SE1350328A1 - Motor-driven tool that delivers torque, with a flywheel and torque gauge - Google Patents

Abstract

P20-13702-130318 Abstract which for connection A power tool (10) for delivering a torque to a joint,(10) comprises an output shaft (19)to a screw or a nut of a joint and a motor (11)(12), (11) being arranged inside wherein the power tool comprises a power toolarranged todrive a motor shaft the motora tool housing (20),flywheel (22) tool housing, that may be driven to rotate with respect to theand which is arranged to take up at least partof the reaction forces sensed in the output shaft (19). A(34) is arranged at the output shaft (19) formonitoring the torque delivered by the power tool directly in the output shaft (19). torque meter (Elected for publication: Fig. 1)

Description

P20-13702-130318 Torque delivering power tool with fly wheel and torque meter The invention relates to a hand held power tool for deliveringtheinvention relates to a power tool with a reduced reaction a torque in order to tighten joints. Specifically, force.Background A hand held torque delivering power tool such as a nut runnerneeds to fulfil a number of criteria in order to make itefficient and agreeable to use for an operator. Firstly, itshould be adapted to provide a sufficiently high torque totighten a predetermined type of joints and it should beadapted to tighten said joint to a specific desired torque and /or clamp force.

Further, in order for the power tool to be agreeable to usefor an operator it should be light and the magnitude of thereaction forces that has to be counter acted by the operatorshould be kept as low as possible.

The reaction forces are produced as the screw or nut is beingtightened and the clamp force in the joint is produced. A nuttightening operation generally includes two phases, a firstphase during which the screw is threaded into the joint and asecond phase in which the screw is tightened and the clampforce in the joint is produced. The point in time where thethreading phase passes into the tightening phase is generallydenoted as ”snug”. It is only after snug, i.e. during thetightening phase that reaction forces will be created in the power tool. The reaction forces are created in response to theincreasing torque needed to tighten the joint by rotation of the screw.

A problem that needs to be addressed in most types of handheld torque delivering power tools is to keep the counterforces as low as possible, even when a considerable torque isapplied to the joint. A further object of torque deliveringpower tools is to provide a predetermined torque and/or clamp force to the joint to be tightened.

Conventionally, it may be difficult to achieve these two objects in one and the same power tool. Namely, if a power P20-13702-130318 tool includes some kind of arrangement to minimise thereaction forces in the power tool this arrangement will mostsuch that themeasured values thereof are less reliable than they would probably influence the measuring of the torque,otherwise be. Reliable torque values are needed to survey thetightening process and to tighten the joint to a specifictorque.

Therefore, there is a need for a power tool that produces low reaction forces, but which still provides a reliable monitoring of the delivered torque.Summary of the invention An object of the invention is to provide a hand held powertool in which the reaction forces that will be transmitted tothe operator will be kept as low as possible, but whichprovides a good reliability with respect to tightening jointsto a specific torque.

The invention relates to a hand held power tool for deliveringa torque to a joint, which power tool comprises an outputshaft for connection to a screw or a nut of a joint and amotor arranged to drive a motor shaft, the motor beingarranged inside a tool housing, wherein the power toolcomprises a flywheel that may be driven to rotate with respectto the tool housing, and which is arranged to take up at leastpart of the reaction forces sensed in the output shaft. A torque meter is arranged at the output shaft for monitoring the torque in the output shaft.

According to one embodiment of the invention the power toolcomprises a control unit for controlling the motor, whereinthe torque meter communicates the monitored torque to the control unit.

According to a specific embodiment of the invention a rotary transmitter is arranged at the output shaft, wherein a fixed transmitter is arranged opposed to the rotary transmitter, andwherein the rotary transmitter communicates with the fixed transmitter over a non-contact interface.

P20-13702-130318 According to another embodiment of the invention a slip ringis arranged to transfer the monitored torque from the outputshaft to the control unit.

In one embodiment of the invention the torque meter isarranged inside the output shaft.

In another embodiment of the invention the torque meter isarranged outside the output shaft and comprises strainmeasuring threads for measuring the torque in the outputshaft.

Preferred embodiments and other advantages of the inventionwill be apparent from the detailed description and from thedependent claims.

Short description of the drawings In the following detailed description reference is made to the accompanying drawings, of which: Fig. 1 shows a sectional view of a power tool according to afirst embodiment of the invention; Fig. 2 shows a detailed view of a part of fig. l; Fig. 3 shows a sectional view of a power tool according to asecond embodiment of the invention; Fig. 4 shows a detailed view of a part of fig. 3.

Detailed description of the shown embodiments of the invention Figure l shows a sectional view of a hand held power tool lOaccording to a first embodiment of the invention. The powertool lO comprises a motor ll, which is located inside ahousing 20 and which in the shown embodiment is an electricmotor.

Further, the power tool lO comprises a handle 25 and a trigger 26 for activation of the motor ll. which The planet Upon activation, the motor ll drives a motor shaft l2,is connected to a sun wheel l4 of a planet gear.gear further comprises a gear rim l5 and a number of planetwheels l6 which are arranged to rotate between the sun wheel l4 and the gear rim l5. The planet wheels l6 are P20-13702-130318 interconnected by means of a planet carrier 17 that isconnected to an output shaft 19.

As the power tool 10 is in operation to tighten a joint, e.g. when a screw is fastened to a nut, reaction forces that areproduced in the joint during the tightening operation will betransmitted from the output shaft 19 to the planet gear.

