Patent Publication Number: US-10770245-B2

Title: Contact structure for switch, trigger switch and electric power tool

Description:
TECHNICAL FIELD 
     The present invention relates to a switch contact structure, a trigger switch, and an electric power tool. 
     BACKGROUND ART 
     According to an increase in output of an electric power tool, the level of vibration of the tool has been increased. A contact force of a switch is therefore more necessary than before. As a conventional technique for increasing a contact force, for example, a trigger switch disclosed in Patent Literature 1 is known. The term “contact force” means a force by which a contact of a switch is pressed against the other contact. 
     As illustrated in (a) of  FIG. 10 , a trigger switch  100  disclosed in Patent Literature 1 includes (i) a first movable contact  111  which is provided at one end part and (ii) a second movable contact  112  which is provided at the other end part. The trigger switch  100  further includes (i) a movable contact piece  110  configured to turn while being supported at the support member  101 , (ii) a slide member  102  configured to slide while pressing a slide surface  113  of the movable contact piece  110  so that the slide member  102  causes the movable contact piece  110  to turn in a seesaw-like pattern, (iii) a first terminal  103  having a first fixed contact  103   a , (iv) a second terminal  104  having a second fixed terminal  104   a , and (v) a plunger  106  configured to cause the slide member  102  to move horizontally. 
     As illustrated in (b) of  FIG. 10 , in a case where the trigger switch  100  thus configured pushes the plunger  106  in, the slide member  102  slides in a rightward direction on the slide surface  113 . When the slide member  102  passes a protruding support point  113   a  provided on the slide surface  113 , the movable contact piece  110  turns so that the second movable contact  112  comes into contact with the second fixed terminal  104   a.    
     As illustrated in (c) of  FIG. 10 , in a case where the plunger  106  is further pushed in, the slide member  102  further slides in the rightward direction on the slide surface  113 . Then, in a case where the slide member  102  reaches a top portion  113   b  of the slide surface  113  at the movable contact piece  110 , the pressing force of the slide member  102  increases. This causes the second movable contact  112  and the second fixed terminal  104   a  to be firmly in contact with each other. 
     According to the trigger switch  100  thus configured, the contact force between the second movable contact  112  and the second fixed terminal  104   a  can be increased so as to improve a vibration resistance. 
     CITATION LIST 
     Patent Literature 
     [Patent Literature 1] 
     Japanese Patent Application Publication, Tokukai, No. 2015-99645 (Publication Date: May 28, 2015) 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, since a seesaw contact is used according to the conventional trigger switch  100 , tactile feedback occurs in the process of operation. The seesaw contact is therefore not suitable for a speed-change switch which is configured so that an output of a target of driving increases in response to a retraction amount of a trigger. Therefore, in order to remove tactile feedback in a seesaw contact method, it is necessary to, for example, add another component. 
     Furthermore, although a large contact force can be achieved with the conventional trigger switch  100 , the pressure of the plunger  106  accordingly becomes large and the resistance to the sliding becomes large. This unfortunately causes the operating load to become large or leads to a deterioration of operational feeling. 
     An object of an aspect of the present invention is to provide a switch contact structure, a trigger switch, and an electric power tool, each of which can increase a contact force so as to improve a vibration resistance. 
     Solution to Problem 
     A switch contact structure in accordance with an aspect of the present invention includes: an operation section; a first movable contact member; and a first counter contact member configured to face the first movable contact member, in a case where an amount of movement of the operation section reaches a first movement amount, the first movable contact member coming into contact with the first counter contact member due to a spring force applied to the first movable contact member, and in a case where the amount of movement of the operation section reaches a second movement amount which is larger than the first movement amount, the operation section pressing the first movable contact member against the first counter contact member. 
     A trigger switch in accordance with an aspect of the present invention can be configured to include: the contact structure in accordance with the aspect of the present invention, the operation section being configured to move in coordination with a trigger operated by a user. 
     An electric power tool in accordance with an aspect of the present invention can be configured to include the trigger switch in accordance with the aspect of the present invention. 
