Classifications

• • A—HUMAN NECESSITIES
  • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
  • A01G—HORTICULTURE; CULTIVATION OF VEGETABLES, FLOWERS, RICE, FRUIT, VINES, HOPS OR SEAWEED; FORESTRY; WATERING
  • A01G3/00—Cutting implements specially adapted for horticultural purposes; Delimbing standing trees
  • A01G3/04—Apparatus for trimming hedges, e.g. hedge shears
  • A01G3/047—Apparatus for trimming hedges, e.g. hedge shears portable
  • A01G3/053—Apparatus for trimming hedges, e.g. hedge shears portable motor-driven

Definitions

• the present invention relates to a cutting tool . More particula rly, it relates to a cutting tool with at least one oscillating cutting blade.
• a cutting tool like a hedge trimmer includes a motor, a pair of cutting blades, and a gearbox assembly.
• the cutting blades of the hedge trimmer are placed adjacent to each other in a superimposed relationship, such that the cutting blades are arranged to reciprocate relative to each other along a longitudinal axis.
• Each of the cutting blades has multiple cutting teeth which a re aligned orthogonal to the longitudinal axis.
• both the cutting blades may be driven by a motor.
• one of the cutting blades may be driven whereas the other blade may be stationary.
• the motor of the hedge trimmer is connected to a battery or another power sup- plying means to operate the cutting blades.
• hedge trimmers may encounter a thick or hard branch which gets stuck between two cutting teeth .
• the operator may try to pull the branch trapped between two cutting teeth. This poses a safety concern as the operator puts his finger near the cutting blades. It is thus advisable to switch off the power to the cutting blades to remove the pressure of the moving blade on the branch before attempting to remove the stuck branch . Repeated encounters of a thick branch might force the operator to frequently turn the hedge trimmer off. This makes operating the hedge trimmer incon- venient.
• an objective is to provide an i nexpensive and simplified system for reversing an output direction of a cutting tool .
• the cutting tool includes at least one cutting blade which is adapted to perform an oscil lating movement.
• the cutting tool also includes a prime mover to drive the at least one cutting blade such that an output direction of the prime mover is selectively reversible. Further, the output direction of the prime mover is periodically switched with a predetermined time period. Thus, a direction of oscillation of the cutting blade periodically changes. This may result in a continuous chopping action on an external body stuck between the cutting teeth and severe the body within a one or more predetermined time periods.
• the cutting blade moves at least a minimum distance within the predetermined time period .
• a gap between cutting teeth of the blades is maximum at least once within the predetermined time period . This enables a user to safely re- move the body stuck between the cutting teeth if the body is not severed .
• the output direction of the prime mover is periodically switched during a switching mode. Further, preferably, a minimum time interval is provided between two consecutive switching modes.
• the cutting tool includes an actuator, the actuator being configured to initiate the switching mode. Further, preferably, the switching mode initiates and continues for a first duration once the actuator is pressed . Alternatively, preferably, the switching mode initiates and continues when the actuator is kept pressed. Moreover, in another embod i- ment, the switching mode terminates after a second duration.
• the first duration and the second duration are integral multiples of the predetermined time period.
• the present invention does not requi re sensors, or any other electronic equipment to sense a blockage and effect a reversal in the output direction.
• user reverses the output direction whenever there is a blockage.
• this may simplify the construction and reduce the cost of the cutting tool .
• the switching mode is terminated if a cu rrent in the prime mover exceeds an upper limit. This safeguards various components of the prime mover against damage. Further, according to another embodiment, the switching mode is terminated if the current in the pri me mover is below a lower limit during the predetermined time period. If the current is below the lower limit, it indicates that any blockage if present has been removed, and the cutting blade can function normally. Alternatively, according to another embodiment, the switching mode is terminated if a load in the pri me mover exceeds an upper limit. Further, accordi ng to another embodiment, the switching mode is terminated if the load in the prime mover is below a lower limit during the predetermined time period .
• the prime mover includes a gear system, the gear system being adapted to periodically switch the output direction of the prime mover.
• the prime mover includes an electric motor.
• the prime mover includes two electric motors, and freewheeling clutches are provided between the electric motors and the cutting blade such that each electric motor drives the cutting blade i n a single direction .
• each electric motor alternately drives the cutti ng blade during the predetermined ti me periods.
