Abstract:
An electric tool may include an electric motor, a switch operable by a user for adjusting the rotational speed of the electric motor, an operation amount detection device configured to detect the operation amount of the switch, and an operation amount indicating device coupled to the operation amount detection device and configured to indicate the detected operation amount to the user.

Description:
TECHNICAL FIELD 
       [0001]    The present invention mainly relates to a hand-held electric tool such as a screw fastening tool. 
       BACKGROUND ART 
       [0002]    For example, a screw fastening tool (screwdriver) as mentioned above is equipped with a handle portion protruding sidewise from a tool main body portion, and a trigger-type switch lever provided near a base portion (upper portion) of the handle portion so as to be pulled by the user with a fingertip. When this switch lever is pulled, an electric motor mounted within the tool main body portion starts to rotate a screw fastening bit attached to a spindle in the screw fastening direction or the screw loosening direction, whereby a screw is fastened or loosened. In the case of this screw fastening tool, there has been proposed a construction in which the motor is rotated at low speed at the early stage of the screw fastening to cause the screw to be securely engaged with a workpiece for screw fastening; thereafter, the motor is rotated at high speed so that the screw fastening can be completed quickly, thus allowing a speed change according to the amount by which the switch lever is pulled. 
         [0003]    Japanese Laid-Open Patent Publication No. 2-262953, which relates to an electric grinder, discloses a technique in which, on the assumption that the rotational speed of an electric motor mounted within the tool main body may fluctuate during the actual operation depending on how the operator applies his force to the tool, etc., the fluctuating output rotational speed is displayed on an LED, and the voltage applied to the electric motor is controlled, whereby the output rotational speed of the electric motor is maintained at a previously set output rotational speed. 
         [0004]    However, unlike the grinder mentioned above, a rotary tool such as a screw fastening tool is endowed with a function by which the speed of an electric motor is arbitrarily changed according to the amount by which the user pulls a switch lever. 
         [0005]    In such a lever operation, it is possible to adjust the rotational speed of the motor according to the amount by which the switch lever is pulled; however, it is impossible to comprehend the amount by which the switch lever has been operated. Therefore, when the user intuitively comprehends that the rotating amount is rather insufficient, it can happen that he puts an unnecessarily large force into his fingertip in an attempt to further pull the switch lever despite the fact that the switch lever has been pulled as far as it can go. 
         [0006]    In particular, in the case where the pressing force due to the pulling of the switch lever is detected not by a slide resistance type speed change switch but by a force sensor (load sensor), and where the starting of the electric motor is stopped or a speed change is effected based on an output signal from the sensor, it is possible to minimize the amount by which the switch lever is pulled. In this way, it is possible to mitigate the fatigue of the fingertip of the user in the case of repeated operation. On the other hand, since the amount by which the switch lever is pulled is minimized, it is still difficult to comprehend the amount by which the lever has been pulled. 
         [0007]    Therefore, there has been a need in the art for an electric tool such as a screw fastening tool in which a speed change is effected according to the operation amount of the switch, with the speed change being effected via a switch lever or the like, wherein the user is enabled to comprehend the magnitude by which the switch is being operated. 
       SUMMARY OF THE INVENTION 
       [0008]    An electric tool may include an electric motor, a switch operable by a user for adjusting the rotational speed of the electric motor, an operation amount detection device configured to detect the operation amount of the switch, and an operation amount indicating device coupled to the operation amount detection device and configured to indicate the detected operation amount to the user. 
         [0009]    According to a first embodiment, an electric tool may have an electric motor mounted within a tool main body as a drive source and equipped with a switch for adjusting the rotational speed of the electric motor. The rotational speed of the electric motor may be adjusted according to the operation amount of the switch. The electric tool may include an operation amount detection device for detecting the operation amount of the switch, and an operation amount indicating device for indicating the operation amount of the switch detected by the operation amount detection device. 
         [0010]    In this way, the operation amount of the switch is indicated by the operation amount indicating device, and therefore, user can intuitively comprehend the output rotational speed of the electric motor. The above arrangement is greatly advantageous in that it is possible to intuitively comprehend the rotational speed of the electric motor for a minute operation amount of the switch. This can be accomplished in a construction in which the pressing force produced through the operation of the switch is detected, for example, by a force sensor (load sensor), and the speed of the electric motor is changed based on an output signal from the force sensor. 