     Advantageous Effects of Invention 
     With an aspect of the present invention, it is possible to increase a contact force so as to improve a vibration resistance. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a left side view illustrating an embodiment of a trigger switch of the present invention and showing that a plunger is pressing down a flat spring of a second switch while respective contacts of a first switch and of the second switch of the trigger switch are both closed. 
         FIG. 2  is a perspective view illustrating a configuration of the trigger switch. 
         FIG. 3  is a left side view illustrating the configuration of the trigger switch and showing that respective contacts of the first switch and of the second switch are both opened. 
         FIG. 4  is an exploded perspective view illustrating the configuration of the trigger switch. 
         FIG. 5  is a perspective view which illustrates the configuration and main components of the trigger switch and in which it is viewed from a right surface side that respective contacts of the first switch and of the second switch are both opened. 
         FIG. 6  is a perspective view illustrating the configuration of the second switch having a flat spring of the trigger switch. 
         FIG. 7  is a left side view illustrating the configuration of the trigger switch and showing that the contact of the first switch and the contact of the second switch are closed and opened, respectively. 
         FIG. 8  is a left side view illustrating the configuration of the trigger switch and showing that the contact of the first switch and the contact of the second switch are both closed. 
         FIG. 9  is a graph showing the following relationships in the trigger switch: (i) a relationship between (a) a retraction amount of the trigger of the trigger switch and (b) respective contact forces of the first switch and of the second switch and (ii) a relationship between (a) the retraction amount of the trigger and (b) an output. 
       (a) of  FIG. 10  is a left side cross-sectional view which illustrates a configuration of a conventional trigger switch having a seesaw contact and which shows that a contact of the trigger switch is opened. (b) of  FIG. 10  is a left side cross-sectional view showing that the contact of the trigger switch is closed. (c) of  FIG. 10  is a left side cross-sectional view showing that the contact force is increased while the contact is closed. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following description will discuss an embodiment of the present invention with reference to  FIGS. 1 through 9 . In the following description, a trigger switch provided in an electric power tool will be described. The electric power tool includes the trigger switch. The trigger switch in accordance with the present embodiment is to be used for an electric power tool such as an impact wrench. 
       FIG. 2  is a perspective view illustrating a configuration of a trigger switch  1  in accordance with the present embodiment.  FIG. 3  is a left side view illustrating the configuration of the trigger switch  1  and showing that respective contacts of a first switch and of a second switch are both opened.  FIG. 4  is an exploded perspective view illustrating the configuration of the trigger switch  1 . 
     As illustrated in  FIG. 2 , the trigger switch  1  in accordance with the present embodiment includes (i) a housing  2  formed by causing a left-side cover  2   a  and a right-side cover  2   b , which are box-shaped, to face each other and (ii) a trigger  3  provided so as to protrude toward a front surface from the housing  2  and to retract toward the housing  2 . Above the housing  2 , a switching lever  4  is provided. In the present embodiment, a side of the trigger switch  1 , on which side the trigger  3  is provided, is a front side. 
     The switching lever  4  is configured to lock, while the trigger  3  is not operated, an extending movement of the trigger  3  by causing a tip part of the switching lever  4  to come into contact with a center protrusion  3   a  which is provided above the trigger  3 . Meanwhile, in a case where the switching lever  4  is slightly turned clockwise or counterclockwise, the tip part of the switching lever  4  loosely fits into a loose-fitting recess  3   c  which is provided between the center protrusion  3   a  and a side surface wall  3   b  above the trigger  3 . This allows the trigger  3  to extend toward the housing  2 . 
     As illustrated in  FIGS. 3 and 4 , the trigger  3  is provided in front of an upper part of the housing  2  and includes an operation shaft  3   d  which extends from the trigger  3  toward the housing  2 . The operation shaft  3   d  is covered with an accordion-like cylindrical body  3   e.    
     Inside the housing  2 , the following are contained: (i) a base  10  configured to combine members together, (ii) a plunger  6  serving as a slide member, (iii) a switch opening-closing mechanism  7  serving as an opening-closing mechanism, (iv) a printed circuit board  8 , and (v) the like. 
     As illustrated in  FIG. 4 , the base  10  has a shape made by cutting out one side surface from a box-like shape, and includes a positioning recess  11  which is provided at an upper front part of the base  10  and which is configured to position the switching lever  4 . Below the base  10 , the following are juxtaposed: (i) a positioning pin  12  configured to attach a second coil spring  32  (described later) and (ii) a mount  13  configured to restrict the position of the second movable piece  31 . 