• the cutting tool is one of a hedge trimmer or a shrub shear.
• Claim 9 discloses a method of operating a cutting tool .
• the cutting tool includes at least one cutting blade adapted to perform an osci llating movement.
• a prime mover is provided to drive the at least one cutting blade, an output direction of the prime mover being selectively reversible.
• the output direction of the prime mover is periodically switched or reversed with a predetermined time period (or switching or reversing period).
• a monitoring step is performed wherein the electrical current of or for the prime mover is monitored (or: measured, detected) during a defined monitoring time interval of or within the time period, wherein the monitored (or: measured, detected) current is compared with a predetermined threshold value (or: threshold current or level) and, when the monitored current is below the threshold value, the switching or reversing of the output direction of the pri me mover is deferred or interrupted and/or the output d irection of the pri me mover is maintained or kept unchanged in a so called normal operation mode or one-directional mode.
• a predetermined threshold value or: threshold current or level
• the threshold value is preferably chosen from an interval between 10 % and 50 %, preferably 10 % to 33 %, of the maximum current or initial current peak which is reached immediately after a switch ing or reversing action of the output direction of the prime mover.
• the defined measuring time interval is at least the last qua rter, preferably at least the last third, of the time period of the switchi ng or reversing or of the time interva l between two potential switching or reversing actions of the output direction of the prime mover.
• the defined measuring time interval corresponds to the difference between said time period or said ti me interval and a given waiting time interval, in particular 0.2 s That way an initial peak of the current resulting from the load right after the reversing or switching will normal ly not be in the monitoring interval a nd, thus, not be detected.
• the monitoring time interval is in particula r chosen from an interva l between 0.05 s to 1 s, in particula r between 0.2 s and 0.5 s.
• the monitoring step is performed by detecting the rotation of the motor and/or the movement of the prime mover or an oscillating blade. In this case the detection reveals that there is no interruption of the rotation of the motor or in the movement of the oscillating blade during the monitoring interval one can conclude that there is no jamming or blockage of the blades.
• the monitoring takes place during a time interval (monitoring interval) immediately preceding the end of the predetermined time period (214) in which the output direction of the prime mover is periodically switched du ring a switching mode (210).
• the method can comprise the following further steps:
• FIG. 1 illustrates a schematic view of a cutting tool, according to an embodiment of the present invention
• FIG. 2 illustrates a plot of displacement of a cutting blade against time, according to an embodiment of the present invention
• FIG. 3 illustrates a schematic view of the cutting tool, according to an alternative embodiment of the present invention
• FIG. 4 illustrates a plot of displacement of the cutting blade against time, accord ing to another embodiment of the present invention
• FIG. 5 exemplary diagrams showing the change in current as drawn by the motor in normal mode and under blockage
• FIG. 6 shows a flowchart of a preferred mode of operation.
• FIG. 1 shows a schematic view of a cutting tool 100, according to an embodiment of the present invention.
• the cutting tool 100 may be, for example, but not limited to, a hedge trimmer, a shrub shear, or the like. In addition, any suitable size, shape, or type of elements or materials could be used.
• the cutting tool 100 includes a cutting unit 102 and a prime mover 104.
• the prime mover 104 may be housed inside a body, while the cutting unit 102 may be connected to a front portion of the body.
• the cutting tool 100 may include one or more handles to permit a user to grasp the cutting tool 100 during operation. Further, the cutting tool 100 may in- elude a manually actuated trigger to activate or deactivate the prime mover 104.
• the cutting unit 102 includes a cutting blade 106 (hereinafter referred to as "the blade 106") adapted to perform an oscillating movement and driven by the prime mover 104.
• the oscillating movement may be a linear oscillating movement or an angular oscillating movement about an axis.
• the blade 106 may have multiple cutting teeth which extend substan- tially perpendicular relative to a direction of linear oscillation of the blade 106.
• the cutting teeth may extend in a plane which is substantia lly perpendicular relative to the axis of oscillation.
• another blade 107 may be provided .
• the blade 107 also includes multiple cutting teeth and disposed in a superimposed relationship with the blade 106.
• the blade 107 is stationary.
• the blade 107 also oscillates with the blade 106. Cutting is performed by shearing action between the cutting teeth of the blades 106 and 107.
