tools and 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 torgue.

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

Hence, there is a need of a torgue wrench capable of delivering a precise torgue in a controlled and ergonomic manner. Summary of the invention

An object of the invention is to provide torque wrench that is capable of delivering a precise torque pulses in a controlled and ergonomic manner. In this specification torque pulses are intended to signify a torque that is delivered during a limited period of time, as opposed to 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 achieved by 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 power wrench further comprises a screw connection comprising a first screw part and a second screw part that are mutually interconnected by means of a thread that allows the first screw part and the second screw part to 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 wrench that 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 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 are locked from mutual rotation in a second direction in the second end stop position such that the output shaft will rotate with the inertia body 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 . In a specific embodiment of the invention the first screw part is connected to the inertia body and is arranged in bearings with respect to the housing and wherein the second screw part is arranged to translate axially with respect to the first screw part and comprises a first and a second end stop, the first end stop position corresponding to a contact between the first end stop and a contact surface of the second screw part and the second end stop position corresponding to a contact between the second end stop and a contact surface of the second screw part, and wherein the second screw part is connected to the output shaft via a splined connection, such that the second screw part 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 the second 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 the second screw part and arranged to face a contact surface on the first screw part, and an outer disc fixedly arranged on the second screw part 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, and wherein a roller is located in each space, and wherein the interaction between 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 each end stop is allowed to move axially within a gap, and wherein a resilient member is arranged to force the discs to rotate with respect to each other such that the recesses will be positioned out of alignment 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 torgue delivered by the output shaft.

According to a second aspect of the invention the above object is achieved by a method of performing a tightening operation or an untightening operation with a hand held torgue wrench as described above, the method comprising the steps of:

driving the motor in a first direction to create a span between the first and second screw connection;

driving the motor in a second direction opposed to the first direction so as accelerate the inertia body and build up a rotational energy that is transmitted to the output shaft in a torgue pulse when the screw connection reaches one of said end stops.

In a specific embodiment the method further comprises the steps of monitoring a parameter relating to the tightening or untightening operation, the parameter being the delivered torgue, 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.

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 located inside said housing. An inertia body 13 is arranged inside the housing 11 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 driving the motor 12. A trigger 15 is arranged for activation of the motor 12. The power wrench 10 further comprises an output shaft 14 for

delivering a torgue to a joint. 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 is arranged. The first screw part 16 is connected to the inertia body 13 and the motor 12, and the inertia body 13 may even be an integrated part of the motor 12 or the first screw part 16. The second screw part 17 is connected to the output shaft 14. The screw connection involves a first end stop 19 and in a corresponding first end stop position the first and second screw parts 16, 17 are locked from mutual rotation in a first direction such that the output shaft 14 is connected to the inertia body 13, via the screw 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 torgue pulses in only one direction. Namely, in 99 per cent of the cases a power wrench is utilised to provide a tightening operation in clockwise direction. Hence, a power wrench that is mainly arranged to provide a clockwise torgue 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 is accelerated by means of the motor 12. During the acceleration the output shaft 14 will remain still and the first screw part 16 will hence rotate with respect to the second screw part 17. As the first screw part 16 rotates in the first direction with respect to the second screw part 17 the first screw part 16 will move axially with respect to the second screw part 17, to the left in figure 1. At the end of the acceleration phase the first screw part 16 will reach the first end stop 19, whereupon further rotation of the first screw part

16 with respect to the second screw part 17 is prevented whereby the inertia that has been build up in the inertia body, the motor and the first screw part will be transmitted as a torque pulse to the second screw part 17 and hence to the output shaft 14, the second screw part

17 being rotatively connected to the output shaft 14. In the shown embodiment the second screw part 17 is integral with the output shaft 14.

A torque meter (not shown) and/or an angle encoder (not shown) may be arranged to monitor the torque and or angular span of the rotation of the output shaft 14 incurred by a torque pulse. The result of said monitoring may be used to control a tightening operation so that a desired torque, clamp force or angle is installed into the joint.