         [0011]    In addition to tools such as a screw fastener or a drilling tool, which have rotating output shafts, embodiments of the above arrangement are also applicable to a reciprocating tool, etc., including a reciprocating saw and a jig saw. 
         [0012]    The above arrangement is applicable to a construction in which an electric motor is changed in speed according to the operation amount of a switch lever used for starting and stopping. In addition, it is also possible to provide a switch for adjusting (changing) the rotational speed of an electric motor separately from the switch for starting and stopping the electric motor. Thus, it is applicable to various types of switches that are pulled, pushed or slid for operation, as a speed change switch. 
         [0013]    An output shaft may be rotated by the electric motor as a drive source. Starting and stopping of the electric motor may be effected through a pulling operation of a switch lever by the user. The rotational speed of the electric motor can be adjusted according to the amount by which the switch lever is pulled. The amount by which the switch lever is pulled may be detected by the operation amount detection device and is indicated by the operation amount indicating device. 
         [0014]    With this arrangement, the amount by which the switch lever is pulled is indicated by the operation amount indicating device, whereby the user is enabled to intuitively comprehend the rotational speed level (which is low-speed range, medium-speed range, or high-speed range) of the output shaft. This arrangement is greatly advantageous in that it is possible to intuitively comprehend the level of the output rotational speed of the electric motor for a minute operation amount of the switch lever. This can be accomplished using a construction in which the pressing force produced through the pulling operation of the switch lever is detected, for example, by a force sensor (load sensor), and the electric motor is started, stopped or changed in speed based on an output signal from the force sensor. By applying the above arrangement also to the construction in which a slide resistance type speed change switch is used as the operation amount detecting device instead of the force sensor, the user can intuitively comprehend the output rotational speed of the electric motor through the reported operation amount of the switch lever. 
         [0015]    A force sensor may be used as the operation amount detection means. 
         [0016]    With this arrangement, a pressing force produced, for example, by the pulling operation of the switch lever by the user (the operation of a speed change switch) is detected by the force sensor, and the electric motor is started based on the output signal from this force sensor. Further, the output signal from the force sensor is changed according to a change in the pressing force. The change in pressing force is caused by a change in the amount by which the switch lever is pulled (the operation amount of the speed change switch). This results in a change in the speed of the electric motor. By using the force sensor as the operation amount detection means, it is possible to reduce the amount by which the switch lever is pulled as compared with the conventional construction in which a slide resistance type speed change switch is used. In this way, it is possible to mitigate fatigue in the finger of the user caused by repeated pulling of the switch lever. 
         [0017]    Light-emitting diodes may be used as the operation amount indicating means. 
         [0018]    With this arrangement, three of, for example, five light-emitting diodes may be lit to enable the user to intuitively comprehend, for example, that the pulling amount of the switch lever corresponds, for example, to the medium speed range of the rotational speed level of the output shaft. In addition, it is possible to enable to intuitively comprehend that illumination of one light-emitting diode indicates the pulling amount corresponds to the low-speed range, and illumination of the five light-emitting diodes indicates the pulling amount corresponding to the high-speed range. 
         [0019]    The operation amount indicating device may be provided on a back surface of the tool main body, which is easily visible by the user during use. 
         [0020]    With this arrangement, the user can intuitively and easily comprehend, for example, the amount by which the switch lever is pulled (the operation amount of the speed change switch). 
         [0021]    The operation amount indicating device may report to correspond to both normal and reverse rotations of the electric motor. 
         [0022]    With this arrangement, in a screw fastening machine as the electric tool, it is possible, for example, to intuitively comprehend the switch lever pulling amount (the operation amount of the speed change switch) for both during screw fastening and screw loosening. 
         [0023]    The operation amount indicating device may be capable of indicating in two or more kinds of ways, and a changeover switch may be provided for switching the way of indicating. 
         [0024]    In this way, it is possible to select the indicating method according to the type of work or according to the user&#39;s preference. In this way, it is possible to further improve the operability of the rotary tool. Examples of indicating methods may include a way in which there are provided a plurality of light-emitting diodes which are lit in a number corresponding, for example: (1) to the switch lever pulling amount (the operation amount of the speed change switch), (2) a way in which the absolute value of the rotational speed of the electric motor or the spindle is displayed in value on a liquid crystal panel, (3) a way in which the rotational speed of the electric motor or the spindle is displayed in a meter, and (4) a way in which an indicating sound is produced that changes in frequency or the number of times according to the rotational speed of the electric motor or the spindle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    [ FIG. 1 ]  FIG. 1  is an overall perspective view of a rotary tool according to an embodiment of the present invention. 
