Torque sensing unit for a power tool and a power tool comprising such a torque sensing unit

(54) Title: Torque sensing unit for a power tool (56) Published publications: WO 2008090069 Al · US 4404799 A (47) Abstract:

A torque sensing unit for a power tool arranged to deliver a torque-related signal by sensing the reaction torque transmitted from the gear ring in a planetary-type reduction gear (12) to the tool housing (10), the torque sensing unit (20) comprising an annular torque transmitting element (22) arranged perpendicular to the geometric axis of the gear ring (16) and formed with a first pair of external engagement portions (24,25) for interconnecting the torque transmitting element (22) with the housing (10), and a second pair of external engagement portions (27,28) for interconnecting the torque transmitting element (22) with the gear ring (16), and at least one pair of elastically deformable zones (42a-d) located between the engaging portions (24,25,27,28) and provided with sensors (43) for delivering signals corresponding to the transmitted reaction torque.

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Summary

A torque sensing unit for a power tool arranged to deliver a torque-related signal by sensing the reaction torque transmitted from the gear ring in a planetary-type reduction gear (12) to the tool housing (10), the torque sensing unit (20) comprising an annular torque transmitting element (22) arranged perpendicular to the geometric axis of the gear ring (16) and formed with a first pair of external engagement portions (24,25) for interconnecting the torque transmitting element (22) with the housing (10), and a second pair of external engagement portions (27,28) for interconnecting the torque transmitting element (22) with the gear ring (16), and at least one pair of elastically deformable zones (42a-d) located between the engaging portions (24,25,27,28) and provided with sensors (43) for delivering signals corresponding to the transmitted reaction torque.

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Torque sensing unit for a power tool

The present invention relates to a torque sensing unit for a power tool in which a signal corresponding to the delivered torque is generated by sensing the reaction torque transmitted from a part of a reduction gear to the tool housing.

In particular, the invention relates to a torque sensing unit comprising a reaction torque transmitting element connected between a gear ring in a reduction gear and the tool housing and provided with load sensors arranged to emit signals corresponding to the transmitted reaction torque and the delivered torque from the tool.

A prior art type of torque sensing means is disclosed in, for example, US 4,620,449 and contains an elastically deformable sleeve which connects a gear ring of the reduction gear to the tool housing, and a strain type strain sensor arranged to indicate elastic torsional deformation of the sleeve corresponding to the reaction sleeve as the reaction sleeve. This device is disadvantageous in that it requires a substantial axial space in the tool housing. It is also relatively expensive to manufacture.

Another type of torque sensing means for torque releasing tools is described in US 5,172,774. This known torque sensing device comprises a wheel-shaped torque transmitting element comprising a hub provided with splines for connection with a fixed disk mounted in the housing, and a peripheral portion formed with external splines.

534 852 for coupling with a gear element subjected to reaction torque. This device is advantageous in that it requires a relatively small axial space in the tool housing, but instead requires a large radial space and is quite complicated and expensive to manufacture.

It is a principal object of the invention to provide an improved torque sensing unit for a power tool, thereby avoiding the disadvantages of prior art devices. The invention thus aims to create a torque sensing unit for a power tool which is compact and inexpensive to manufacture.

Further advantages and objects of the invention will be apparent from the following description and claims.

A preferred embodiment of the invention is described in detail below with reference to the accompanying drawing.

drawings

Fig. 1 shows a longitudinal section through a power tool comprising a torque sensing unit according to the invention. Fig. 2 shows a cross section along line II-II of Fig. 1.

Fig. 3 is a perspective view of a torque transmitting element according to the invention comprising a load sensing means.

The power tool shown in the drawings is a nut driver for tightening screw joints and comprising a housing 10, a rotary motor 11, a reduction gear 12, and an output shaft 13 stored in an angular head 14. The reduction gear 12 comprises two planetary gear stages of a well-known type. series and

534 852 having a common non-rotating gear ring 16 connected to housing 10. In order to maintain the scope of the description, the planetary gear stages are not described in further detail. However, the reduction gear 12 has a primary drive shaft which is formed with a sun gear 19 and connected to the engine 11.

The gear ring 16 is connected to the housing 10 via a torque-sensing unit 20 which is arranged to transmit to the housing 10 the reaction torque exerted on the gear ring 16 during the work of the tool.

As is well known in the prior art, the reaction torque transmitted via the gear gear's gear ring is proportional to the delivered torque on the output shaft of the tool, and in order to provide a stationary and relatively simple device for measuring the torque delivered by the tool, a torque sensing means has been arranged between gear ring and tool housing. As described above, prior art devices for this purpose have been disadvantageous by requiring too much space and / or being too complicated and expensive to manufacture.

In the power tool illustrated in the drawings, a torque sensing unit 20 with an annular torque transmitting element 22 is arranged between the gear ring and the housing 10 and has a geometric axis that coincides with the geometric axis of the gear ring 16. This torque transmitting element 22 is relatively thin, i.e. its axial length is substantially smaller than its radial dimensions, which means that it requires only a limited axial space in the housing 10. The torque transmitting element 22 is formed with a first pair of external and

534 852 diametrically opposed engagement portions 24.25 for connection to housing 10, and a second pair of diametrically opposed engagement portions 27.28 for connection to the gear ring 16. The first pair of engagement portions 24.25 are angularly displaced 90 degrees to the second pair of engagement portions 27.28.

The first pair of engagement portions 24.25 is intended to transmit reaction forces F_R from the torque transmitting element 22 to the housing 10, while the second pair of engaging portions 27,28 are intended to transmit torque-related tangentially directed forces F_T received from the gear ring 16 to the torque transmitting element 22. See Fig. 3.

The engaging portions 24,25 of the first pair are arranged to be included in grooves 31,32 of the housing 10, and the engaging portions 27,28 of the second pair are arranged to be received in pockets 36,37 of the gear ring 16. See Fig. 2.

Between the first and second pairs of engagement portions 24,25 and 27,28 respectively, four identical soft zones 42 ad are found which, during torque transfer, are subjected to bending stresses and thus become elastically deformed. To measure this deformation caused by bending stresses, strain gauges 43 are provided, only one of which is illustrated in Fig. 3. These strain gauges 43 are mounted on flat surfaces 45 ad extending in planes A and B parallel to the geometric axis C. of the gear ring 16. In the transverse direction, these planes A and B extend along chord lines through an imaginary circle which is concentric to the gear ring 16.

Each strain transducer 43 is suitably connected to a Wheatstone bridge in a work control or monitoring unit.

534 852 device placed on board the tool or at a distance from the tool as a stationary unit, whereby torque-related signals are provided to indicate the torque delivered from the tool. By comparing the current signals with preset signals representing a desired final torque level, it is possible to determine when the delivered torque has reached a desired level and if desired initiate an automatic shutdown of the tool.

Due to its compact dimensions and its simple design, the torque sensing unit according to the invention is not only suitable for but specially adapted for use in power tools. The annular torque transmitting element 22 can be produced rationally by extrusion technique where, for example, a light metal tubular member of the desired cross-sectional form is extruded, and separate elements are created by cutting the blank into sheets.

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