• the prime mover 104 includes an electric motor 108 (hereinafter referred to as "the motor 108").
• the motor 108 may be an AC or DC motor within the scope of the present invention .
• the motor 108 may be driven by a battery or di rectly from an external power source.
• the prime mover 104 may include two motors (expla ined in detail in conjunction with FIG. 3).
• the motor 108 d rives a transmission unit 110 which in turn imparts the oscillating movement to the blade 106.
• the transmission unit 110 may include any combination of one or more gears, eccentric members, friction drive, belt- pulley drive, or the like within the scope of the present invention .
• the transmission unit 110 includes a gear system 111 adapted to selectively switch an output direction of the prime mover 104.
• the output direction of the prime mover 104 may be reversed by any other means, for example, an electronic circuit.
• the motor 108 may be a brushless DC motor whose direction is reversed by using a reversible drive circuit.
• Such a reversible drive circuit may be simila r to the reversible drive circuit described in US Pat. 4,282,464 titled "Reversible drive circuit for brushless DC motor", the disclosure of which is incorporated herein by reference.
• the motor 108 may be a brushed DC motor which may be reversed using a switch circuit, for example, the switch circuit de- scribed in US Pat. 5,877,573 titled “D.C. motor and reversing circuit", the disclosure of which is incorporated herein by reference.
• an actuator 112 is provided to initiate a switching mode (explained in detail in conjunction with FIG. 2) of the cutting tool 100.
• the actuator 112 may be a manually actuated switch provided on the body of the cutting tool 100 for easy accessibility. Further, the switch may be provided in a recessed area to prevent accidental actuation . In an embodiment of the present invention, the actuator 112 may also act as a trigger for acti- vation and deactivation of the prime mover 104. Further, the actuator 112 may be a toggle switch movable between three positions. The first position corresponds to an off state of the toggle switch . In the second position, the toggle switch may activate the prime mover 104 while in the third position the toggle switch may initiate the switching mode.
• the actuator 112 may be a push button switch that can be pressed into two different positions from an off position .
• the two positions may correspond to the activation of the prime mover 104 and the initiation of the switching mode respectively.
• a trigger for activating and deactivating the pri me mover 104 may be separate from the actuator 112.
• FIG. 2 shows a plot 200 illustrating displacement of the blade 106 against time, according to an embodiment of the present invention.
• the va riation of displacement with time of the blade 106 is shown to be substantially sinusoi- da l in nature purely for exemplary purposes, and the displacement may vary in any other manner with time within the scope of the present invention .
• duri ng a normal operational mode 202 of the cutting tool 100
• the blade 106 is shown to oscillate between extreme positions 204 and 206.
• the extreme position 204 is assigned a zero value.
• a distance 208 between the ex- treme positions 204 and 206 is the range of oscillation of the blade 106.
• a gap between the cutting teeth of the blades 106 and 107 is also maximum at the extreme positions 204 and 206.
• the blade 106 oscillates with a normal time period 209.
• the output direction of the prime mover 104 is always in a specific direction in the normal operational mode 202.
• the specific direction may be same as a normal direction of rotation of the motor 108.
• the blades 106 and 107 may become jammed when any large body (E.g., a branch) gets stuck between the cutting teeth of the blades 106 and 107. As shown in FIG. 2, the blades 106 and 107 get jammed at point 211. In such a case, the user may move the actuator 112 to initiate a switching mode 210 of the cutting tool 100. On initiation of the switching mode 210 at point 212, the output direction of the prime mover 104 does not change for a predetermined time period 214, and the blades 106 and 107 re- main jammed. After the time period 214 is over, the gear system 111 reverses the output direction of the prime mover 104 at point 213.
• any large body E.g., a branch
• the direction of oscillation changes at the point 213.
• the direction of oscillation is periodically changed with the time period 214 during the switching mode 210.
• the blockage is removed after the blades 106 and 107 are jammed twice during the switching mode 210 after the point 213.
• the user may remove the body.
• the output direction of the prime mover 104, after the termination of the switching mode 210 is same as the direction at the start of the switching mode 210. Therefore, the output direction of the prime mover 104 after point 218 is same as the output direction of the prime mover 104 before the point 213.
• the motor 108 is a brushed DC motor
• the output direction of the prime mover 104, before the point 213 and after the point 218, may be same as the normal direction of rotation of the motor 108.