     As illustrated in  FIG. 4 , the plunger  6  has (i) a shape which allows the plunger  6  to slide in front and rear directions in the base  10 , (ii) a through-hole  6   a  which passes through the plunger  6  in the front and rear directions, and (iii) a pair of guide grooves  6   b  and  6   b  on a left side surface of the plunger  6 . Into the through-hole  6   a , a resetting coil spring  3   f , which is configured to cause the retracting trigger  3  to return, is to be inserted. Into the pair of guide grooves  6   b  and  6   b , corresponding sliders  6   c  and  6   c  are fixed with a pressure. This allows the plunger  6  to (i) move backward in the base  10  in response to the trigger  3  retracting and (ii) return forward, by the return force of the resetting coil spring  3   f , in response to the trigger  3  returning forward. 
     As illustrated in  FIG. 3 , from a bottom surface of the plunger  6 , sliding parts  6   d  and  6   e  having respective taper surfaces protrude. The sliding part  6   d  is configured to slide the second movable piece  31  of the second switch  30 . The sliding part  6   e  is configured to slide a first movable piece  21  of the first switch  20 . The sliding part  6   d  extends longer than the sliding part  6   e  in the front and rear directions. As illustrated in  FIG. 5  described later, the sliding part  6   e  extends shorter than the sliding part  6   d  in the front and rear directions. The plunger  6  and the sliding parts  6   d  and  6   e  constitute an operation section configured to move in coordination with the trigger  3  which is operated by a user. 
     As illustrated in  FIG. 4 , the printed circuit board  8  has a shape so as to be able to cover an opening of the base  10 . The printed circuit board  8  has an inner-facing surface on which (i) a slide resistive element (not shown) is printed and (ii) a microcomputer is mounted. To a lower end part of the printed circuit board  8 , a socket  8   a  is attached. 
     The printed circuit board  8  can be integrated with the base  10  by being fitted into and thus combined with the base  10  in which the plunger  6  is contained. In a case where the plunger  6  moves forward or backward, the pair of sliders  6   c  and  6   c  attached to the plunger  6  slide along the slide resistive element (not shown) of the printed circuit board  8 . This allows a resistance of the slide resistive element to be changed, and therefore allows the trigger switch  1  to supply, to an electric power tool, an output which corresponds to the movement amount of the plunger  6 , and ultimately corresponds to the retraction amount of the trigger  3 . 
     The trigger  3  includes the operation shaft  3   d  which protrudes forward. One end part of the accordion-like cylindrical body  3   e  inserted into the operation shaft  3   d  is prevented from coming off by a ring  3   g . The trigger  3  can be integrated with the plunger  6  by engaging, through sliding, a tip part of the operation shaft  3   d  with an engagement hole (not shown) of the plunger  6 , the tip part being protruding from the accordion-like cylindrical body  3   e.    
     The switching lever  4  can reverse the direction of rotation of a motor (not shown) by being turned with the turning shaft part  4   a  serving as a fulcrum. 
     According to the trigger switch  1  of the present embodiment, the switch opening-closing mechanism  7  (switch contact structure) includes the first switch  20  and the second switch  30 . 
       FIG. 5  is a perspective view which illustrates the configuration and main components of the trigger switch  1  and in which it is viewed from a right surface side that respective contacts of the first switch  20  and of the second switch  30  are both opened.  FIG. 6  is a perspective view illustrating the configuration of the second switch  30  having a flat spring of the trigger switch  1 . The configurations of the first switch  20  and of the second switch  30  according to the present embodiment will be described below with reference to  FIGS. 5 and 6 . 
     As illustrated in  FIG. 5 , the first switch  20  includes (i) the first movable piece  21  (second movable contact member), (ii) a first movable contact  21   a  serving as a first opening-closing terminal provided at one end part of the first movable piece  21 , (iii) a first fixed contact  21   b  (second counter contact member) serving as a first fixed terminal provided so as to face the first movable contact  21   a , (iv) a first inhibiting part  21   c  provided at the other end part of the first movable piece  21  (opposite the one end part at which the first movable contact  21   a  is provided), and (v) a first coil spring  22  configured to elastically cause the first movable piece  21  to be in a closed state. 
