Abstract:
An electric hand power tool includes a cylindrical device section, a control element displaceable about the cylindrical device section, and an electric scanning device disposed at the device section and configured to determine a rotary position of the control element. The scanning device is configured to optically scan the rotary position.

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP 2011/051522, filed on Feb. 3, 2011, which claims the benefit of priority to Serial No. DE 10 2010 001 967.4, filed on Feb. 16, 2010 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     Electric hand power tools often comprise an electric drive motor which causes a tool or tool holder to rotate by means of a transmission. An energy supply for the electric hand power tool can be provided using an energy store connected to the hand power tool, for example a battery or rechargeable battery, or by an electric supply network, for instance, via an electric supply line. 
     In order to be able to make the electric hand power tool as compact as possible, control elements are preferably designed in such a manner that they only slightly change an outer contour of the electric hand power tool. This ensures accessibility of the electric hand power tool to workpieces, even under restricted spatial conditions. 
     For this purpose, a control element which can be moved substantially around the drive train in a rotating or pivoting movement is occasionally provided in the region of the often cylindrical drive train. Such a control element is usually electrically scanned using a sliding contact which is fastened to the control element and opens or closes contacts of a scanning printed circuit board according to a rotary position of the control element. The scanning printed circuit board extends substantially in a plane perpendicular to the axis of rotation of the control element and is limited in the radial direction, on the inside and outside, by a circle line. 
     Production and mounting of the scanning printed circuit board are complicated, which may increase production costs of the electric device. Furthermore, the contacts and the sliding contact are exposed to moisture and dirt which may arise in the region of the electric hand power tool. 
     The disclosure is based on the object of specifying an electric hand power tool having an improved scanning apparatus. 
     SUMMARY 
     The disclosure solves this problem with an electric hand power tool having the features of the disclosure. 
     An electric hand power tool comprises a cylindrical device section, a control element which is movable around the cylindrical device section, and an electric scanning apparatus which is arranged on the device section and is intended to determine a rotary position of the control element, the scanning apparatus being set up to optically scan the rotary position. 
     Disturbing influences caused by moisture, dust and vibrations, which may be present in the region of the hand power tool, are advantageously effectively suppressed by the optical scanning. 
     The scanning apparatus may comprise a plurality of binary scanning elements, each of which provides a binary digit of a binary coded representation of the rotary position. This makes it possible to directly determine an absolute rotary position with high resolution by means of a minimum number of scanning elements. The rotary position determined in this manner can be advantageously digitally processed further without further conversion, for example by means of an integrated digital controller. 
     In this case, the rotary position may be coded in such a manner that the binary representations of respective adjacent rotary positions of the control element differ in at most one binary digit. In contrast to a conventional dual code or BNC code, such highly differing incorrect measurements, which may arise if a plurality of binary digits change between two adjacent rotary positions, are avoided, but this takes place only with a certain angular offset, for example on account of imperfections in the structure of the control element with the scanning elements. If a measurement takes place within the angular offset, an incorrect measurement can be carried out with an error which may amount to the most significant binary digit, which may correspond to half the range of values of the scanning apparatus. As a result of the coding according to the disclosure, an incorrect measurement may amount, at most, to the value of the difference between adjacent rotary positions, which usually corresponds to the least significant binary digit. 
     The control element may have a number of position markings in the shape of a circular arc, each scanning element being set up to scan a position marking assigned to it, and at least two position markings being on the same circumference around the axis of rotation of the control element. This advantageously makes it possible to increase a resolution of the coded rotary position of the control element without using additional installation space or makes it possible to reduce a mechanical extent of the control element with the same resolution. 
     For this purpose, a coding disk which extends in the radial direction with respect to the axis of rotation of the control element may be connected to the control element. The position markings may be in the form of apertures or reflective marks in/on the coding disk. The scanning elements may comprise light barriers or reflection light barriers. It is possible to use visible or invisible light, for example infrared light, and the light may be modulated in order to suppress interference caused by extraneous light. The reflective marks may be arranged on different sides of the coding disk. This advantageously makes it possible to save further installation space in the radial direction of the coding disk, with the result that the electric hand power tool can be even more compact. 
