Patent Publication Number: US-2022219249-A1

Title: Power drill and force transducer for such a drill

Description:
TECHNICAL FIELD 
     The present invention generally relates to power drills, more particularly to such drills comprising a force transducer for measuring a force exerted on the drill. 
     TECHNICAL BACKGROUND 
     Power drills for drilling in different materials are known to be used in various industries where, although requirements on the end result varies a lot, sometimes very high quality standards for the resulting holes are to be met. 
     Many factors influence the end result, i.e. the quality of the hole achieved for example in terms of entry roundness, entry concentricity, perpendicularity and conicality of the hole. Such factors include machining parameters where examples include drilling speed and feed rate and other factors such as drill bit wear. Further, depending on the material used, the axial force (i.e. the feed- or thrust force) may also have a significant influence on the end result achieved. 
     One common way of managing the feed force and hence at least to some degree the quality of the resulting hole, at least in the case of a hand held drill, is that the operator, based on skill and experience, simply applies what is considered an appropriate feed force. However, such methods are of course highly dependent on the skill and experience of the operator and therefore offer less repeatability. Further, no traceability is provided. Another issue is the lack of feedback provided to the operator, other than possible review after the drilling operation is finished which may reveal that the hole fails to fulfill the quality standards set. 
     In order to alleviate some of these problems, attempts have been made to use various types of force measuring devices, where examples include load cells, arranged in the drills. 
     However, there are many problems associated with such measurement devices remaining. For example related to measurement accuracy and further in that known devices tend to take up a lot of space and hence add to the size of the drill. 
     Hence, there exists a need for improvement in the field of force measurement in power drills. 
     SUMMARY OF THE INVENTION 
     Accordingly, it would be desirable to provide a design enabling improved measurements of the thrust force acting on the drill. In particular, it would be desirable to provide such functionality by means of a force transducer which does not require an unnecessary amount of space in the drill housing. To better address one or more of these concerns a power drill, a force transducer and a method as defined in the independent claims are provided. Preferred embodiments are defined in the dependent claims. 
     According to a first aspect of the invention a power drill is provided, the drill comprising a housing in which a motor is arranged and a front bearing and a rear bearing, the front and rear bearing being arranged at a front end of the housing to support an axle assembly drivingly connected to the motor at a first end and adapted at a second end to engage a drill attachment, wherein the axle assembly and at least one of the front bearing and the rear bearing further form an additional assembly movably arranged with respect to the housing such that an axial movement, in some cases a limited axial movement, between the housing and the additional assembly is allowed. The power drill further comprising a force transducer arranged at the front end of the housing, wherein the force transducer is axially supported by the housing and wherein the additional assembly is axially supported by the force transducer, the force transducer thereby being configured to sense a measured quantity and output a signal representing an axial force acting on the additional assembly. I.e. a force acting on or exerted by the drill, also referred to as the thrust force or feed force. 
     According to the first aspect, the power drill provides an inventive solution to the concerns described above by means of a design incorporating a force transducer and an axle assembly movably arranged with respect to this transducer which allows for accurate measurement of the axial force may to be obtained in an advantageously compact manner 
     More particularly, the axle assembly is supported by two bearing of which at least one likewise is movably arranged with respect to the transducer. The force transducer provided in the inventive power drill is configured to sense a measured quantity indicative of the axial force acting on the additional assembly and therefore measures the force in the feed direction of the drill via the axle assembly, i.e. the thrust force. Further, the additional assembly is axially supported by the transducer which in turn is axially supported by the housing. For example, in one embodiment, the force transducer may bear axially against the housing, in other embodiments an adapter or similar component may be arranged there between such that the additional assembly bears against the adapter which in turn bears against the housing. Similarly, in one embodiment, the additional assembly may bear axially against the force transducer, whereas in other embodiment an additional component such as an adapter or washer or the like may be arranged there between. 
     The drill attachment mentioned above could for example be a chuck or in some cases a modular drill head and the referenced power drill may for example be a hand held drill or a fixtured drill. Further, according to one embodiment, the power drill comprises circuitry for controlling the drill. For example, such circuitry may comprise a processor and a memory containing instructions executable by the processor, which when run in the power drill causes the drill to provide feedback to an operator based on the signal representing an axial force acting on the additional assembly and/or to store data during drilling. 
     According to one embodiment, the force transducer comprises a disc shaped portion coaxially arranged with respect to the front and rear bearing, wherein the measured quantity is a quantity measured over the disc shaped portion. I.e. a flat, thin and circular portion. Hereby, a particularly compact and space efficient design may be achieved. Mora particularly, a design adding virtually no extra axial length to the drill may be achieved using a disc shaped design, thereby solving a common problem of known transducers. 
