The present disclosure relates to an electric power tool for

tightening screw joints. In particular to an electric power tool with increased accuracy.

Background

In industrial use of torque delivering electric power tools such as power wrenches and nutrunners that are used for tightening joints it is important to monitor the applied torque in order to verify that the joints are fastened to a satisfactory degree. It is often desired to install a predetermined clamp force into a joint. Normally it is however difficult to monitor the clamp force and it is therefore common practice to instead control a tightening so as to install a specific target torque in a joint.

A difficulty related to the monitoring of a delivered torque is that there are losses due to friction in the joint and due to gear ripple and the like inside the tool that affects the accuracy of the

monitoring values in an unpredictable manner. The friction in a joint may vary largely between different joints, but it may be presumed to be constant for a specific joint at specific conditions, and there are manners of estimating the friction for a specific joint, both by empiric testing or by real time monitoring during the tightening of a j oint .

The variations that are due to gear ripple and the like inside the electric power tool are more difficult to predict. The variations that due to gear ripple also vary with the condition of the electric power tool. When the condition of the electric power tool is lowered the gear ripple of the electric power tool often increase.

Hence, there is a need of an improved electric power tool which is adapted to deliver a precise output torque and which is adapted to detect when the electric power tool need service.

Summary of the invention

An object of the invention is to provide an electric power tool for delivering a precise output torque with less variations due to gear ripple and the like. This object is achieved according to an exemplary embodiments of the present disclosure where the housing of the electric power tool encloses both a back torque transducer and a front torque transducer. The back torque transducer is provided on one side of the angle gear. And the front torque transducer is provided on the other side of the angel gear. By having two torque transducers, one on each side of the angel gear it is possible to get a more accurate torque result. This among others since the front torque transducer more accurately can measure the output torque on the output shaft. Thus, a first aspect of the present disclosure relates to an electric power tool for tightening screw joints. The electric power tool comprises a housing. The housing encloses an electric motor and an angle gear comprising an input bevel gear drivingly connected to the electric motor and an output bevel gear drivingly connected to an output shaft of the electric power tool. The housing further encloses a back torgue transducer arranged to measure a back torgue reaction value before the input bevel gear. The electric power tool further comprise a front torgue transducer arranged to measure a front torgue reaction value after the output bevel gear.

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 is a schematic view of an electric power tool 10 according to a specific embodiment of the invention. Detailed description of the shown embodiment of the invention

In fig. 1 an electric power tool 10 according to a specific embodiment of the invention is schematically shown. The electric power tool 10 comprises a housing 11. The housing 11 encloses an electric motor 12. The housing 11 further encloses an angle gear 17 comprising a input bevel gear 17a drivingly connected to the electric motor 12 and a output bevel gear 17b drivingly connected to an output shaft 16 of the electric power tool 10. The housing 11 yet further encloses a back torgue transducer 20 arranged to measure a back torgue reaction value before the input bevel gear 17a. Stated differently, in one

embodiment, the back torgue transducer 20 is arranged to measure the back torgue reaction value between the motor 12 and the the input bevel gear 17a. Also enclosed by the housing 11 is a front torgue transducer 21 arranged to measure a front torgue reaction value after the output bevel gear 17b. Stated differently, in one embodiment, the front torgue transducer 21 is arranged to measure the front torgue reaction value that is tranfered from the output bevel gear 17b.

A general idea according to exemplary embodiments of the present disclosure is to provide an electric power tool 10 were both the back torgue transducer 20 and the front torgue transducer 21 are enclosed in the housing 11. One advantage is that the electric power tool 10 can be made handheld since all the parts are encloses in the housing.

Another advantage by having all the elements enclosed in that housing 11 is easier installation and logistics since all the parts are enclosed in the housing 11.

The back torgue transducer 20 is provided on the back side of the angle gear 17. And the front torgue transducer 21 is provided on the front side of the angel gear 17. By having two torgue transducers 20, 21, one on each side of the angel gear 17, it is possible to get a more accurate torgue result. This among others since the front torgue transducer 21 more accurately can measure the output torgue on the output shaft 16. According to one exemplary embodiment of the present disclosure the electric power tool 10 is a hand held electric power tool 10.

According to one exemplary embodiment the housing 11 of the electric power tool 10 is shaped to be ergonomic to hold for an operator. An advantage with this embodiment is that the electric power tool 10 becomes more ergonomic. The risk for injuries of the operator is thereby reduced.

In one exemplary embodiment of the present disclosure the front torgue transducer 21 comprises a front torgue transferring element (not shown) arranged to transfer reaction torgue to the housing 11 and carrying front strain measuring sensors (not shown) arranged to generate a front torgue transducer value.

In yet another exemplary embodiment of the present disclosure the back torgue transducer 20 comprises a back torgue transferring element (not shown) arranged to transfer back reaction torgue to the housing 11 and carrying back strain measuring sensors (not shown) arranged to generate a back torgue transducer value.

In one exemplary embodiment of the present disclosure the electric power tool 10 comprises a back amplifier arranged to amplify the back torgue transducer value and arranged close to the back strain

measuring sensors .

According to one exemplary embodiment of the present disclosure the electric power tool 10, further comprises a front amplifier arranged to amplify the front torgue transducer value and arranged close to the front strain measuring sensors.

According to another exemplary embodiment of the present disclosure the electric power tool 10 is further operative to terminate a tightening when the front torgue transducer value and the back torgue transducer value exceeds a torgue difference limit, where the torgue difference limit is the difference between the front torgue transducer value and the back torgue transducer value .

In yet another exemplary embodiment of the present disclosure the electric power tool 10 is further operative to retrieve the torgue difference limit. The present disclosure further relates to an electric power tool controller (not shown) configured to control the electric power tool 10 according to any of the described exemplary embodiments.

In one exemplary embodiment of the present disclosure the electric power tool controller is operative to control a tightening performed by the electric power tool 10 based on the front torgue transducer value or the back torgue transducer value and monitor the tightening based on the front torgue transducer value or the back torgue

transducer value not used to control the tightening. According to another exemplary embodiment of the present disclosure the electric power tool controller is further operative to terminate a tightening when the front torgue transducer value and the back torgue transducer value exceeds a torgue difference limit, where the torgue difference limit is the difference between the front torgue transducer value and the back torgue transducer value .

In yet another exemplary embodiment of the present disclosure the electric power tool controller is further operative to retrieve the torgue difference limit.

According to another exemplary embodiment of the present disclosure the electric power tool further comprises the electric power tool controller according to any of the described embodiments .

The present disclosure also relates to a computer readable storage medium comprising a computer program which when run in the electric power tool controller causes the electric power tool controller to be operative according to any of the described embodiments .

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.