     The electric hand power tool may comprise a controller which is designed to control an electric drive device of the hand power tool on the basis of the rotary position of the control element. This advantageously makes it possible for a user of the hand power tool to control, in particular, a rotational speed of the drive device and/or a torque of the drive device in an intuitive manner. The controller may be arranged, together with the scanning elements, on a common flat printed circuit board. This makes it possible to avoid connecting special components, thus making it possible to reduce production costs for the electric hand power tool. 
     The cylindrical device section may comprise an electric motor and/or a planetary transmission of the hand power tool. The control element and possibly the controller may be integrated with the electric motor and/or the planetary transmission, thus forming a universal drive assembly which can be used in a multiplicity of different electric hand power tools. 
     The control element may be movable around an axis of rotation which extends parallel to a longitudinal axis of the cylindrical device section. In this case, the axis of rotation may coincide with the longitudinal axis or may run with an offset with respect to the latter. The movability of the control element may thus be adapted to a contour of a housing which surrounds the cylindrical device section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure is now described in more detail with reference to the accompanying figures, in which: 
         FIG. 1  shows a schematic illustration of a cordless screwdriver; 
         FIG. 2  shows an isometric view of the drive device of the cordless screwdriver from  FIG. 1 ; 
         FIG. 3  shows a plan view of the coding disk from  FIG. 2 ; and 
         FIG. 4  shows an assignment table between rotary positions and states of the scanning apparatuses from  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a schematic illustration of a cordless screwdriver  100 . The cordless screwdriver  100  illustrated is representative of any desired electric hand power tool; other embodiments may also include, for example, a drill, a lighting device or a measuring instrument having a cylindrical device section with a corresponding control element. The cordless screwdriver  100  comprises an electric drive motor  105 , a planetary transmission  110 , an electronic controller  115 , a control element  120  and a rechargeable battery  125 , which are arranged in a housing  130  of the cordless screwdriver  100 . In addition, a tripping device  135  and a drill chuck  140  on the cordless screwdriver  100  are accessible from the outside. 
     Depending on a position of the control element  120  and of the tripping device  135 , the electronic controller  115  provides a flow of electrical energy from the rechargeable battery  125  to the electric drive motor  105 . The torque output by the electric drive motor  105  is transmitted to the planetary transmission  110  and from there to the drill chuck  140 . The drill chuck  140  is set up to receive a tool, for example a drill or a milling cutter to which the rotation of the drill chuck  140  is transmitted. The electric drive motor  105  and the planetary transmission  110  form the drive device  145 . 
     In other embodiments of the cordless screwdriver  100 , the rechargeable battery  125  is at a different position, with the result that the housing  130  has as compact and ergonomic a shape as possible, for example substantially rotationally elliptical or cylindrical. 
       FIG. 2  shows an isometric view of the drive device  145  of the cordless screwdriver  100  from  FIG. 1 . The electric drive motor  105  and the planetary transmission  110  extend along a common axis of rotation  250 . The electronic controller  115  is arranged on a printed circuit board  220 , the printed circuit board  220  carrying light barrier elements  205 . The light barrier elements  205  scan a coding disk  230  which is arranged coaxially with respect to the electric drive motor  105  and the planetary transmission  110  in a manner rotatable around the axis of rotation  250 . The coding disk  230  extends substantially in a direction radial to the axis of rotation  250  and comprises a driver  240  which runs parallel to the axis of rotation  250  and is intended to engage with the control element  120  from  FIG. 1 . 
     A further light barrier element  205  is arranged opposite each of the light barrier elements  205  on the respective opposite side of the coding disk  230 . Two light barrier elements  205  in each case form a light barrier  210  which scans the coding disk  230  at a predetermined radial distance from the axis of rotation  250 . 
     In the embodiment illustrated, the coding disk  230  has recesses which allow or do not allow light to pass between light barrier elements  205  of a light barrier  210  depending on the rotary position of the coding disk  230 . In another embodiment, the coding disk  230  may also have reflective marks instead of recesses, and the light barriers  210  may each be completely on one of the sides of the coding disk  230  in order to scan the reflective marks. 