           [0026]    [ FIG. 2 ]  FIG. 2  is a vertical sectional view of an operation switch. This figure illustrates an OFF state in which a switch lever has not been pulled. 
           [0027]    [ FIG. 3 ]  FIG. 3  is a vertical sectional view of the operation switch. This figure illustrates an ON state in which a switch lever has been pulled. 
           [0028]    [ FIG. 4 ]  FIG. 4  is a block diagram of a control circuit. 
           [0029]    [ FIG. 5 ]  FIG. 5  is a rear view of the rotary tool as seen from the direction indicated by arrow (V) in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    Next, an embodiment of the present invention will be described with reference to  FIGS. 1 through 5 .  FIG. 1  shows a rotary tool  1  according to the present embodiment. In the present embodiment, a rotary impact type screw fastening tool called an impact driver is exemplified as the rotary tool  1 . This rotary tool  1  is equipped with a tool main body  2  and a handle portion  3 . An electric motor  4 , used as the drive source, and an impact mechanism  6  are mounted within the tool main body  2 . A spindle  5  protrudes from the front portion of the tool main body  2 . At the leading end of the spindle  5 , there is provided a bit holder  5   a  for attaching a drill bit (not shown). When the electric motor  4  is started, rotational power may be output in the screw fastening direction or in the screw loosening direction via the spindle  5 . When an external torque of a level not lower than a fixed level is applied to the spindle  5 , an impact (impact) in the rotational direction is imparted to the spindle  5  by the impact mechanism  6 , making it possible to firmly fasten a screw or to loosen the same. The handle portion  3  is provided so as to protrude downwardly from the lower surface of the tool main body  2 . A rechargeable battery pack  7  is attached to the lower portion of the handle portion  3 . This battery pack  7  can be detached and recharged by a separately prepared charger for repeated use. Using the battery pack  7  as the power source, the electric motor  4  is started, and the electric power is supplied to other electrical components such as an operation amount information supply means  30  that will be later. 
         [0031]    An operation switch  10  configured to be pulled by the user with a finger is provided on the lower surface side of the tool main body  2 . More specifically, it is located on the front surface near the base portion (upper portion) of the handle portion  3 . When the user pulls the operation switch  10  with a fingertip of his hand grasping the hand portion  3 , the electric motor  4  is started; when the pulling operation is released, the electric motor  4  is stopped. As the pulling amount of the operation switch  10  increases, the speed of the electric motor  4  is increased, and as the pulling amount decreases, the speed of the electric motor  4  is reduced. The rotary tool  1  according to the present embodiment is characterized in that a relatively weak pulling can generate a sufficient operable amount with respect to the operation switch  10 , and that it is possible for the user to visually and intuitively comprehend the pulling amount.  FIGS. 2 and 3  illustrate the operation switch  10  in detail. 
         [0032]    The operation switch  10  is equipped with a trigger type switch lever  11 , and a switch main body  12  to be operated through the pulling operation of the switch lever  11 . The switch main body  12  is mounted within the upper portion of the handle portion  3 . The switch lever  11  is supported by a case  17  of the switch main body  12  via a support rod portion  11   a  so as to be capable of a translation movement. The support rod portion  11   a  of the switch lever  11  is inserted into the case  17 . Inside the case  17 , an operation block  13  is attached to the leading end of the support rod portion  11   a . The operation block  13  moves in unison with the switch lever  11  via the support rod portion  11   a . This operation block  13  is urged in such a direction that the switch lever  11  returns toward the OFF side (front side), by a first compression spring  14  provided between itself and a rear wall  17   a  of the case  17 . In this way, the switch lever  11  is operated to be pulled against the urging force of the first compression spring  14 . 
         [0033]    An operation pin  15  is supported by the operation block  13  so as to be movable in the forward and rearward direction. The operation pin  15  protrudes from the rear surface of the operation block  13 . The operation pin  15  is urged by a second compression spring  16  in such a direction such that the operation pin  15  will protrude from the rear surface of the operation block  13 . A force sensor  20  is mounted to the rear wall  17   a  of the case  17  at a position rearward of the operation pin  15 . This force sensor  20  is a load sensor configured to transform a change in the pressing force of the operation pin  15  to a change in a resistance ratio of a bridge circuit before outputting it; in the present embodiment, a conventionally known force sensor is used. Based on a voltage signal output from this force sensor  20 , the supply voltage to the electric motor  4  is changed, whereby the electric motor  4  is started, stopped, and changed in speed. 