     According to one embodiment, the force transducer is arranged behind the rear bearing, in a direction defined from said first end to said second end of said axle assembly, or in other words in a direction along the axle defined from the motor to the end adapted to engage a drill attachment, such that the rear bearing is supported by the force transducer. Behind in this sense hence being a position closer to the motor. In another embodiment, the transducer may be arranged in front of the front bearing in the direction defined above. 
     For example, the rear bearing may bear against the force transducer. In such an embodiment, the additional assembly may comprise the axle assembly and the rear bearing. Hereby, the force exerted by the rear bearing on the transducer may be measured by the transducer. Arranging the transducer behind the rear bearing may be advantageous in that the length of the wiring needed for the transducer is likely to be shorter, reducing noise in the signals. 
     In one embodiment, the measured quantity is a quantity indicative of the axial force acting on the additional assembly. According to one embodiment, the measured quantity is a quantity indicative of a strain, wherein the force transducer comprises at least one strain gauge. For example, several strain sensors may be arranged in a bridge configuration such as a Wheatstone bridge configuration. Other types of load cells are however conceivable within the scope of the present application. 
     According to one embodiment, the force transducer comprises a first end portion extending in the axial direction, a second end portion extending in the axial direction, and an intermediate portion extending in a radial direction between the first and second end portion, thereby forming the disc shaped portion. This transducer design is advantageous not only due to its space saving properties but also since this design provides for both positive and negative strain values on one side of the transducer body as an axial force is exerted on the transducer will result in tension as well as compression. Hereby, measurements of for example strain is significantly facilitated as they may be performed on only one side of the transducer with maintained accuracy. As the skilled person is well aware, a positive strain and a corresponding negative strain is commonly used to amplify the output when using strain gauges, for example gauges arranged in a bridge configuration. By the term side should in this case, and throughout the present specification, be understood the opposite sides of the intermediate portion which are normal to the axle as the transducer is arranged in the drill. I.e., what may commonly be referred to as a front and back side of the disc shaped portion and hence of the transducer. 
     According to one embodiment, the first end portion is axially supported against the housing, and the additional assembly is supported against the second end portion. Hereby, the deformation and hence the strain mentioned above arise as the rear bearing, the assembly and optionally the front bearing is displaced towards the portion of the housing against which the first end portion of the transducer bears as a thrust force acts on the drill. More particularly, a tension will arise in a region closer to the second portion whereas a compression will arise in a region closer to the first portion, on the side of the transducer facing away from the additional assembly. In one embodiment, the first end portion bears axially against the housing. In another embodiment, the first end portion bears against an adapter or similar component which in turn bears against the housing. For example, in one embodiment, the rear bearing bears against the second portion. 
     According to one embodiment, the force transducer comprises at least two strain gauges, respectively arranged on a first and a second side of the disc shaped portion. E.g. on a respective annular face of the respective first and second side. For example, in some embodiments, the force transducer instead may be described as a substantially disc shaped washer, i.e. the disc shaped portion mentioned above in such an embodiment constitutes most of or even the whole transducer. Hereby, the transducer adds even less axial length to the drill. In such an embodiment, strain sensors may be arranged on both sides of the washer. 
     According to one embodiment, the force transducer is arranged behind the front bearing in a direction defined from said first end to said second end of said axle assembly, such that the front bearing is supported against the force transducer, such that the rear bearing is supported by the force transducer. Again, in other words in a direction along the axle defined from the motor to the end adapted to engage a drill attachment, and behind in this sense hence being a position closer to the motor. For example, the front bearing may bear against the force transducer. In such an embodiment, the additional assembly may comprise the axle assembly and the front bearing. Hereby, the force exerted by the front bearing on the transducer may be measured by the transducer. Arranging the transducer behind the front bearing may be advantageous in that the distance to the windings of the motor is increased, which may reduce noise in the signal due to lower electromagnetic interference from the motor. Further, an amplifier may be arranged closer to the transducer. Further advantages are related to the fact that the size of the front bearing, and hence the ability of the bearing to withstand reaction forces, may more easily be increased. 
     Accordingly, in one embodiment, the force transducer comprises at least one strain gauge arranged on a first side of the disc shaped portion. More particularly, on an annular face of this first side. For example, in one embodiment, a diaphragm strain gauge is arranged on one side of the disc shaped portion. A diaphragm strain gauge, also known as a membrane strain gauge, commonly comprising strain gauges arranged in a rosette or bridge configuration may be designed to fit the disc shaped portion of the force transducer. 
     According to one embodiment, the power drill further comprises a motor shaft connected to the motor at a first end and forming a sun gear at a second end, wherein the axle assembly comprises a planet carrier adapted to engage the drill attachment and at least one planet gear adapted to engage a ring gear arranged between the front bearing and the rear bearing, the motor shaft and planet carrier being coupled, or connected, via the ring gear and the at least one planetary gear. In one embodiment, the ring gear may be comprised by the axle assembly. 
