Patent Publication Number: US-2021185909-A1

Title: Trimmer Head with Residual Trimmer Line Indicator

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a trimmer head for mounting on a drive shaft of a trimmer. 
     A trimmer serves for mowing grass, shrub or the like. For this purpose, a trimmer head with a tool is driven in rotation about an axis of rotation of the trimmer head so that the grass is cut off upon contact with the tool. As a tool, trimmer lines are used which are subject to a certain wear in operation of the trimmer head. During operation of a trimmer head, the trimmer line must be readjusted several times so that a sufficient length of trimmer line is available and the cutting function of the trimmer head is not impaired. When the trimmer line is completely unwound from the trimmer line spool, a new trimmer line must be inserted into the trimmer head. 
     It is advantageous when the operator is enabled to anticipate an upcoming change of the trimmer line. This enables the operator to keep at hand a replacement trimmer line and to change at the site of use the trimmer line, as needed. The operator, in preparation before even beginning work, can change the trimmer line so that an interruption of the work on site is not necessary. 
     WO 2018/153424 A1 discloses a trimmer head with a trimmer line wherein the trimmer line comprises sections of different color. Based on the differently colored sections of the trimmer line, the user can recognize how much trimmer line is already used up and when to expect a necessary exchange of the trimmer line. A disadvantage of such systems is that the recognition of the residual trimmer line length is possible only as a function of the trimmer line type. 
     It is an object of the invention to develop a trimmer head with an alternative residual trimmer line indicator. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, this is achieved by a trimmer head for mounting on a drive shaft of a trimmer, wherein the trimmer head comprises a housing and a trimmer line spool for winding and unwinding a trimmer line, wherein the trimmer line spool is rotatably supported in relation to the housing about an axis of rotation, wherein the trimmer line spool comprises, in relation to the housing, a first rotational direction and a second rotational direction opposite to the first rotational direction, wherein the trimmer head comprises a counting device for detecting the residual trimmer line length, wherein the counting device is operatively connected to the trimmer line spool such that the counting device is counting up upon rotation of the trimmer line spool in the first rotational direction in relation to the housing and is counting down upon rotation of the trimmer line spool in the second rotational direction in relation to the housing. 
     The trimmer head according to the invention comprises a trimmer line spool for winding and unwinding a trimmer line. The trimmer line spool comprises, in relation to the housing, a first rotational direction and a second rotational direction opposite to the first rotational direction. The trimmer head comprises a counting device for detecting the residual trimmer line length. The counting device is operatively connected to the trimmer line spool in such a way that the counting device counts up upon rotation of the trimmer line spool in the first rotational direction in relation to the housing and counts down upon rotation of the trimmer line spool in the second rotational direction in relation to the housing. 
     When the trimmer line is wound onto the trimmer line spool, the counting device counts up. When the trimmer line is unwound from the trimmer line spool, the trimmer line spool rotates in the second rotational direction in relation to the housing and the counting device counts down. In this context, the counter value is indicated by the counting device at least indirectly. In this way, the operator is advised by the counting device how much residual trimmer line length is still remaining on the trimmer line spool. The determination of the residual trimmer line length is realized independent of the configuration of the trimmer line. 
     Preferably, the counting device comprises a counter wherein the counter determines the relative rotation between trimmer line spool and housing. Advantageously, the counter is a mechanical, an electronic, or an electromechanical counter. By means of the counter, the relative rotations between trimmer line spool and housing can be measured by which the trimmer line is wound onto the trimmer line spool. 
     It is advantageously provided that at the trimmer line spool of the trimmer head at least one actuating element is provided wherein the counter is actuated at least once by means of the at least one actuating element for each relative rotation between the trimmer line spool and the housing. In this way, the counter counts the numerical value up or down by 1 for each revolution. Advantageously, a plurality of actuating elements can be provided also wherein the counter for each revolution determines a counter value which corresponds to the number of actuating elements. 
     The actuating element is preferably a tooth element which is arranged at the trimmer line spool. It is advantageously provided that the actuating element is a ring gear which is arranged at the trimmer line spool, wherein the counter is continuously actuatable by the ring gear at the trimmer line spool. By use of a ring gear, an extremely precise determination of the relative rotation between trimmer line spool and housing and thus of the trimmer line length that is wound onto the trimmer line spool is enabled. 
