Patent Publication Number: US-2017361432-A1

Title: Power tool with telescopic output shaft

Description:
The invention relates to a torque delivering power tool with a telescopically arranged output shaft. Specifically, the invention relates to such a tool with an improved functionality with respect to the interaction with a work piece. The invention is especially adapted to torque wrenches, i.e. power tools adapted to tighten and loosen screw joints. 
     BACKGROUND 
     An operator holding a hand held torque delivering power tool should provide a moderate axial force to the power tool, such that the tool implement of the output shaft will stay in positive contact with the work piece and apply a positive force to the operation. Generally, if the tool implement is a drill bit the axial force needs to be relatively great in order to push the drill bit through the material. 
     If, on the other hand, the tool implement is a screw bit, the axial force should be sufficiently great so as to guarantee a good connection between the tool implement and the work piece, e.g. a bolt or screw, but at the same time it should not be so hard that the workpiece risks getting damaged. 
     For fixed tools it is also important to provide an axial force that is within an acceptable range. For fixed tools the axial force needs to be automatically adjusted throughout a torque delivering operation, whereas it will have to be manually supervised for a handheld tool. 
     The invention is based on the notion that there is a need of an arrangement for a power tool by means of which it is possible to control the axial force by which the output shaft acts on a work piece, while still allowing a certain flexibility concerning the axial position of the power tool. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a torque delivering power tool by means of which it is possible to control the axial pressure at which the output shaft acts on the work piece. 
     This object is achieved by the invention according to claim  1 , which relates to a torque delivering power tool with a telescopically arranged output shaft including:
         a motor,   a housing,   an input shaft, which is driven by said motor,   an output shaft, which is rotationally connected to the input shaft and axially translatable with respect to the input shaft. A sensor is arranged to monitor an axial position of the output shaft with respect to the input shaft.       

     By monitoring the axial compression force acting between the output shaft and the input shaft it will be possible to control the axial force so as to continuously apply an axial compression force that is within a desired range. 
     In a specific embodiment of the invention the output shaft is telescopically arranged with respect to the input shaft between a fully extended position and a fully compressed position, wherein a resilient member having a known resilience in function of the extension is arranged to urge the output shaft towards the fully extended position, such that the extension of the output shaft continuously reflects the compression force acting between the output shaft and the input shaft. 
     With this specific embodiment it will be possible to uphold flexibility in the axial positioning of the tool, and still provide a axial force within a specific desired range. 
     Other features and advantages of the invention will be apparent from the figures and from the detailed description of the shown embodiment, and from the dependent claims. 
    
    
     
       SHORT DESCRIPTION OF THE DRAWINGS 
       In the following detailed description reference is made to the accompanying drawings, of which: 
         FIG. 1  is a perspective view of a torque delivering power tool according to a specific embodiment of the invention with a telescopically arranged output shaft shown in a fully extended position; 
         FIG. 2  is a sectional view of a front part of the power tool shown in a fully extended position; 
         FIG. 3  is a perspective view of the torque delivering power tool shown in  FIG. 1  with the telescopically arranged output shaft shown in a fully compressed position; and 
         FIG. 4  is a sectional view of a front part of the power tool shown in in a fully compressed position. 
     
    
    
