Abstract:
A power pruner includes a housing, a motor arranged in the housing, a transmission device connected to the motor, a pair of blades and a trigger which is arranged on the housing and used to control the motor. The pair of blades include a fixed blade and a movable blade which is driven by the motor to swing back and forth. The power pruner additionally includes a stroke switch which is arranged on the housing and has at least two statuses wherein the movable blade has a first stroke when the stroke switch is in a first status and a second stroke different from the first stroke when the stroke switch is in a second status.

Description:
RELATED APPLICATION INFORMATION 
       [0001]    This application claims the benefit of CN 201110080266.8, filed on Mar. 31, 2011, the disclosure of which is incorporated herein by reference in its entirety. 
       BACKGROUND The following generally relates to power pruners and, more particularly, to a power pruner with various strokes. 
       [0002]    A power pruner is widely used as a garden tool because of its small shape and easy portability. The power pruner comprises a pair of blades extending out from a housing, wherein one blade is mounted fixedly to the housing, and the other one is connected pivotably to the fixed blade and driven by a motor to swing back and forth. When pulling the trigger, the motor rotates forwardly to drive the movable blade to swing toward the fixed blade, and then an opening formed between the two blades is closed so as to cut the branches. When releasing the trigger, the motor rotates reversely to drive the movable blade to swing away from the fixed blade, and then the opening is again created. 
         [0003]    The movable blade of the prior art power pruner has only one stroke, that is to say, it can swing only in one angle range, with the blades either being closed or being opened to the largest angle. The opening of such pruner is designed to be so large that it can cut relatively thicker branches. However, during the actual operation, when cutting relatively thinner branches, the stroke of the movable blade (i.e., the swinging angle) is too large for the thin branches, and the movable blade will swing by a certain angle before contacting and cutting the branches, thus a portion of the stroke is essentially an idle stroke, thereby causing the pruning work to be unnecessarily slowed wasting both time and electricity. 
       SUMMARY 
       [0004]    In order to resolve the above defect, the subject power pruner provides two strokes, one for thick branches and thin branches. When pruning thick branches, a first stroke is chosen and the movable blade may open to the largest angle; when pruning thin branches, a second stroke is chosen and the movable blade may open to a middle angle position, thereby avoiding the appearance of the idle stroke and efficiently saving the time of the operator and the electrical quantity of the battery. 
         [0005]    The subject power pruner comprises a housing, a motor arranged in the housing, a transmission device connected to the motor, a pair of blades and a trigger which is arranged on the housing and used to control the motor, wherein the pair of blades include a fixed blade and a movable blade which is driven by the motor to swing back and forth, wherein power pruner also comprises a stroke switch which is arranged on the housing and has at least two statuses, wherein the movable blade has a first stroke when the stroke switch is in a first status and a second stroke different from the first stroke when the stroke switch is in a second status. 
         [0006]    Furthermore, the stroke is the swinging angle of the movable blade, and the movable blade has a first swinging angle when the stroke switch is in the first status and a second swinging angle that is smaller than the first swinging angle when the stroke switch is in the second status. 
         [0007]    Furthermore, the housing may be provided with three position sensors therein for sensing the position of the movable blade. 
         [0008]    Furthermore, the transmission device may comprise a reduction gear box and a bevel gear transmission mechanism, the bevel gear transmission mechanism comprising a driving gear and a fan-shaped driven gear connected to the movable blade. 
         [0009]    Furthermore, the driven gear may be provided with a magnet. 
         [0010]    Furthermore, three position sensors may be used to sense the position of the magnet. 
         [0011]    Furthermore, the trigger may be arranged on the bottom side of the housing, and the stroke switch may be arranged on the top side of the housing opposite to the trigger. 
         [0012]    Furthermore, the stroke switch may be a pushbutton. 
         [0013]    Using such a power pruner may therefore include the following steps: 
         [0014]    a) when cutting thick branches, setting the stroke switch in the first status, then pulling the switch trigger so that the movable blade moves in the first stroke; and 
         [0015]    b) when pruning thin branches, setting the stroke switch in the second status, then pulling the switch trigger so that the movable blade moves in the second stroke. 
