Patent Publication Number: US-8991518-B2

Title: Portable power wrench with a gear casing and a parameter sensing device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a portable power wrench comprising a housing with a rotation motor, a gear casing including a gearing and an output shaft, wherein the gear casing is rotatively and/or releasably connected to the housing via a swivel or multi-position connection. 
     In particular the invention concerns a power wrench of the above type wherein at least one operation parameter sensing device is located in the gear casing and connected to an operation control unit, and a means for transferring signals between the operation parameter sensing means in the gear casing and the housing. 
     2. Description of the Related Art 
     In power wrenches provided with operation parameter sensing devices like torque transducers it is an advantage from the signal accuracy point of view to locate the torque transducer as close as possible to the screw joint being tightened, e.g. on the output shaft of the power wrench or at least on a rotating part in the gear casing. This is a previously well known want. It is also previously known to have sensing means activating power as well as generated signals transferred between the sensing means and the wrench housing via different types of signal transferring means. 
     A particular signal transmission problem occurs in power wrenches having a forward gear casing that is rotatively and/or releasably supported on the power wrench housing via a swivel or multi-position connection. A power wrench of this type is previously described in for instance U.S. Pat. No. 4,485,698. When such a power wrench is provided with one or more operation parameter sensing devices located in the gear casing the signals generated thereby have to be transferred from the gear casing to an electronic operation control unit which is provided either in the tool housing or in a stationary unit separate from the power wrench. In both cases there is a requirement to obtain a simple yet reliable transfer of signals from the sensing device or devices in the gear casing to a wiring in the housing for further transport to a control unit, in the housing or at a remote location. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a portable power wrench comprising a housing, a gear casing rotatively and/or releasably supported on the housing via a swivel or multi-position connection, wherein the gear casing comprises at least one power transferring rotating part, and at least one operation parameter sensing device, and movement admitting signal transferring devices provided to transfer operation parameter related signals generated by the sensing device or devices to the gear casing and the wrench housing. 
     It is another object of the invention to provide a portable power wrench comprising a housing, a gear casing rotatively and/or releasably supported on the housing via swivel connection, wherein the gear casing comprises at least one power transferring rotating part, and at least one operation parameter sensing device associated with the power transferring rotating part, and a contact free movement admitting signal transferring device arranged between the rotating part and the gear casing. 
     Still another object of the invention is to provide a portable power wrench comprising a housing, a gear casing rotatively and/or releasably supported on the housing and comprising a power transferring rotating part, at least one operation parameter sensing device associated with the power transferring rotating part, and signal treating electronic components connected to the sensing device, wherein the power transferring rotating part is formed with a coaxial cavity in which the electronic components are located. 
     Further objects and advantages of the invention will appear from the following specification and claims. 
     Preferred embodiments of the invention are described below with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a side view of a power wrench according to the invention. 
         FIG. 2  shows a longitudinal section through the gear casing of the power wrench in  FIG. 1 . 
         FIG. 3  shows a longitudinal section through the gear casing of a power wrench according to an alternative embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The power wrench illustrated in  FIGS. 1 and 2  comprises a housing  10  with a rear handle  11  and a motor section  12  extending substantially in parallel with the handle  11  and enclosing a rotation motor. A gear casing  15  is rotatively and releasably connected to the housing  10  and carries a torque reaction bar  16  at its forward end. The torque reaction bar  16  is supported and rotationally locked relative to the gear casing  15  via a splines portion  17 . The interface between the housing  10  and the gear casing  15  is illustrated by a line A-A. 
     The gear casing  15  is axially locked relative to the housing  10  in a conventional way by balls  26  engaging grooves in the two parts, and a maneuver sleeve  27  is movably supported on the housing  10  and arranged to retain the balls  26  in their locking positions and to release the gear casing  15  by letting the balls  26  disengage at least one of the grooves. 
     The gear casing  15  comprises a two stage planetary type reduction gearing  18  and power transferring drive spindle  19 . The latter forms a square ended output shaft for connection to a nut socket. The first stage of the reduction gearing  18  comprises a sun gear  20  which is coupled to the motor via a connection shaft  21  and a non-illustrated angle drive. The gear casing  15  is one of a number of interchangeable gear casings, wherein the gear ratios of the gear casings are different. So, by changing gear casing it is possible to obtain a different gear ratio. However, the reduction gearing  18  per se is of a conventional type, and since it does not form any part of the invention it is not described in further detail. 
     The drive spindle  19  is provided with a torque sensing device  22  comprising an elastically deformable weak portion  23  of the drive spindle  19  and a strain gauge arrangement (not illustrated in further detail) fitted thereto. The drive spindle  19  is provided with a coaxial cavity  24 , and the weak portion  23  is formed by the circumferential wall of the cavity  24 . The cavity  24  could also be arranged non-coaxilly as long as the spindle with its components is balanced and has symmetrical properties to allow reliable signals from the strain gauges. Inside the cavity  24  there are located a number of electronic components forming a signal treating unit  25  connected to the strain gauge arrangement. 