• the time period 214 is at least half of the normal time period 209 such that the blade 106 moves at least the distance 208 within the time period 214.
• the cutting blade 206 moves through one of the extreme positions 204 or 206 within the time period 214.
• a gap between the cutting teeth of the blades 106 and 107 is maximum at least once within the time period 214. This enables the user to safely remove the body stuck between the cutting teeth if the body is not severed by the continuous chopping action of the blades 106 and 106.
• the time period 214 may be any value greater than half the normal time period 209 and may be equal to the normal time period 209.
• the reversal in the output direction also reduces impact forces on the blades 106 and 107, and prevents transmission of impact forces to various components of the cutting tool 100, such as, the motor 108 and the transmission unit 110.
• the present invention also does not require sensors, or any other electronic equipment to sense a blockage and effect a reversal in the output direction.
• user reverses the output direction whenever there is a blockage.
• this may simplify the construction and reduce the cost of the cutting tool 100.
• the user may switch off the prime mover 104 on detecting a jamming of the blades 106 and 107. Subsequently, the prime mover 104 is switched on in the switching mode 210.
• the output direction of the prime mover 104 during the first cycle of the switching mode 210 may be same as the output direction which was prior to the deactivation of the prime mover 104. Alternatively, the output direction of the prime mover 104 may be opposite to the output direction which was prior to the deactivation of the prime mover 104.
• the prime mover 104 may operate in the normal operational mode 202. Alter- natively, the user may switch off the prime mover 104 and switch on the prime mover 104 in the normal operational mode 202.
• the switching mode 210 auto- matically continues for a first duration 216 after the actuator 112 is moved to the switching mode position and released.
• the first duration 216 is a predetermined duration such that various components of the prime mover 104 do not get overheated due to frequent reversal in the direc- tion of output.
• the first duration 216 is also an integral multiple of the time period 214 so that the blade 106 completes an oscillation cycle of the switching mode 210 before reverting back to the normal operational mode 202.
• the switching mode 210 continues as long the actuator 112 is retained in the switching mode position.
• the blade 106 When the user releases the actuator 112 from the switching mode position, the blade 106 completes the current oscillation cycle of the switching mode 210 before reverting back to the normal operation mode 202. However, in case the user keeps the actuator 112 in the switching mode position beyond a second duration, the switching mode 210 is automatically terminated.
• the second duration of the switching mode 210 is also an integral multiple of the time period 214. In an embodiment of the present invention, the second duration is equal to the first duration 216. Further, in another embodiment of the present invention, a minimum time interval is provided before another switching mode 210 can be initiated. The minimum time interval enables various components of the prime mover 104 to sufficiently cool down before another switching mode 210.
• a current limiter (not shown in the figures) may be provided to limit the current flowing in the motor 108. In case the current exceeds an upper limit, the switching mode 210 is terminated . Su bseq uently, the prime mover 104 may be switched off. In a further embodiment of the present i nvention, if the current is below a lower limit during any of the time periods 214, the switching mode 210 is terminated . If the current is below the lower limit, it ind icates that the blockage is removed, and the blades 106 and 107 can function normally. In yet another embodiment of the present invention, a load limiter (not shown in the figures) may be provided to limit the load in the motor 108. In case the load exceeds an upper limit, the switching mode 210 is terminated. Moreover, if the load is below a lower limit during any of the time periods 214, the switching mode 210 is terminated .
• the actuator 112 may be a conventional switch used for activati ng and deactivating the motor 108.
• the switching mode 210 is initiated on switching on the motor 108. Subsequently, the switching mode 210 is terminated if the current or load in the motor 108 is below a lower limit after a certain time period, preferably the time period 214, and the normal operational mode 202 is started .
• the oscil lation of the blade 107 is displaced by about half of the normal time period 209 d uring the normal operational mode 202.
• the oscillating d irection of the blade 107 is also periodically reversed with a time period 214. Further, the oscillation of the blade 107 is also displaced by half of the time period 214.
• FIG. 3 illustrates the cutting tool 100, accordi ng to another embodiment of the present invention .
• the prime mover 302 includes two motors 304A and 304B, and corresponding freewheeling clutches 306A and 306B which form part of the transmission unit 308.