     It is advantageously provided that the actuating element is a pulse generator arranged at the trimmer line spool, wherein the counter is embodied as a pulse counter for recording the pulses that are emitted by the at least one pulse generator. The pulse counter is preferably an optical sensor, in particular an inductive or a capacitive proximity sensor. In this configuration, the counting process can be realized without mechanical contact between the actuating element and the counter. The counter is preferably embodied as a rotary encoder. In this way, a precise indication of the rotation angle can be provided. 
     The counting device comprises preferably an output element coupled with the counter, wherein the counter value which is determined by the counter is indicated at least indirectly by the output element. The output element is preferably arranged on the housing so as to be visible by the operator of the trimmer head. In this way, the operator can detect how much residual trimmer line length is still wound on the trimmer line spool even in the installed state of the trimmer line spool. 
     The counting device is preferably configured such that the counting device has a zero position when the trimmer line has been unwound from the trimmer line spool. When winding trimmer line onto the trimmer line spool, the counter counts up so that the operator based on the output element can recognize the trimmer line length that has been wound onto the spool. Upon unwinding the trimmer line from the trimmer line spool, the trimmer line spool is rotated in relation to the housing in the second rotational direction and the counter counts down until the trimmer line has been completely unwound and the counting device has again reached the zero position. 
     It is preferably provided that the trimmer line spool comprises at least one continuous trimmer line channel through which the trimmer line can be pushed and then wound onto the spool. For winding the trimmer line, the trimmer line has to be pushed through the trimmer line channel and subsequently the trimmer line spool is to be rotated in the first direction relative to the housing. Preferably, the trimmer line spool comprises at least two holding devices for fastening two trimmer lines. In this way, one trimmer line can be fixed at each holding device and the trimmer lines can be subsequently wound onto the trimmer line spool. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Further features of the invention result from the description and the drawing. Embodiments are illustrated which will be described in detail in the following. 
         FIG. 1  is a schematic illustration of a trimmer held by an operator. 
         FIG. 2  is a side view of an embodiment of a trimmer head with residual trimmer line indicator. 
         FIG. 3  is a section illustration of the trimmer head according to  FIG. 2 . 
         FIG. 4  is a schematic illustration of an embodiment of a trimmer head with mechanical counter. 
         FIG. 5  is a schematic illustration of an embodiment of a trimmer head with electromechanical counter. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows a trimmer  1  in a schematic illustration. The trimmer  1  is held by an operator  30 . The trimmer  1  comprises a rearward end with a rearward housing  31  and a front end from which a drive shaft  3  ( FIG. 2 ) projects. A shaft  32  connects the rearward end and the front end. Handles  55  for guiding the trimmer  1  are arranged at the shaft  32 . A trimmer head  2  adjoins the front end of the trimmer  1 . The trimmer head  2  is fastened to the drive shaft  3  and is driven in rotation about an axis of rotation  7  by a drive motor  33 , only schematically indicated, in a rotational direction  34  for work. The drive motor  33  is arranged in the rearward housing  31  wherein a drive shaft is extending in the shaft  32 . It can be provided that this drive shaft is connected inside the shaft immediately to the drive shaft  3  for the trimmer head  2  so that no gearbox is positioned inbetween. In an alternative embodiment, not illustrated, the drive motor  33 , which is in particular an electric motor, can also be arranged at a front housing, not illustrated, that is arranged at the front end. Advantageously, in the front housing there is also a gear box of the trimmer head  2 . The trimmer head  2  is provided with a protective shield  35  at the side which is facing the operator  30  in operation. The trimmer head  2  comprises at least one tool, which is a trimmer line  6  in the embodiment, for cutting things such as grass, shrubs or the like. A bottom side  37  is formed at the trimmer head  2  and faces the ground  36  in operation; it is arranged at the side of the trimmer head  2  facing away from the shaft  32 . At the side of the trimmer head  2  which is facing the shaft  32 , the top side  38  of the trimmer head  2  is formed. Protective gear that has to be worn mandatorily by the operator  30  for operating the trimmer  1  is not illustrated in the simplified illustration of  FIG. 1 . 