         [0016]    Regarding the circuit, the power pruner may comprise a microprocessor, a controlling module for controlling rotation direction of a motor, a power source module and a blade position signal acquisition module for acquiring the position of the movable blade, wherein the power pruner also comprises a stroke switch signal acquisition module for acquiring the position of the stroke switch, wherein the stroke switch is switchable between at least two status, and the microprocessor detects the signal from the stroke switch signal acquisition module so as to control the stroke of the movable blade. 
         [0017]    The method may also comprise the following steps: 
         [0018]    a) pulling the switch trigger whereupon the microprocessor sends a signal to the controlling module to drive the motor to rotate, thereby closing the movable blade; 
         [0019]    b) after the microprocessor detects the signal of closed from the blade position signal acquisition module, the microprocessor controlling the motor to stop rotating until releasing the switch trigger; 
         [0020]    c) after releasing the switch trigger, the microprocessor detects the signal from the stroke switch signal acquisition module, if the stroke switch is in a large stroke position, the microprocessor drives the motor to rotate in the opposite direction by the controlling module, thereby opening the movable blade until detecting the signal of the largest blade opening position from the blade position signal acquisition module; and d) if the stroke switch is in a small stroke position, the microprocessor drives the motor to rotate in the opposite direction by the controlling module, thereby opening the movable blade until detecting the signal of the middle blade opening position from the blade position signal acquisition module. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a perspective view of an exemplary embodiment of a power pruner constructed according to the description that follows; 
           [0022]      FIG. 2  is a section view showing the inner structure of the power pruner of  FIG. 1 ; 
           [0023]      FIG. 3  illustrates a PCB board of  FIG. 2 ; and 
           [0024]      FIG. 4  is a circuit block diagram of the power pruner. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    As shown in  FIG. 1  and  FIG. 2 , a power pruner  10  comprises a housing  1  which is composed of two half housings.  FIG. 2  particularly illustrates one half housing removed to clearly show the inner structure of the power pruner  10 . A battery  2 , a motor  3  and a transmission device are arranged within the housing  1 . The transmission device comprises a reduction gear box  41  and a bevel gear mechanism, the bevel gear mechanism comprising a driving gear  42  and a driven gear  43  that is fan-shaped. A pair of blades  5  and  6  extends out from the housing  1 , wherein the fixed blade  5  is fixedly mounted to the housing  1  by a bolt, and the movable blade  6  is connected pivotably to the fixed blade  5  by a bolt  7 . One end of the movable blade  6  is connected fixedly to the driven gear  43 , thus it can be driven to be swung back and forth in the direction indicated by an arrow D by the motor  3  so as to close and open an opening  60  formed between the two blades. 
         [0026]    A switch trigger  81  and a locking trigger  82  for controlling the motor  3  are arranged on the bottom side of the housing  1 . An interlocking relation is formed between the two triggers, that is to say, the switch trigger  81  can be pressed only after the locking trigger  82  is pressed firstly. A stroke switch  9  for controlling the stroke of the movable blade  6  is mounted on the top side of the housing  1  opposite to the switch trigger  81  and takes the form of a pushbutton. The stroke switch  9  can be adjusted among three positions A, B and C shown in the drawings. When the stroke switch  9  is in the position A, the battery  2  cannot provide power to the motor  3 , and the switch trigger  81  is ineffective; when the stroke switch  9  is in the position B, the movable blade  6  has a large stroke and can swing in a relatively larger angle range α so as to cut the relatively thicker branches; and when the stroke switch  9  is in the position C, the movable blade  6  has a small stroke and can only swing in a relatively smaller angle range β so as to cut the relatively thinner branches. This is plainly illustrated by the dashed lines shown in  FIG. 2 . In the present embodiment, the large stroke has an angle a of approximately 30° for cutting the thick branches with a diameter of 15 mm, and the small stroke has an angle β of approximately 12° for cutting the thin branches with a diameter smaller than or equal to 6 mm. 