     The coding disk  230  is mounted and guided in grooves in the housing  130  from  FIG. 1 . The driver  240  engages in the control element  120  from  FIG. 1  in such a manner that a pivoting movement of the control element  120  around the axis of rotation  250  is transmitted to the coding disk  230 . 
       FIG. 3  shows a plan view of the coding disk  230  from  FIG. 2  along the axis of rotation  250 . The coding disk  230  has a number of recesses  305  which run on circular paths with different radii r 1  and r 2  around the axis of rotation  250 . Along the circular paths around the radii r 1  and r 2 , the recesses  305  are arranged in such a manner that they allow or do not allow light from the light barrier elements  205  to pass depending on the rotary position of the coding disk  230  with respect to the printed circuit board  220  from  FIG. 2 . The coding disk extends at an angle of approximately 180° around the axis of rotation  250 . The maximum angle of rotation of the coding disk  230  from  FIG. 3  is below 90°, with the result that an outer left-hand track  310 , an inner left-hand track  320 , an outer right-hand track  330  and an inner right-hand track  340  result with respect to the driver  240 , which tracks are each scanned by different light barriers  210  from  FIG. 2 . 
     In a further embodiment, reflective markings may also be applied along the tracks  310  to  340  instead of recesses  305 , and the light barriers  210  constructed from the light barrier elements  205  may be reflection light barriers. Mutually corresponding light barrier elements  205  are then always on the same side of the coding disk  230 . Different tracks corresponding to the tracks  310  to  325  may be opposite one another on the front side and rear side of the coding disk  230 . The coding disk  230  may be scanned from each side using, for example, four light barriers each comprising two light barrier elements  205 , which increases a resolution of the determined rotary position by a factor of 2 4 =16. Alternatively, four tracks analogous to the tracks  310  to  325  may be scanned, for example, using two reflection light barriers on each side of the coding disk  230 , all four tracks having the same radius with respect to the axis of rotation of the coding disk  230 . 
       FIG. 4  shows an assignment table  400  between rotary positions of the coding disk  230  and states of the light barrier elements  205  or light barriers  210  from  FIG. 2 . 16 rotary positions of the coding disk  230  from  FIGS. 2 and 3  and of the control element  120  from  FIG. 1  are provided in a horizontal direction. One row is indicated for each light barrier  210  from  FIG. 2  in the vertical direction. In the assignment table  400 , a white field represents an interrupted flow of light between the corresponding light barrier elements  205  and a black field represents an existing flow of light. The flow of light may be enabled by a recess  305  in the coding disk  230  according to  FIG. 3  or, in the case of a reflection light barrier, by a reflective region on the coding disk  230 . 
     The uppermost row illustrated in  FIG. 4  corresponds to the least significant binary digit (Least Significant Bits, LSB) of the illustrated code; the significance of the illustrated binary digits increases in the downward direction to the most significant binary digit (Most Significant Bit, MSB) in the fourth row. 
     The illustrated coding between rotary positions and binary states of the four different light barriers  210  corresponds to a four-bit Gray code. This code is distinguished by the fact that only the state of a single binary digit (bit) changes in each case between adjacent values or rotary positions. In contrast to the conventional dual coding, this dispenses with the need to position the light barrier elements  205  exactly with respect to the coding disk  230  in such a manner that the states of a plurality of light barriers  210  change with respect to the absolutely identical rotary position between adjacent rotary positions of the coding disk  230 , which is associated with great practical difficulties. 
     If the light barriers  210  do not switch at the same angular position when the dual code is used, a result may be read between these two angular positions, which result is corrupted by a value dependent on the sum of the significances of the binary digits to which the switching light barriers  210  are assigned. In the worst case scenario, the error may reach a value of the most significant binary digit, which may amount to half of the range of values of the coding or half the rotary position range, that is to say eight positions. In the case of the Gray coding illustrated in the assignment table  400 , only a maximum of one error may arise between adjacent rotary positions of the coding disk  230  as a result of incorrect scanning, which error corresponds to a rotary position. 
     For further processing of the determined rotary position of the coding disk  230 , the Gray code illustrated in  FIG. 4  may be converted into a dual code, for example, in a known manner. Conversion is clear and generally known in both directions.