     According to one embodiment, the axle assembly, the front bearing and the rear bearing together form the additional assembly movably arranged with respect to the housing. 
     According to a second aspect of the present invention, a force transducer for a power drill according to any of the embodiments described in the foregoing is provided. 
     According to a third aspect of the present invention, a method in a power drill according to any of the embodiments described in the foregoing for providing feedback to an operator is provided, wherein the feedback is a feedback based on the signal representing an axial force acting on the additional assembly. Hereby, quality of the finished hole may be improved. According to one embodiment, the feedback is a feedback provided during drilling, such that an operator exerting too much or too little force is alerted and given the opportunity to correct the force level applied already during drilling. Such feedback may be provided by means of visual, audible or haptic feedback to the operator. According to one embodiment, the feedback is a feedback provided after the drilling of a hole is finished. Hereby, the quality of the finished hole may be evaluated and the hole may be given an approved or not approved status. In one embodiment, the method further comprises the step of detecting drill bit wear by analysis of the data provided by the force sensor. 
     According to a fourth aspect of the invention a detachable front part for a power drill is provided, the drill comprising a housing in which a motor is arranged, the detachable front part comprising a front part housing adapted to be attached to the power drill housing and a front bearing and a rear bearing, the front and rear bearing being arranged in the front part housing to support an axle assembly adapted to be drivingly connected to the motor at a first end and adapted at a second end to engage a drill attachment, wherein the axle assembly and at least one of the front bearing and the rear bearing further form an additional assembly movably arranged with respect to the front part housing such that an axial movement, e.g. a limited axial movement, between the front part housing and the additional assembly is allowed. The front part further comprising a force transducer, wherein the force transducer is axially supported by the front part housing and wherein the additional assembly is axially supported by the force transducer, the force transducer thereby being configured to sense a measured quantity and output a signal representing an axial force acting on the additional assembly. In one embodiment, the front part further comprises circuitry, .e.g. wiring, for signal transferring between the front part and the power drill and/or between the front part and a controller. Such signals may include the signal output from the force transducer. 
     Objectives, advantages and features conceivable within the scope of the second, third and fourth aspect of the invention are readily understood by the foregoing discussion referring to the first aspect of the invention. 
     Further objectives of, features of and advantages of the present invention will become apparent when studying the following detailed disclosure, the drawings and the appended claims. Those skilled in the art realize that different features of the present invention can be combined to create embodiments other than those described in the following. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The invention will be described in the following illustrative and non-limiting detailed description of exemplary embodiments, with reference to the appended drawing, on which 
         FIG. 1  is a cross sectional view of a front end of an exemplary power drill according to one embodiment. 
         FIG. 2  is a cross sectional view of a front end of an exemplary power drill according to a second embodiment. 
         FIG. 3  is a perspective view of an exemplary force transducer according to one embodiment. 
         FIG. 4  is a perspective view of an exemplary force transducer according to one embodiment. 
     
    
    
     All figures are schematic, not necessarily to scale and generally only show parts which are necessary in order to elucidate the invention, wherein other parts may be omitted or merely suggested. 
     DETAILED DESCRIPTION 
     A front end of an exemplary power drill  1 , more particularly a handheld power drill, is shown in cross sectional view in  FIG. 1 a   , the drill comprising a housing  10  in which a motor (not shown) is arranged at a left side of  FIG. 1 . A motor shaft  6   a  is connected to the motor at a first end and forms a sun gear  60  at a second end  6   b . A front bearing  3  and a rear bearing  2  are arranged at a front end  10  of the housing  10  to support an axle assembly  20  and a spring  3   a  is arranged to bias the bearings. The axle assembly is drivingly connected to the motor at a first end  20   a  and adapted at a second end  20   b  to engage a drill attachment DA, in the illustrated embodiment a drill chuck. More particularly, the axle assembly  20  comprises a planet carrier  70  adapted to engage the drill chuck and a number of planet gears connecting the motor shaft  6  (i.e. the sun gear formed thereby and the planet carrier  70  via a ring gear  50  arranged between the front bearing  3  and the rear bearing  2 . The skilled person realizes that the front end shown in  FIG. 1  may also form a detachable front part of a power drill  1 . 
     The axle assembly  20  and, in the illustrated embodiment, the front bearing  3  and the rear bearing  2  together form an additional assembly which is movably arranged with respect to the housing  10 . Hereby, a limited axial movement between the housing  10  and the additional assembly is allowed. 