     DETAILED DESCRIPTION OF THE SHOWN EMBODIMENT OF THE INVENTION 
     In  FIG. 1  a torque delivering power tool  10  according to a specific embodiment of the invention is shown. In the shown embodiment the power tool is a power wrench adapted to tighten and loosen screw joints. This is a preferred embodiment of the invention. 
     The power tool  10  comprises a housing that comprises several parts, including a front housing part  11 , a rear housing part  13 , and between these two parts a frame housing part  14  with a hollow mid portion that is covered by a casing  15 . The casing  15  may be removed to grant access to electronics housed inside the space enclosed by the casing  15  and the frame housing part  14 . 
     A motor (not shown) is arranged in the rear housing part  13  and a gear portion may be arranged inside the upper part of the frame housing part  14  and casing  15 . An output shaft  17 , drivingly connected to the motor is partly housed inside the front housing part  11  and extends out from the same. In  FIG. 1  the output shaft  17  is in a fully extended position P E . 
     At a rear side of the frame housing part  14  a connection port  18  is arranged. The bottom of the housing part  14  includes a fixation element (not shown) for fixing the power tool  10  to a robot arm or the like. The shown embodiment of the power tool is an electric torque wrench and hence the connection port  18  includes connection pins for electric power and signalling. An indication unit  19 , in the form of a light source, is arranged at a rear end of the rear housing part  13  in a position where it is clearly visible to the operator. 
     A front part of the power tool is shown in detail in a sectional view in  FIG. 2 . As is apparent from this view the power tool further comprises an input shaft  16 . The input shaft  16  is driven by the motor (not shown) via motor gear  26 . The motor gear  26  may be an integral part of a motor shaft is preferable driven by the motor via at least one reduction gear such as a planetary gear. Hence, preferably, the motor gear  26  is an output end of a reduction gearing. The output shaft  17  is rotationally connected to the input shaft  16  via a splined connection  23  and is journalled in bearings  25  with respect to an inner housing part  12 . The bearings  25  includes a splined inside that allows the output shaft  17  to translate axially with respect to the bearings  25  and the inner housing  12 . 
     A sensor  20  is arranged to monitor an axial compression force acting between the output shaft  17  and the input shaft  16 . In the shown embodiment the sensor  20  monitors the axial position of the output shaft  17  with respect to the input shaft  16 . A movement indicator  27  such as a magnet ring is located around an inner part of the output shaft  17 . The sensor  20  is arranged to monitor the movement of the movement indicator  27  so as to deduce the axial position of the output shaft  17 , and hence it&#39;s axial extension with respect to the housing  11 . The sensor  20  may be a hall sensor, an inductive sensor, or a capacitive sensor indicating the axial extension between the output shaft  17  and the input shaft  16 . The movement indicator  27  is adapted to the type of sensor used in a manner known in the art. 
     The output shaft  17  is telescopically arranged with respect to the input shaft  16  to allow axial movement of the output shaft  17  with respect to the input shaft  16  between a fully extended position P E  (shown in  FIGS. 1 and 2 ) that corresponds to a minimum compression force and a fully compressed position P C  (shown in  FIGS. 3 and 4 ) that corresponds to a maximum compression force. 
     A resilient member  21 , e.g. in the form of a torsional spring and having a known resilience in function of its extension, is arranged to urge the output shaft  17  towards the fully extended position P E , such that the extension of the output shaft  17  continuously reflects the compression force acting between the output shaft  17  and the input shaft  16 . Thereby, it is possible to deduce the axial compression force acting between the output shaft  17  and the input shaft  16  from the axial position of the output shaft  17 . 
     The indication unit  19  may be arranged to indicate the axial compression force acting between the output shaft  17  and the input shaft  16  based on the level of extension between the shafts. As an example the indication unit may emit a red light when the axial force is outside an allowable range. Further, to differentiate a too high axial pressure from a too low axial pressure, different colours may be dedicated to different states or rapid blinking light may be dedicated to the too high torque level, and slow blinking or a continuous light may be dedicated to the too low torque level. Also, the indication means may indicate a range inside which the level of extension between the shafts  16 , 17  corresponds to an acceptable compression force acting between the output shaft  17  and the input shaft  16 . For example, a white light may be produced for as long as the axial force is inside the acceptable range, and at a the end of a successful tightening operation the light may switch to a green light. 
     The indication unit may also include a sound indicator that produces a typical sound such as a high frequency beat when the axial force is higher than the allowed axial force. Further, the indication unit may be located distant from the actual power tool, e.g. integrated in a control panel used for controlling the tool. In such a control panel data of different kinds may be selectively shown and stored in order to control tightening operations. 
     The torque delivering power tool  10  may comprise a control unit, which either may be located in the tool itself or in the control panel. The sensor  20  may be arranged to continuously during operation transmit the monitored axial compression force acting between the output shaft  17  and the input shaft  16  to the control unit, the control unit being adapted to deliver a signal to the indication unit  19  in order to indicate the axial compression force acting between the output shaft  17  and the input shaft  16 . 
     The control unit is adapted to alert an operator of the tool, e.g. via the indication unit  19 , if the axial force exceeds a predetermined upper threshold or if it reaches below a predetermined lower threshold. 
     The power tool  10  may further be configured to start a specific operation only when the level of extension of the output shaft  17  with respect to the input shaft  16  is within a predetermined range. An operation may also be interrupted if the axial force reaches below or above a certain threshold. 
     Above, the invention has been described with reference to a specific embodiment. The invention is however not limited to this embodiment. 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.