     In  FIG. 2 , the trimmer head  2  is illustrated in a side view. The trimmer head  2  comprises an axis of rotation  7  about which the trimmer head  2  is rotated in operation of the trimmer  1 . For this purpose, the trimmer head  2  is driven by the only schematically illustrated drive shaft  3 . In addition, the trimmer head  2  comprises a housing  4  and a trimmer line spool  5  ( FIGS. 3 to 5 ) arranged in the housing  4 . The housing  4  of the trimmer head  2  is cup-shaped and comprises in the embodiment a cover member  39  and a circumferential wall  40 . The cover member  39  extends, beginning at the axis of rotation  7 , in radial direction of the axis of rotation  7 . The cover member  39  in the embodiment is oriented approximately perpendicularly to the axis of rotation  7  of the trimmer head  2 . The circumferential wall  40  adjoins the cover member  39  and extends in the direction of the axis of rotation  7 . At the circumferential wall  40  of the housing  4 , two oppositely positioned trimmer line openings  41  are provided through which the trimmer line  6  projects out of the housing  4 . The trimmer head  2  comprises in the embodiment a housing cover  42  that is fastened by two snap-on connections  43  at the housing  4 . By means of the housing cover  42 , the components arranged in the housing  4  are secured in the housing and protected from becoming soiled. 
     As illustrated in  FIG. 3 , the trimmer line spool  5  is rotatably supported in relation to the housing  4  about the axis of rotation  7 . The trimmer line spool  5  comprises at least one spool chamber  45 ,  45 ′ for winding a trimmer line  6  therein. In the preferred embodiment according to  FIG. 3 , the trimmer line spool  5  comprises two spool chambers  45 ,  45 ′ arranged one after the other in the direction of rotation  7  into which a trimmer line  6  can be wound, respectively. The trimmer line spool  5  comprises a first spool wall  46 , a second spool wall  48 , and an intermediate wall  47  arranged between the first spool wall  46  and the second spool wall  48 . The trimmer line spool  5  comprises moreover a longitudinal wall  49  that connects the first spool wall  46 , the intermediate wall  47 , and the second spool wall  48  with each other. One of the two spool chambers  45  is delimited in the direction of the axis of rotation  7  by the first spool wall  46  and the intermediate wall  47 . In radial direction in relation to the axis of rotation  7 , the spool chamber  45  is delimited by the longitudinal wall  49 . The other one of the two spool chambers  45  is delimited in the direction of the axis of rotation  7  by the intermediate wall  47  and the second spool wall  48 . In radial direction relative to the axis of rotation  7 , the other spool chamber  45 ′ is delimited by the longitudinal wall  49 . 
     For winding the trimmer line  6  on the spool, the trimmer line spool  5  has a continuous trimmer line channel  54  through which the trimmer line  6  can be pushed and then wound onto the spool. Such a continuous trimmer line channel  54  enables the operator to wind the trimmer line  6  onto the spool in the mounted state of the trimmer head  2 . In such a state, the trimmer line spool  5  is held in the housing  4  of the trimmer head  2 . The operator pushes the trimmer line  6  into the trimmer line channel  54  and aligns it in such a way that trimmer line ends of approximately the same length project from the trimmer line channel  54  at the respective ends of the trimmer line channel  54 . Subsequently, the trimmer line spool  5  is rotated in a first rotational direction in relation to the housing  4 . Each free end of the trimmer line  6  then is wound into one of the spool chambers  45 ,  45 , respectively. In the embodiment, such a trimmer line channel  54  is provided in the intermediate wall  47  of the trimmer line spool  5 . 
     Instead of or in addition to the trimmer line channel  54 , the spool chambers  45 ,  45 ′ can be provided with trimmer line holders at which a respective trimmer line  6  can be held. The trimmer line  6  is fixed at the trimmer line holder and, by a rotation of the trimmer line spool  5  relative to the housing  4 , is subsequently wound onto the trimmer line spool  5  in one of the spool chambers  45 ,  45 ′. In this way, several trimmer lines  6  can be wound onto the trimmer line spool  5 . 
     When in operation of the trimmer head  2  the trimmer line  6  is worn at its ends, it must be unwound from the trimmer line spool  5  for lengthening the ends extending from the housing  4 . For this purpose, the trimmer head  2  comprises an indexing device  50 . As illustrated in  FIG. 3 , the indexing device  50  is comprised of a plurality of locking contours  51 . The locking contours  51  have the effect that in an operational position of the trimmer head  2  the trimmer line spool  5  is fixedly connected to the housing  4  for common rotation in the working rotational direction  34 . For unwinding the trimmer line  6  from the trimmer line spool  5 , the fixed connection of the locking contours  51  between trimmer line spool  5  and the housing  4  must be canceled and subsequently the trimmer line spool  5  rotated in the second rotational direction  9  opposite to the working rotational direction  34  about the axis of rotation  7  relative to the housing  4 . The second rotational direction  9  is opposite to the first rotational direction  8 . In the embodiment, the connection between the locking contours  51  can be canceled by an actuating device  52  projecting through the housing cover  42 . The actuating device  52  is to be pushed in the direction of the axis of rotation  7  toward the cover member  39  of the housing  4 . This can be realized by hitting the trimmer head  2  against the ground  36 . In doing so, the trimmer line spool  5  is lifted in the direction of the axis of rotation  7  so that the locking contours  51  release. The housing  4  rotates further; by release of the rotational connection, the trimmer line spool  5  rotates relative to the housing  4  and the trimmer line  6  is unwound. By a spring element  53 , the trimmer line spool  5  is pushed back into the locked position after a predetermined angle rotation so that the rotational connection between the trimmer line spool  5  and housing  4  is reinstated. 