     A force transducer  30  is also arranged at, i.e. close to, the front end  10   a  of the housing  10 . More particularly, the force transducer is axially supported by the housing, in the illustrated embodiment the transducer bears against an adapter  35  which in turn bears against the housing. Further, the additional assembly mentioned above in turn bears axially against the force transducer  30 , in this case via the rear bearing  2 . Hence, when drilling is performed, the thrust force on the additional assembly may be measured by the transducer portion against which the assembly bears since the force transducer is configured to sense the resulting strains and output a signal representing this axial force acting on the assembly. The force being due to the limited displacement of the additional assembly with respect to the housing  10  mentioned above. 
     The force transducer  30  in the illustrated embodiment is arranged behind the rear bearing  2 , that is to say behind in a direction D defined along the axle  6  from the first end  20   a  to the second end  20   b , i.e. also from the first end  20   a  to the second end  20   b  of the axle assembly  20 , such that the rear bearing  2  bears against the force transducer  30 . More particularly, the force transducer  30  of the exemplary embodiment, shown in greater detail in  FIG. 3 , further comprises a first end portion  32  extending in the direction D and bearing against in this case the adapter  32  and a second end portion  33  extending in the direction D against which the rear bearing  2  bears. An intermediate portion  31  extends in a radial direction between the first and second end portion and forms a disc shaped portion  31  which is coaxially arranged with respect to the rear bearing  3  (and hence to the axle  6  and the front bearing  2  as well). As may be seen in greater detail in  FIG. 3 , the diaphragm strain gauge  80  is arranged on the side facing away from the rear bearing  2 . 
     A force transducer  30  suitable for the embodiment of the drill in  FIG. 1  is shown in  FIG. 3 . This force transducer measures the strain in the disc shaped portion  31 , i.e. the measured quantity is a strain resulting from the relative displacement between the additional assembly and the housing due to the thrust force. To provide these values, the transducer comprises strain gauges. More particularly, a so called diaphragm or membrane strain gauge  80  is arranged on one side  31   a  of the disc shaped portion  31 , i.e. on the annular face or surface  31   a  visible in  FIG. 3 . This circular, or annular, diaphragm is adapted to the shape of the disc shaped portion  31  and comprises a plurality of strain gauges arranged to measure the resulting strain in the disc shaped portion  31  of the force transducer  30 . 
     Turning to  FIG. 2 , a front end of an exemplary power drill  1 ′, also in this case a handheld power drill, is shown in cross sectional view. The arrangement of the housing, bearings and front, axle assembly and front- and rear bearing is substantially the same as for the embodiment shown in  FIG. 1  and will therefore not be described again. 
     Also as in the embodiment of  FIG. 1 , a force transducer  30 ′ is arranged at, i.e. close to, the front end  10   a  of the housing  10 ′. More particularly, the force transducer is axially supported by the housing, in the illustrated embodiments the transducer bears against a washer  90  which in turn bears against the housing. Further, the additional assembly mentioned above in turn bears axially against the force transducer  30 ′, in this case via the front bearing  3 ′. Hence, when drilling is performed, the thrust force on the additional assembly may be measured by the transducer portion against which the assembly bears since the force transducer is configured to sense the resulting strains and output a signal representing this axial force acting on the assembly. The force being due to the limited displacement of the additional assembly with respect to the housing mentioned above. 
     The force transducer  30 ′ in the embodiment of  FIG. 2 , unlike the embodiment of  FIG. 1 , is however arranged behind the front bearing  3 ′, that is to say behind in the direction D defined above, such that the front bearing  3 ′ bears against the force transducer  30 ′. 
     Further, turning to  FIG. 4  showing one example of a force transducer  30 ′ suitable to be arranged in the drill shown in  FIG. 2 , this exemplary embodiment may be described as a substantially disc shaped washer  30 ′ which is adapted to be coaxially arranged with respect to the front bearing (and hence to the axle and rear bearing as well). I.e. the disc shaped portion  31 ′ constitutes most of the transducer  30 ′. 
     In order to measure the strain in the disc shaped portion  31 ′, the force transducer in  FIG. 4  comprises a number of strain gauges  80 ′, respectively arranged on a first side  31   a ′ and a second opposite side (not visible in  FIG. 4 ) of the disc shaped portion  31 ′. In the illustrated embodiment, eight strain gauges are arranged on the first side of the transducer  30 ′, i.e. on the front and back side of the washer  30 ′. 
     Hereby, an accurate measurement of the thrust force may be achieved. Further, as an additional advantage as the thrust force is measured during the drilling, feedback may be provided to the operator during drilling and hence the quality of the resulting hole may be significantly improved. Needless to say, data may also be stored and used for analysis after the drilling is performed as well. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiment. The skilled person understands that many modifications, variations and alterations are conceivable within the scope as defined in the appended claims. For example, the power drill may be a fixtured drill. Further, any one of the disclosed exemplary embodiments of the force transducer may be arranged in any of the disclosed exemplary embodiments of the power drill. 
     Additionally, variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, form a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope of the claims.