Conventionally, such reaction forces are transmitted from theplanet wheels 16 to the gear rim 15 and further to the power tool housing 20.

In the shown embodiment of the invention, the gear rim 15 is not fixed with respect to the housing. Instead, the gear rimsuch that Further, 15 is mounted in bearings 21, inside the housing 20,it may rotate freely with respect to the housing 20.a flywheel 22 is attached to the gear rim 15, such that it mayrotate along with the gear rim 15. The flywheel 22 comprises adisc shaped portion 29, which connect the flywheel 22 to the gear rim 15.

With this inventive arrangement, the gear rim 15 and theflywheel 22 will be set to rotate in response to the reactionforces from the output shaft 19.

Hence, theoretically no reaction forces will be transmitted to the tool housing, andno reaction forces will be transmitted tothe flywheel 22 will rotatefaster and faster as the reaction forces are transmitted fromthe output shaft 19 via the planet gear to the flywheel 22.

For a joint that yields a lot of reaction forces the flywheel 8.8 ö. COÛSGqUGDCG, the hand of the operator. Instead, 22 will eventually rotate at a relatively high speed.

A rotation lock 30 is arranged inside the tool housing to lockthe planet carrier 17 from rotation. The planet carrier 17 iswhen therotation lock 30 is activated, the planet carrier 17 and theoutput shaft 19 will be held still, provided by the motor shaft 12 will be transmitted from the rotatively connected to the output shaft 19. Hence, such that the rotationsun gear 14 via the planet wheels 16, which are allowed torotate around their own axes, to the gear rim 15 and theinterconnected flywheel 22.

The rotation lock 30 comprises a solenoid or an electromagnetwith an interaction surface 31 arranged to interact with atooth on an inner part 33 (see fig. 2) of the planet carrier P20-13702-130318 l7. This inner part 33 is preferably circular and ispreferably provided with several teeth arranged at evenintervals along its perimeter, such that the interactionsurface 3l of the solenoid or electromagnet will interact witha tooth regardless of the angular position of the planet carrier l7.

In order to monitor and control the torque delivered to thejoint the tool lO includes a torque meter 34 and a control unit 35.delivered to the joint and to transmit information of said is adapted to process the information about the torque and to control the The torque meter is arranged to monitor the torque torque to the control unit 35. The control unit 35 motor ll towards a target torque.

In conventional torque delivering power tools with a torquemeter the torque meter is arranged in a non-rotating part thatis supported by the housing. However, when a flywheel isarranged it will not be possible to obtain a fully reliablethe flywheel is up at least part of the reaction forces such that it will not value of the torque. Namely, arranged to takebe possible to measure a correct torque with respect to the housing. Therefore, the torque needs to be measured in an alternative manner.

In the power tool according to the invention the torque ismeasured at the output shaft l9. The torque meter 34 may comprise strain measuring threads that are arranged to measurethe torque in the output shaft l9. A complication that has tobe addressed when the torque is measured directly in the is theIn the first embodiment of the invention shown in figures l and 2 a output shaft, which of course rotates during operation, transmittal of the measured data from the output shaft. slip ring 36 is arranged to transmit the measured data fromthe output shaft to the control unit 35.further transmitted in wiresto the control unit 35.

The signals may be (not shown) from the slip ring 36 A second embodiment of the invention is shown in figures 3 and4. This embodiment is identical to the first embodiment exceptfor the transmitter pair for transmitting data from the outputshaft to the housing part. The power tool of the second embodiment includes rotary transmitter 37 that is arranged on the output shaft l9 and a fixed transmitter 38 that is P20-13702-130318 arranged opposed to the rotary transmitter 37.transmitter 37 communicates with the fixed transmitter 38 overa non-contact interface.

The rotary The art of transmitting data over anon-contact interface is in itself known from the Swedishpatent application SE l250444-5 which is hereby incorporatedby reference.

Above, specific embodiments of the invention have beendescribed. to either of these embodiments.

The scope of the invention is however not limitedInstead it is defined by thefollowing claims.

Claims (5)

Claims

1. A hand held power tool (10) for delivering a torque to a joint, which power tool (10) comprises an output shaft (19) for connection to a screw or a nut of a joint and a motor (11) 5 arranged to drive a motor shaft (12), the motor (11) being arranged inside a tool housing (20), wherein the power tool comprises a flywheel (22) that may be driven to rotate with respect to the tool housing, and which is arranged to take up at least part of the reaction forces sensed in the output 10 shaft (19), characterised in that a torque meter (34) is arranged -, sic, the output shaft (19) for monitoring the torque in the output shaft (19).

2. A power tool (10) according to claim 1, further comprising a control unit (35) for controlling the motor, 15 wherein the torque meter (34) communicates the monitored torque to the control unit (35).

3. A power tool (10) according to claim 2, wherein a rotary transmitter (37) is arranged at the output shaft (19) and a fixed transmitter (38) is arranged opposed to the rotary transmitter (37), and wherein the rotary transmitter (37) communicates with the fixed transmitter (38) over a non-contact interface.

4. A power tool (10) according to claim 2, wherein a slip ring (36) is arranged to transfer the monitored torque from the output shaft (19) to the control unit (35).

5. power tool (10) according to any of the claims 1-4, wherein the torque meter (34) is arranged outside the output shaft (19) and comprises strain measuring threads for measuring the torque in the output shaft (19). 19 34 12 21 16 36 22 11