Hence, after a delivered torque pulse the installed torque, clamp force or angle may be evaluated and a new torque pulse may be

commenced if a target value, such as a target torque, target clamp force or target angle has not been reached. Each following torque pulse will include the steps of reversing the first screw part 16 to subsequently accelerating the first screw part 16 to a desired angular velocity until it reaches the first end stop 19 to deliver another torque pulse to the joint via the output shaft 14. 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 13 is constructed as a flywheel that has a motor connection 20 for connection to a motor shaft (not shown) . The inertia body 13 is connected to a first screw part 16. In the shown embodiment the first screw part 16 constitutes an outer part of the screw connection. The second screw part 17 constitutes an inner part of the screw connection. The second screw part 17 is formed as a sleeve that is connected to the output shaft 14 via a splined coupling 21 and to the first screw part 16 via a thread 18 in the form of a ball screw connection.

The output shaft 14 is journalled in bearings 22 with respect to an inner part of the housing 11 and is hindered from axial movement. The first screw part 16 is journalled in bearings 23 with respect to the same inner part of the housing 11 and is also hindered from axial movement. The second screw part 17 is hence arranged to translate axially between the first end stop 19 and a second end stop 24. Due to the two end stops 19 and 24 torque pulses may be delivered in both directions . A torque pulse is created by rotating the inertia body 13 and the first screw part 16 in one direction, while holding the output shaft 14 still in order to axially translate the second screw part 17 towards one of the end stops and subsequently reversing the motor to drive the inertia body 13 and the first screw part 16 in the opposite direction. The inertia body 13 and the first screw part 16 are accelerated in said opposed direction until the second screw part 17 reaches into contact with the end stop whereby a torque pulse is generated in the output shaft 14.

In figure 3 the second screw part 17 is in contact with the second end stop 24 and in figure 4 it is in contact with the first end stop 19. 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 19 and 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 stop comprises two main parts 25 and 26. The first main part 25 is arranged to face the first screw part 16 and has a contact surface 27 arranged to be in contact with a contact surface 32 (see fig. 4) of the first screw 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 portion of the second screw part 17. The two main parts 25 and 26 are arranged such that a certain axial translation is allowed between them. A gap 35 (see fig. 3) is arranged in which the first main part 25 may move both axially and angularly. The main parts 25 and 26 each include a recessed circumferential surface 28 and 29, respectively, facing each other. Each pair of opposite recesses 28,29 forms a space in which a roller 30 is arranged. A plurality of such rollers 30 are evenly distributed between the two main parts 25 and 26. As a minimum, three rollers are arranged in just as many spaces formed by opposite recesses. 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 end stop 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 rollers would be trapped in said deep. By the action of the resilient members such positioning will be avoided. When the end stop 24 will reach into contact with the first screw part 16 the rotation of the end stop 24 with 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 rollers 30 will be pressed from both sides by the main parts 25 and 26 of the end stop 24. At the same time the first main part 25 will act in the same direction as the resilient member 31 with respect to the second main part 26. Hence, the side of the first main part 25 that is shown in figure 5 will be pushed upwards, the second main part 26 being fixedly arranged in the second screw part 17. The rollers 30 will therefore interact with the curvature of the recesses so as to prevent the main parts 25 and 26 from further mutual rotation in the direction acted by the resilient member 31.

After a completed torgue pulse when the output shaft 14, the motor 12 and all the intermediate parts are at rest the end stop 24 will be prone to releasing rather than to remain locked. The first screw part 16 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 screw part 16 the first main part 25 of the end stop 24 will be driven in a direction releasing the pressure on the rollers 30, i.e. downwards in figure 5. Hence, the end stops are efficient in making sure that the screw connection will not be locked in either end position. After a minor mutual rotation of the first screw part 16 and the end stop 24 contact will be lost between the first screw part 16 and the contact surface 27 of the end stop 24. Thereafter the second screw part 17 and the end stop 24 will thread its way away from the first screw part 16 towards 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 connected to 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 specific embodiments. The invention is however not limited to these

embodiments. 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

1. A hand held power wrench (10) including:

a housing (11) ,

a motor (12) located inside said housing,

- an inertia body (13) that is driven by said motor,

an output shaft (14) for delivering a torgue 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 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 preceding claims, wherein a torgue sensor is arranged on the output shaft (14) to measure the torgue delivered by the output shaft (14) .

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:

driving the motor (12) in a first direction to create a span between the first and second screw connection (16,17);

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 torgue 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 torgue, 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.