• each of the freewheeling clutches 306A and 306B is provided between the motors 304A and 304B respectively, such that each of the motors 304A and 304B drives the blade 106 in a single direction .
• any one of the motors 304A and 304B may drive the blade 106
• the motor 304A drives the blade 106 during the operational mode 202.
• each of the motors 304A and 304B alternatively drives the blade 106 during the time periods 214
• FIG. 4 illustrates a plot 400 illustrating displacement of the blade 106 against time, according to another embodiment of the present invention.
• the plot 400 illustrates the cutting tool 100 which operates solely in the switching mode.
• the cutting tool 100 may be of a similar construction as the embodiment illustrated in FIG. 3.
• the output direction of the prime mover 302 changes after each time period 402.
• the blades 106 and 107 get jammed at point 404.
• the blade 106 again oscillates as the output direction of the prime mover 302 changes in the next cycle.
• the blades 106 and 107 get jammed after reaching the blockage position during the cycle. Subsequently, the blockage is removed after the blades 106 and 107 are jammed thrice.
• the output direction of the prime mover 302 during the first cycle may be same as the output direction which was prior to the deactivation of the prime mover 302.
• the output direction of the prime mover 302 may be opposite to the output direction which was prior to the deactivation of the prime mover 302.
• the first condition to be checked is whether the trigger switch such as the actuator 112 is turned on.
• the actuator 112 may also act as the trigger for activation and deactivation of the prime mover. If so (“YES”) the drive of the motor is started in reversing mode, preferably in the same direction the motor stopped or was switched off the last time.
• the monitoring takes place during a time interval (monitoring interval) immediately preceding the end of the predetermined time period (214) in which the output direction of the prime mover is periodically switched d uring a switching mode (210).
• the threshold current or value is preferably chosen to be a pproximately in the area between on half ( 1/2) and one third (1/3) of the maximum current or initial peak value of the current mentioned above and occurring immed iately after a switching operation or can be in absolute terms about 15 A. Other values in relative or absolute terms are of course a lso possible subject to specific embodiments.
• the motor current should fall below the threshold value and no reversing switching operation occurs a ny more, i .e. the actual direction is maintained and, further on, a normal operation mode without reversing takes place or is performed.
• the reversing mode is continued until either the 5s or 15 cycles are completed or a drop of the current below the threshold value is detected within the monitoring time period of the next time period or cycle, i .e. the jamming or clamping was resolved or ceased.
• the trigger switch is turned off (again). If "YES”, the drive of the motor is stopped and it is returned to the first condition, i .e. checking whether the trigger switch is switched on .
• the second condition that is the check if a given ti me limit has lapsed which allows to reduce the risk of overload
• the actuator 112 that initiates the switching mode 210 is identical with the trigger that is activating and deactivating the movement of the prime mover if the cutting tool. This means that immediately after the activation of the cutting tool the tool will find itself in the switching or reversing mode 210.
• the monitoring step would immediately after the start of the cutting tool detect whether or not there is a jamming or blockage of the blades. If so, the cutting tool would work in the switching or reversing mode trying to cease the jamming or blockage. If not, the cutting tool would automatically end the switching mode and change to normal operation. It is of advantage if in a non-blockage situation the detection during the monitoring step works that fast that the switching mode could automatically be ended already within the first predetermined time period after activation of the cutting tool. In this case the user would not even recognize the change from the switching mode into the normal working mode of the cutting tool.
• the cutting tool 100 may include a single motor which always oscillates in the switching mode.
• a reversing mechanism may be provided to periodically change the output direction of the motor. Examples of such a reversing mechanism may include the one described in US Pat. 4,315,170 (the 3 ⁇ 4 170 patent) titled “Reversible electric motor", the disclosure of which is incorporated herein by reference. The reversing mechanism disclosed in the '170 patent reverses the direction of a DC motor.
• a mechanical drive may be provided with a unidirectional motor for periodically changing the output direction. Such a mechanical drive may similar to the reversible drive described in US Pat. 4,708,291 titled “Oscillating Sprinkler", the disclosure of which is incorporated herein by reference.

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• 2011
  • 2011-08-17 WO PCT/EP2011/064176 patent/WO2013023696A1/en not_active Ceased
  • 2011-08-17 EP EP11745971.9A patent/EP2744323A1/de not_active Withdrawn

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