         [0027]    Next, the stroke controlling principle of the power pruner  10  will be described. As shown in  FIG. 2  and  FIG. 3 , a magnet  15  is mounted to the driven gear  43  and moves together with the driven gear  43 . A PCB board  14  provided with three position sensors  11 ,  12  and  13  is fixedly mounted in the housing  1  adjacent to the driven gear  43  for sensing the position of the magnet  15 , that is, the position of the movable blade  6 . In the exemplary embodiment, the position sensor is a Hall Sensor. When the position sensor  11  detects the magnet  15 , it indicates that the movable blade  6  is in the closed position; when the position sensor  12  detects the magnet  15 , it indicates that the movable blade  6  is in the largest opening position, that is, the position indicated by the solid line shown in  FIG. 2 ; and when the position sensor  13  detects the magnet  15 , it indicates that the movable blade  6  is in the middle opening position, that is, the position indicated by the dashed line shown in  FIG. 2 . 
         [0028]    As shown in  FIG. 4 , the circuit of the power pruner  10  comprises a microprocessor MCU and its peripheral circuit  20 , a MOSFET controlling module  21  for controlling the rotation direction of the motor  3 , a DC-DC power source module  22 , a blade position signal acquisition module  23  functioned by the position sensors  11 ,  12 ,  13  and the magnet  15  and a stroke switch signal acquisition module  24  for acquiring the position of the stroke switch  9 . When one of the sensors detects the magnet  15 , it sends a signal to the blade position signal acquisition module  23 , thereby acquiring a signal of the position of the movable blade  6 . 
         [0029]    When the stroke switch  9  is in the position A, the power source module  22  does not provide power to the microprocessor MCU  20 , and the pruner  10  is in a power-off state. When the stroke switch  9  is in the position B or C, the battery  2  provides power to the MCU  20  by the power source module  22 , and the pruner  10  is in a power-on state. Then, by pulling the locking trigger  82  and the switch trigger  81 , the MCU  20  sends a signal to the MOSFET controlling module  21  to drive the motor  3  to rotate forwardly so that the movable blade  6  swings toward the fixed blade  5  and the opening  60  is closed; when the MCU  20  detects the signal of closed position from the blade position signal acquisition module  23 , it controls the motor  3  to stop rotating until the switch trigger  81  is released; after releasing the switch trigger  81 , the MCU  20  firstly decide the position of the stroke switch  9  by the stroke switch signal acquisition module  24 , if the stroke switch  9  is in the large stroke position B, the MCU  20  drives the motor  3  to rotate reversely by the MOSFET controlling module  21  so that the movable blade  6  swings in the opposite direction and the opening  60  is opened until the signal of the largest opening position from the blade position signal acquisition module  23  is detected. If the stroke switch  9  is in the small stroke position A, the MCU  20  drives the motor  3  to rotate forwardly by the MOSFET controlling module  21  so that the movable blade  6  swings in the opposite direction until the signal of the middle opening position from the blade position signal acquisition module  23  is detected. 
         [0030]    In the present embodiment, when the power pruner  10  is in the no-load state, it will take approximately 0.8 seconds to open the movable blade to the largest opening position and take approximately 0.5 seconds to open the movable blade to the middle opening position. Therefore, when cutting the thin branches, it will save approximately 0.6 seconds during one pruning process (including the opening and closing of the opening) if the stroke switch is set to the small stroke position C, which efficiently enhances the working efficiency and resolves the problem that the prior pruner could waste the time and the electrical quantity of the battery when pruning the thin branches. 
         [0031]    The above content describes an example embodiment of the invention and discloses a power pruner with two strokes, that is to say, the movable blade has a large stroke and a small stroke, and it can open to the largest opening position or the middle opening position for cutting thick branches and thin branches, respectively. Based on the concept of the invention, in other embodiments, the power pruner may also be designed to have three or more strokes so that the use of the pruner may be further subdivided. Additionally, the sensing method for position of the movable blade is not limited to the above Hall sensor and magnet, and other forms are also feasible, for example, using photoelectric switch or stroke switch. Furthermore, the stroke switch may also use an electronic snapper, which has two positions respectively corresponding to a large stroke and a small stroke, and the stroke switch signal acquisition module is used to acquire the information about the position of the stroke switch.