     In an alternative embodiment, the indexing device  50  can also be designed such that, for canceling the rotational connection between the trimmer line spool  5  and the housing  4 , the trimmer line spool  5  must be pulled in the direction away from the cover member  39  of the housing  4  in the direction of the axis of rotation  7 . Subsequently, the trimmer line spool  5  is to be rotated by hand relative to the housing  4  in order to unwind the trimmer line  6  from the trimmer line spool  5 . 
     As illustrated in  FIGS. 4 and 5 , the trimmer head  2  comprises a counting device  10 . The counting device  10  serves to detect the relative rotation of housing  4  and trimmer line spool  5  and, by means of an output element  12  coupled therewith, to indicate to the operator how much residual trimmer line length is still wound on the trimmer line spool  5 . The output element  12  can be coupled to the counter mechanically, electromechanically or electronically. Removal of the trimmer line spool  5  from the housing  4  or demounting the trimmer head  2  is not required for this. In this way, the operator can be informed in a simple way of the point in time when a new trimmer line  6  is presumably to be wound onto the trimmer line spool  5 . Thus, it is possible for the operator to take care of procuring a new trimmer line in due time. 
     For winding the trimmer line  6  onto the trimmer line spool  5 , the trimmer line spool  5  is to be rotated in the first rotational direction  8  about the axis of rotation  7  relative to the housing  4 . For unwinding the trimmer line  6  from the trimmer line spool  5 , the trimmer line spool  5  is to be rotated in the second rotational direction  9  opposite to the first rotational direction  8 . 
     As illustrated in  FIGS. 4 and 5 , the counting device  10  comprises a counter  11  and an output element  12  coupled with the counter  11 . The counter  11  is preferably arranged at the housing  4 . The counter  11  is operatively connected to the trimmer line spool  5  such that the counter  11  counts up upon relative rotation between trimmer line spool  5  and housing  4  in the first rotational direction  8  and counts down in the second rotational direction  9 . The counter  11  is designed such that the counter  11  is in a zero position when there is no trimmer line  6  wound on the trimmer line spool  5 . For winding the trimmer line  6  onto the trimmer line spool  5 , the operator rotates the trimmer line spool  5  in the mounted state of the trimmer head  2  relative to the housing  4  in the first rotational direction  8 . In doing so, the counter  11  counts at least each individual relative revolution of the trimmer line spool  5  relative to the housing  4 . In an alternative embodiment of the trimmer head  2 , the trimmer head  2  can also be designed such that the relative movement between trimmer line spool  5  and housing  4  for winding the trimmer line  6  onto the spool  5  is effected by a motor, in particular by the drive motor. When the trimmer line  6  is unwound from the trimmer line spool  5 , the trimmer line spool  5  is rotated in the second rotational direction  9  relative to the housing  4 , wherein in this direction the counter  11  counts down. The counter value which is generated by the counter  11  is transmitted to the output element  12  which is embodied in particular as an indicator element wherein the output element  12  communicates the counter value to the operator. The counter value is transmitted by the output element  12  acoustically and/or visually. 
     Upon winding the trimmer line  6  onto the spool, the counting device  10  provides for initializing the length of the trimmer line  6 . Accordingly, the length of a trimmer line  6  is determined. Therefore, the use of a trimmer line of a predetermined length is not required for a correct determination of the residual trimmer line length. It is possible for the operator to use trimmer lines of various lengths. 
