ELSMARK, Karl, Johan, Lars (Ättiksvägen 6, Saltsjö-Boo, S-132 39, SE)
| Claims . 1. Portable power wrench comprising a housing (10,11), a motor, an output shaft (21), a power transmission including a drive spindle (15) and coupling the motor to the output shaft (21), a torque sensor (27), and a signal receiving device located in the housing (10,11) and communicating with the torque sensor (27), c h a r a c t e r i z e d in that • the drive spindle (15) comprises a weak portion (26) elastically deformable by the transferred torque and carrying the torque sensor (27), • the drive spindle (15) is formed with an internal cavity (30) , • a signal treating circuitry (28) connected to the torque sensor (27) and confined within said cavity (30) , and • a contact free signal transferring means (35) arranged to transfer signals between said signal treating circuitry (28) in the drive spindle cavity (30) and the signal receiving device in the housing (10,11) . 2. Power wrench according to claim 1, wherein the housing (10,11) comprises a main section (10), and a front section (11), the drive spindle (15) is rotatively journalled in said front section (11), and said contact free signal transferring means (35) is arranged to transfer signals as well as electric power between the drive spindle (15) and said main section (10) . 3. Power wrench according to claim 2, wherein said front section (11) forms a separate unit detachably mounted on the main section (10), and said front section (11) is provided with a gearing (19,20) with a certain gear ratio, wherein said front section (11) is one of a number of exchangeable units with different gear ratios. 4. Power wrench according to claim 3, wherein said gearing (19,20) comprises an angle gear (18) coupling the drive spindle (15) to the output shaft (21) . 5. Power wrench according to anyone of claims 1-4, wherein said drive spindle (15) has a rear end portion (25) extending into the main section (10), and said contact free signal transferring device (35) comprises a stationary part (36) mounted in said main section (10) and a rotating part (37) connected to the drive spindle (15) . |
The invention relates to a portable power wrench including a housing, a motor, a torque delivering output shaft, a power transmission including a torque transferring drive spindle, a torque sensor arranged to deliver signals in response to the magnitude of the delivered output torque, and a signal receiving device communicating with the torque sensor .
In power wrenches of the above mentioned type there is a desire to locate the torque sensor as close as possible to the output shaft to get a torque responsive signal with as small deviations as possible from the actually delivered output torque magnitude and without disturbances from reduction gearings. This means that the torque sensor should be located in the front section of the wrench housing, on or close to the output shaft. In some
previously known wrench designs the torque sensor has actually been located on the output shaft, but the drawback of such an arrangement is added dimensions of the output end of the wrench resulting in an impaired accessibility of the wrench in cramped areas. On the other hand it has been difficult to find a space inside the housing for locating the torque sensor in a position well protected from
external disturbances and without adding in a negative way to the outer dimensions of the wrench.
Another problem is related to the above type of power wrenches having a front section which includes not only a torque sensor but a gearing, for instance an angle gear, and/or some other functional means that may be specific for certain power wrench applications and which would be exchangeable for adapting the wrench to different
application. This is usually obtained by exchanging the entire front section of the wrench housing for another front section comprising a different gearing and/or other features. In this type of tools the torque sensor usually communicates signals to a signal treating circuitry in the main part of the wrench housing for further transmittance to a control unit, and when exchanging the front section of the housing the connections between the sensor in the front section of the housing and the circuitry in the main part of the housing have to be disconnected and reconnected. Normally, this requires a certain time and effort and has a negative effect on the productivity of the wrench. It is an object of the invention to provide an improved power wrench by which the above problems are solved by arranging not only a torque sensor but a torque signal treating circuitry in association with the drive spindle inside the front section of the wrench housing thereby getting a reliable torque signal, a compact wrench design.
It is a further object of the invention to provide an improved power wrench with a torque sensor and signal treating circuitry located in association with the drive spindle inside the front section of the wrench housing, and including means for a wireless communication of signals between the signal treating circuitry and a control unit, whereby is accomplished an easy way of changing front sections and adapting the wrench to different applications without time consuming wire disconnections and
reconnections . Further objects and advantages of the invention will appear from the following specification and claims.
A preferred embodiment of the invention is described below with reference to the accompanying drawing.
In the drawing
Fig. 1 shows a side view of a portable power wrench
according to the invention.
Fig. 2 shows a longitudinal section through the forward end of the power wrench in Fig. 1.
The illustrated power wrench is of an electric angle type which comprises a straight housing with a main section 10, a front section 11, and a rear handle 12 carrying a power control lever 13. In the main section 10 there is supported a non-illustrated rotation motor which via a reduction gearing 14 is coupled to a drive spindle 15 rotatively supported in the front section 11 by a ball bearing 16 and a needle bearing 17, and the drive spindle 15 extends by a rear end portion 25 into the main section 10 of the
housing. At its forward end the drive spindle 15 is formed with a pinion gear 19 which is arranged to engage a bevel gear 20 on an output shaft 21 to form an angle gear 18. The output shaft 21 extends in a right angle to the drive spindle 15 and is formed with a square end 22 for carrying a nut socket. The output shaft 21 is supported relative to the front section 11 of the housing via a ball bearing 23 and needle bearing 24.
The front section 11 of the housing is detachably connected to the main section 10 via threaded connection of a
conventional design, and the interface between the front section 11 and the main section 10 is illustrated by a thickened line A-A. An advantageous feature of the power wrench according to the invention is that the front section 11 may easily be exchanged for another one of a number of front sections having identical interface relative to the main section 10 but having different characteristics for adapting the power wrench to different applications. The difference in characteristics may relate to alternative angle drive gear ratios, provision of an angle head or not, and alternative sensors for torque and rotation angle.
The drive spindle 15 is formed with a weakened portion 26 which is elastically deformable to the torque transferred by the drive spindle 15 and which is provided with a torque sensor 27 in the form of a set of strain gauges. Moreover, the drive spindle 15 comprises a coaxially extending internal cavity 30 enclosing a signal treating circuitry 28 connected to the torque sensor 27. This connection is accomplished by a non-illustrated electric leads extending through the cavity 30 and a radial aperture 31 in the drive spindle 15. A wiring 32 extends rearwardly through a coaxial extension 33 of the cavity 30, out through a radial opening 34 for connecting the circuitry 28 to a contact free signal transferring device 35 at the interface A-A between the main section 10 and the front section 11 of the housing. The contact free device 35 comprises an induction device having a stationary part 36 supported on the main section 10 of the housing and a rotating part 37 supported on a flange 38 mounted on the rear end portion 25 of the drive spindle 15.
The signal transferring device 35 is provided for
transferring electric signals between the rotating signal treating circuitry 28 in the front section 11 of the housing, and a non-illustrated signal receiving device in the main section 10 of the housing. The signal transferring device 35 is arranged to transfer some electric power as well, because a certain amount of electric power has to be supplied to activate the torque sensor 27.
The signal receiving device in the main section of the housing includes digitalizing means and communicates with a process control unit 40 which is located at a distance from the power wrench, wherein the communication between the signal receiving device in the power wrench housing and the control unit may be performed via a cable 41, as
illustrated in Fig. 1, or via a radio frequency
communication.
In the illustrated embodiment of the invention the signal and power transferring device 35 comprises an inductive device. However, the invention is not restricted to this particular type of device but may include other types of available devices for contact free transmission of electric power and signals. A contact free transmission device is advantageous by being independent of mechanical contacts which are sensitive to oxide and/or dirt. A contact free transmission device is advantageous also by facilitating exchange of front sections.
It is to be understood that the invention is not restricted to the above described example but may be freely varied within the scope of the claims.