Torque sensing unit for a power tool and a power tool comprising such a torque sensing unit
A torque sensing unit for a power tool arranged to generate a torque responsive signal by sensing the reaction torque transferred from a ring gear of a planetary reduction gearing to the tool housing. The torque sensing unit includes an annular torque transferring element disposed perpendicularly to the geometric axis of the ring gear and being formed with a first pair of external engagement portions for connecting the torque transferring element to the housing, a second pair of external engagement portions for connecting the torque transferring element to the ring gear, and at least one pair of weak elastically deformable zones located between the engagement portions and provided with sensors for delivering signals in response to the transferred reaction torque.
1. A torque sensing unit for a power tool having a housing, a rotation motor, and a planetary reduction gearing with a ring gear, the torque sensing unit comprising:
a torque transferring element interposed between the ring gear and the housing for transferring a reaction torque exerted on the ring gear to the housing, the torque transferring element including at least one strain sensor for delivering electric signals in response to the transferred reaction torque magnitude, and wherein:
the torque transferring element is substantially annular in shape and has an axial length substantially smaller than its radial dimensions,
the torque transferring element is arranged with its geometric axis coinciding with the geometric axis of the ring gear; and
wherein the torque transferring element further comprises:
a first pair of external engagement portions for co-operation with grooves in the housing;
a second pair of external engagement portions for co-operation with pockets in the ring gear, said first and second pairs of engagement portions being angularly spaced relative to each other; and
at least one pair of weak deformation zones located between said first and second pairs of engagement portions and arranged to be exposed to bend stresses by the reaction torque transferred by the torque transferring element, and wherein said at least one strain sensor is attached to one of said deformation zones.
2. The torque sensing unit according to claim 1 , wherein:
each one of said deformation zones comprises a flat surface extending in a plane substantially parallel with the geometric axis of the ring gear; and
said at least one strain sensor comprises a strain gauge mounted on said flat surface of at least one of said deformation zones.
3. The torque sensing unit according to claim 2 , wherein:
said at least one deformation zone comprises four deformation zones which are arranged in two pairs, with the deformation zones of one pair located diametrically opposite to the deformation zone of the other pair; and
said two pairs of deformation zones are located at a 90 degree angular spacing relative to each other.
4. The torque sensing unit according to claim 3 , wherein:
said engagement portions of said first pair are located diametrically opposite each other;
said engagement portions of said second pair are located diametrically opposite each other; and
the engagement portions of said first pair are angularly spaced from the engagement portions of said second pair by 90 degrees.
5. The torque sensing unit according to claim 4 , wherein said torque transferring element is a one-piece body.
6. The torque sensing unit according to claim 2 , wherein:
said engagement portions of said first pair are located diametrically opposite each other;
said engagement portions of said second pair are located diametrically opposite each other; and
the engagement portions of said first pair are angularly spaced from the engagement portions of said second pair by 90 degrees.
7. The torque sensing unit according to claim 6 , wherein said torque transferring element is a one-piece body.
8. The torque sensing unit according to claim 2 , wherein said torque transferring element is a one-piece body.
9. The torque sensing unit according to claim 3 , wherein said torque transferring element is a one-piece body.
10. The torque sensing unit according to claim 1 , wherein:
said at least one deformation zone comprises four deformation zones which are arranged in two pairs, with the deformation zones of one pair located diametrically opposite to the deformation zone of the other pair; and
said two pairs of deformation zones are located at a 90 degree angular spacing relative to each other.
11. The torque sensing unit according to claim 10 , wherein:
said engagement portions of said first pair are located diametrically opposite each other;
said engagement portions of said second pair are located diametrically opposite each other; and
the engagement portions of said first pair are angularly spaced from the engagement portions of said second pair by 90 degrees.
12. The torque sensing unit according to claim 11 , wherein said torque transferring element is a one-piece body.
13. The torque sensing unit according to claim 10 , wherein said torque transferring element is a one-piece body.
14. The torque sensing unit according to claim 1 , wherein:
said engagement portions of said first pair are located diametrically opposite each other;
said engagement portions of said second pair are located diametrically opposite each other; and
the engagement portions of said first pair are angularly spaced from the engagement portions of said second pair by 90 degrees.
15. The torque sensing unit according to claim 14 , wherein said torque transferring element is a one-piece body.
16. The torque sensing unit according to claim 1 , wherein said torque transferring element is a one-piece body.