     The signals produced by the torque sensing device  22  are transferred to an operation control unit for controlling the power wrench operation in relation to feed back signals received from the torque sensing device  22 . The control unit is not illustrated per se but is located either in the housing  10  or at a remote location separate from the wrench. In any case, the signals produced by the torque sensing device  22  have to be transferred to the housing  10 . The very first step to do this is to transfer the signals from the drive spindle  19  to the gear casing  15 . This is accomplished by a first contact free signal transferring device  28  which is connected to electric leads  29  in the gear casing  15 . This signal transferring device  28  is illustrated schematically only and may be of any known contact free type, for instance an induction device comprising magnets and coils, a device including a magnetostrictive material in the output spindle, a telemetric signal transferring device etc. 
     For transferring the torque sensor signals from the gear casing  15  to the housing  10  and to the control unit there is provided a second signal transferring device  31 , and an electric wiring  30  is provided in the housing  10  to connect the device  31  with the control unit, directly if located in the housing or via an external cable if located remotely from the wrench. The second signal transferring device  31  may be of a contact free type or a brush type. Since the rotation between the gear casing  15  relative to the housing  10  is relatively limited there will be no mechanical wear and that a brush type of signal transferring device will be safe and reliable enough. 
     In high power wrenches where a torque reaction bar is used to transfer the reaction forces to a suitable structure and to protect the operator from being exposed to these forces it is important that the gear casing on which the torque reaction bar is attached is rotatable or swivelled relative to the wrench housing and handle. This means that when an operation parameter sensing device, for instance a torque transducer, is provided on or close to the output shaft of the wrench there has to be a rotation admitting signal transferring device not only between the drive spindle/output shaft and the gear casing but also between the gear casing and the housing. In order to avoid mechanical wear and bad contact the signal transferring device between the drive spindle/output shaft and the gear casing has to be contact free. However, the signal transferring device provided between the gear casing and the housing is not exposed to such an extensive rotational movement, which means that the signal transferring device provided between these two parts may be of a simple brush type, as mentioned above. 
     The arrangement of a first and a second rotatable signal transferring devices makes it possible to locate an operation parameter sensing device on or close to the output shaft wherein the gear casing is rotatable and releasable relative to the wrench housing. It also means that the gear casing with an operation parameter sensing device which has been calibrated at its installation in relation to the actual application and a torque reaction bar fitted may be easily removable as a unit and exchanged for another gear casing unit with another gear ratio and/or torque reaction bar fitted. 
     In  FIG. 3  there is illustrated the front part of an angle type power wrench which comprises a housing  50  in which there is located a rotation motor and a planet type reduction gearing  58 . The front part of the power wrench comprises a gear casing  55  with an angle gear including a pinion  56  and a bevel gear  57 . The bevel gear  57  is formed integrally with a square ended output shaft  59  which is supported in bearings  61 ,  62 . The pinion  56  is formed integrally with a drive spindle  60  which is supported by bearings  63 ,  64 . At its rear end the drive spindle  60  is formed with a splined portion  65  for releasable drive connection with a planet wheel carrier  66  of the reduction gearing  58 . 
     A torque sensor comprising strain gauges  68  is attached to the drive spindle  60  so as to be activated by torsional elastic deformation of the drive spindle  60  during torque transfer. The drive spindle  60  comprises an internal co-axial cavity  71 , wherein a printed circuit board  73  is located. The cavity  71  could also be arranged non-coaxilly as long as the spindle with its components is balanced and has symmetrical properties to allow reliable signals from the strain gauges. The circuit board  73  carries electronic components  72  connected to the strain gauges  68  and arranged to treat the signals delivered by those. The circuit board  73  also comprises a memory unit for storing operation parameter data and/or the number of operation cycles performed by the gear casing. 
     The gear casing  55  is formed with a rear neck portion  75  to be received in a socket portion  76  of the housing  50 . The gear casing  55  is axially locked to the housing  50  by balls  77  and rotationally locked thereto by a splines connection  78 . The balls  77  are retained in their locking positions by a maneuver sleeve  79  movably supported on the housing  50 . The interface between the gear casing  55  and the housing  50  is illustrated by a line B-B. 
     The electric signals generated by the strain gauges  68  and treated by the electronic components  72  on the circuit board  73  are transferred to the housing  50  via a transferring device  84 . The latter comprises a stationary part  85  supported on the housing  50  and a rotating part  86  supported on a carrier element  87  secured to the rear portion  65  of the drive spindle  60 . In order to avoid mechanical wear and disturbances related thereto this signal transferring device  84  is of a contact free type, for instance inductive or telemetric. 
     In the housing  50  there is provided a non-illustrated wiring for connecting the second signal transferring device  84  with an operation control unit which is not illustrated per se but is located either in the housing  50  or at a remote location separate from the power wrench. 
     By providing a separate and releasable and/or exchangeable gear casing to the housing of a power wrench with at least one operation sensing means associated with the drive spindle and signal transferring devices between the drive spindle and the gear casing on one hand and between the gear casing and the power wrench housing on the other hand, as specified by the invention, provides the advantage of having a separate and exchangeable gear casing which is complete with calibrated operation sensing means which is automatically and simultaneously connected to an operation control unit as the gear casing is attached to the power wrench housing. This avoids sources of error and bad contacts and makes it possible to locate the operation sensing means after the reduction gearing, thereby avoiding to a large extent signal distortions.