     The counter  11  can be a mechanical, in particular an electromechanical, preferably electronic counter  11 . In the embodiment of the counter  11  as a mechanical counter, preferably an actuating element  13 , here embodied as a tooth element, is provided at the trimmer line spool  5  and actuates the counter  11  with each revolution. A compensation weight  14  for an imbalance-free weight distribution of the trimmer head  2  is provided for the counting device  10 . Such a compensation weight  14  can be designed as simple weighting elements. Also, a second counting device with output element is conceivable that is designed to be symmetrical to the first counting device  10  in relation to the axis of rotation  7 . 
     In addition, in an alternative embodiment according to the invention of the trimmer head  2 , it can be expedient to distribute a plurality of actuating elements  13  at the trimmer line spool  5  in the circumferential direction of the axis of rotation  7  in order to actuate the counter  11  several times per revolution. With increasing number of actuating elements  13 , a more exact determination of the residual trimmer line length is possible. Alternatively, a ring gear can be provided instead of individual tooth elements at the trimmer line spool  5 , wherein the ring gear is operatively connected to the counter  11 . Preferably, a gear unit is provided between the counter  11  and the ring gear so that a continuous determination of the residual trimmer line length is possible. The counter  11  is illustrated schematically in  FIG. 4  as a gear wheel which is supported in the housing  4 . Of course, as a counter  11  typical counters such as roller counters, quantity counters can be used. 
     In an alternative embodiment of the trimmer head  2 , the counter of the counting device  10  can be embodied as an electromechanical or electronic counter. As shown in  FIG. 5 , the actuating element  13  that is provided at the trimmer line spool  5  can also be configured as a pulse generator. The counter  11  is designed as a pulse counter. The pulse counter can be an inductive proximity sensor, a capacitive proximity sensor but also an optical sensor. For a more precise resolution and determination of the residual trimmer line length, a rotary speed encoder can be provided also as a counter  11 . For determining whether the trimmer line spool  5  is rotating in a first rotational direction  8  or a second rotational direction  9 , the pulse generator is preferably configured such that the detected pulse is designed nonuniform. In this way, the rotational direction of the trimmer line spool  5  can be detected based on the pulse signal. 
     As shown in  FIGS. 4 and 5 , the output element  12  is arranged at the housing  4 . In the embodiment, the output element  12  is arranged at the circumferential wall  40  of the housing  4 . However, it can also be expedient to arrange the output element  12  on the cover member  39  of the housing  4 . The output element  12  is arranged at the housing  4  such that it is possible for the operator to recognize the output element  12  in the mounted state of the trimmer head  2  so that the operator can derive the residual trimmer line length of the trimmer line  6  based on the information provided by the output element  12 . 
     As illustrated in  FIGS. 4 and 5 , the output element  12  is coupled with the counter  11  for indicating the residual trimmer line length. In case of a mechanical counting device  10 , the output element  12  can be, for example, a slider element  15 . The slider element  15  is displaced by the counter  11 . A marking  17  is provided on the slider element  15 . By means of an indicator region  16  of the output element  12 , the operator can view the slider element  15 . Based on the position of the marking  17  provided on the slider element  15 , the operator can detect how much residual trimmer line length of the trimmer line  6  is still wound on the trimmer line spool  5 . The indicator region  16  can be provided, for example, by an opening provided in the housing  4  or by a transparent housing section. The marking  17  of the slider element  15  can be formed also by a combination of various color gradations of the slider element  15 , for example, green, yellow, red. Also, other markings  17  are conceivable that can indicate the residual trimmer line length to the operator. Instead of a marking  17 , also numerals can be provided that represent the number of actuations or the remaining residual trimmer line length as a unit of measure. In this embodiment variant, the output element  12  is mechanically coupled with the counter  11 . The slider element  15 , its marking  17 , and the indicator region  16  are components of the output element  12 . 
     As illustrated in  FIG. 5 , in case of an electromechanical counter  11  the counted pulses are processed by a control unit  18  and transmitted to the output element  12 . The output element  12  in this embodiment is preferably configured as a digital display. The pulses which are detected by the counter  11  are output as a numerical value. 
     Alternatively, a computational conversion, based on the diameter of the trimmer line spool  5 , to the actual residual trimmer line length can be realized so that the output element  12  indicates the residual trimmer line length as a unit of length. 
     In an alternative embodiment, it can be expedient to design the trimmer head  2  such that the counter  11  is fixedly connected to the trimmer line spool  5  and the actuating element  13  is fixedly connected to the housing  4 . 
     The specification incorporates by reference the entire disclosure of European priority document 19 218 095.8 having a filing date of Dec. 19, 2019. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.