         [0034]    Thus, when the user pulls the switch lever  11  with a finger tip of his hand grasping the handle portion  3 , the operation block  13  retreats in unison with the switch lever, and the operation pin  15  protruding from the rear surface is caused to abut the force sensor  20 . When the operation pin  15  is caused to abut the force sensor  20 , a pressing force is generated against the force sensor  20 . The operation pin  15  generates the pressing force when it is brought to abut the force sensor  20  through a relatively weak pulling of the switch lever  11 . When the pressing force is generated against the force sensor  20 , the resultant change in the resistance ratio of the bridge circuit is output as an electric signal, whereby the electric motor  4  is started. 
         [0035]    As the operation block  13  retreats by further pulling the switch lever  11 , the operation pin  15  advances with respect to the operation block  13  against the force of the second compression spring  16 , with the result that the urging force of the second compression spring  16  acting on the operation pin  15  gradually increases. In this way, the pressing force of the operation pin  15  against the force sensor  20  is gradually increased. 
         [0036]    As the pressing force of the operation pin  15  against the force sensor  20  is gradually increased, the electric signal of the force sensor  20  undergoes a change, and the speed of the electric motor  3  is increased. Conversely, as the pulling operation on the switch lever  11  is restored by the urging force of the first compression spring  14 , the operation block  13  is restored forward in unison with the switch lever, so that the pressing force of the operation pin  15  against the force sensor  20  is reduced, resulting in a reduction in the speed of the electric motor  3 . 
         [0037]    In this way, through a change in the amount by which the switch lever  11  is pulled, the pressing force against the force sensor  20  undergoes a change, whereby the electric motor  3  undergoes a change in speed based on a change in the resultant output voltage signal, and, at the same time, based on the change in the voltage signal, the change in the pulling operation amount of the switch lever  11  is visually reported to the user by the operation amount information supply means  30 . As a result, the force sensor  20  functions as the operation amount detection means for detecting the pulling operation amount of the switch lever  11 . 
         [0038]    As shown in  FIG. 4 , the voltage signal of the force sensor  20 , which is changed through the operation of pulling the operation switch  10 , is input to a control circuit C 0 . At the control circuit C 0 , a PWM control is performed based on the voltage signal of the force sensor  20 , and the result thereof is output to a drive circuit C 1  of the electric motor  4  and to the operation amount information supply means  30 . The electric power determined through the PWM control at the control circuit C 0  is supplied from a DC power source (the battery pack  7 ) to the electric motor  4  via the drive circuit C 1 , so that the electric motor  4  is rotated at a predetermined rotational speed. 
         [0039]    In the present embodiment, a plurality of light-emitting diodes (LEDs  31 ) are used as the operation amount information supply means  30 . As shown in  FIG. 5 , a total of  10  LEDs  31  are arranged at positions which are on the rear surface of the tool main body  2  and which can be easily visually observed by the user. As shown in the drawing, the ten LEDs  31  are left and right symmetrically arranged along a same circular circumference to correspond to the shape of the rear surface of the tool main body  2 . The voltage signal of the force sensor  20 , which is changed according to the pulling operation amount of the operation switch  10 , is interpreted by the control circuit C 0 , and an appropriate number of LEDs  31  are lit based on the interpreted result. By visually checking the number of LEDs  31  that are lit, it is possible for the user to intuitively comprehend the pulling operation amount of the switch lever  11  and, eventually, the level (low-speed, medium-speed, high-speed) of the output rotational speed of the electric motor  4 . 
         [0040]    In the case of the present embodiment, the ten LEDs  31  are arranged with five on each side of the right and left half circular circumferences. For example, in the low-speed range, where the pulling operation amount of the switch lever  11  is small, the uppermost two right and left LEDs  31  are lit; and as the pulling operation amount is gradually increased to attain higher speed, the lower two right and left LEDs are lit, and then, the still lower two and left LEDs are lit, making it possible for the user to visually and intuitively comprehend that the electric motor  3  is being rotated in the medium-speed range. 
         [0041]    When the operation switch  10  is pulled to the stroke end, where the maximum pressing force acts on the force sensor  20 , this is interpreted by the control circuit C 0  to cause all the ten LEDs  31  to be lit. This is visually checked by the user, thus making it possible for the user to visually and intuitively comprehend that the pulling operation amount of the switch lever  11  is at its maximum, and the electric motor  3  is being rotated at the maximum speed. In the state in which the switch lever  11  is pulled to the stroke end to cause the electric motor  3  to be rotated at the maximum speed, the spindle  5  rotates at the maximum speed, and, at the same time, it is possible to obtain a large striking force by the impact mechanism  6 , whereby it is possible to quickly perform screw fastening or screw loosening. 
         [0042]    On the lower surface side of the tool main body  2  and at the base portion (upper portion) of the handle portion  3 , there is provided a normal/reverse switching rod  8  for switching the rotational direction of the electric motor  3 . This normal/reverse switching rod  8  consists of a single bar, which is arranged so as to extend in the left and right directions through a portion near the base portion of the handle portion  3 . By pushing this normal/reverse switching rod  8  to the left or to the right, it is possible to effect normal/reverse switching of the rotational direction of the electric motor  3 , whereby it is possible to perform screw fastening or screw loosening. 
         [0043]    With the rotary tool  1  according to the present embodiment constructed as described above, the electric motor  3  is started by pressing the operation pin  15  against the force sensor  20  through the pulling operation of the switch lever  11  of the operation switch  10 , and, further, the pulling operation amount of the switch lever  11  is changed, so that the pressing force against the force sensor  20  is changed to effect a speed change in the electric motor  3 . Therefore, as compared to the case of the conventional slide resistance type speed change switch, it is possible to substantially reduce the pulling operation amount of the switch lever  11 , whereby it is possible to mitigate the fatigue of the fingertip of the user as a result of repeated pulling operation. 
         [0044]    Further, while effecting a speed change in the electric motor  3  through the detection of the pulling operation amount of the switch lever  11  by the force sensor  20  as the operation amount detection means, it is possible for the user to visually and intuitively comprehend the pulling operation amount (the output rotational speed level of the electric motor  3  or of the spindle  5 ) based on the number of LEDs  31  that are lit to serve as the indicating means  30 , so that it is possible to improve the operability of the rotary tool  1 . 
         [0045]    The above-described embodiment allows various modifications. For example, while in the above-described example a total of ten LEDs  31  are employed as the indicating means  30 , it is also possible to provide a total of three LEDs  31  in correspondence with the low-speed range, medium-speed range, and high-speed range. It is also possible to arrange more than ten LEDs to provide a finer display of the pulling operation amount. In short, the electric motor  3  is started, stopped, and changed in speed based on a change in the pressing force against the force sensor by the pulling operation on the switch lever  11 , and, at the same time, the pulling operation amount of the switch lever  11  is made known to the user by the operation amount indicating means, whereby it is possible to improve the operability and usability of the rotary tool  1 . 
         [0046]    Other than the above-described construction in which a plurality of LEDs  31  are lit, the operation amount indicating means may have a construction in which a liquid crystal panel is provided on the rear surface of the tool main body  2  to display the values of the pulling operation amount of the switch lever  11  in percentage, or a construction which produces an indicating sound that changes in scale or in the number of times of production according to the pulling operation amount of the switch lever  11 . It is also possible that a changeover switch can switch for display between these plural ways of indicating. Further, as the operation amount indicating means, it is also possible to arrange a meter equipped with an indicator on the rear surface of the tool main body  2 . 
         [0047]    While in the above-described example the force sensor  20  is exemplified as the operation amount detection means, the same effect can be achieved by applying the above operation amount indicating means to the construction which uses a slide resistance type speed change switch as the operation amount detection means. 
         [0048]    Further, the pulling operation amount of the switch lever  11  (the operation amount of the switch) may include applying a voltage command value of the electric motor  3  (the duty of the PWM control, etc.) which corresponds to the pulling operation amount. 
         [0049]    Further, while in the above-described electric tool the speed change of the electric motor  3  is effected through the pulling operation on the switch lever  11 , the above-described operation amount detection means and the operation amount indicating means are also applicable to the operation amount of an electric tool in which the speed change is effected through the operation of depressing a pushbutton or the operation of sliding a slider. 
         [0050]    Further, while in the above-described example a screw fastening tool (rotary tool) has been exemplified as the electric tool, similar operation amount detection means and similar operation amount indicating means are also applicable to a reciprocating tool such as a reciprocating saw or a jig saw.