     The second switch  30  includes (i) the second movable piece  31  (first movable contact member), (ii) a second movable contact  31   a  serving as a second opening-closing terminal provided at one end part of the second movable piece  31 , (iii) a second fixed contact  31   b  (first counter contact member) serving as a second fixed terminal provided so as to face the second movable contact  31   a , (iv) a second inhibiting part  31   c  provided at the other end part of the second movable piece  31  (opposite the one end part at which the second movable contact  31   a  is provided), and (v) a second coil spring  32  configured to elastically cause the second movable piece  31  to be in a closed state. 
     Note that the first movable contact  21   a  is configured by a silver (Ag) contact so that it is easy to stop arc discharge which occurs during an opening motion. Note, however, that a surface of the silver (Ag) contact is easily made rough by arc discharge. This causes a contact resistance to be large, and consequently causes stable contact to be difficult. According to the present embodiment, therefore, the first movable contact  21   a  opens and closes with timings different from those of the second movable contact  31   a , so that arc discharge is prevented from occurring at one of the contacts. This increases a contact force at the second movable contact  31   a  in which a constantly-clean contact. Note, however, that because an increase in contact force stabilizes the contact, any one of the first movable contact  21   a  and the second movable contact  31   a  can be configured by a silver (Ag) contact. The term “contact force” means a force by which a contact of a switch is pressed against the other contact. 
     As illustrated in  FIG. 5 , (i) the first movable contact  21   a  is electrically connected to a negative electrode-side terminal  41  via the first movable piece  21  and (ii) the second movable contact  31   a  is electrically connected to the negative electrode-side terminal  41  via the second movable piece  31 . Meanwhile, (i) the first movable contact  21   a  is electrically connected to a positive electrode-side terminal  42  via the first fixed contact  21   b  and (ii) the second movable contact  31   a  is electrically connected to the positive electrode-side terminal  42  via the second fixed contact  31   b . The first fixed contact  21   b  and the second fixed contact  31   b  are electrically connected to each other. The first switch  20  and the second switch  30  are therefore connected in parallel. According to this configuration, even in a case where a vibration is applied to the trigger switch  1  while the trigger switch  1  is turned on (closed), the trigger switch  1  remains turned on so as to prevent the occurrence of arc discharge, unless the first switch  20  and the second switch  30  are both simultaneously opened. This allows for an increase in vibration resistance. 
     According to the present embodiment, in particular, the trigger switch  1  includes a flat spring  33  which is inserted into two attachment recesses  31   d  and  31   d  on an upper side of the second movable piece  31  of the second switch  30  (see  FIG. 6 ). Note that the flat spring  33  has a curved shape while being unpressed. According to the trigger switch  1  of the present embodiment, the sliding part  6   d  of the plunger  6  slides on an upper surface of the flat spring  33  so as to press down the flat spring  33 . Ultimately, the sliding part  6   d  elastically causes the second movable piece  31  to be in a closed state. This causes the second movable contact  31   a  to be pressed against the second fixed contact  31   b . Consequently, a contact force between the second movable contact  31   a  and the second fixed contact  31   b  is increased. According to the present embodiment, the elastic member (flat spring  33 ) is made of, for example, steel so that the second movable piece  31  is elastically caused to be in a closed state. However, the material for the elastic member is not necessarily limited as such. Alternatively, for example, the elastic member can be made of a rubber or the like instead of the flat spring  33 . 
     According to the present embodiment, the flat spring  33 , which is an elastic body, is attached to the second movable piece  31  which is a rigid body. However, the present invention is not necessarily limited as such. Alternatively, for example, a curved member, which is a rigid body, can be attached to a second movable piece  31  which is made of an elastic member. The curved member has, for example, a shape similar to that of the flat spring  33 . According to this configuration also, the second movable piece  31 , which is an elastic body, is elastically deformed by causing the sliding part  6   d  of the plunger  6  to press the curved member which is a rigid body. This makes it possible to elastically press the second movable contact  31   a  against the second fixed contact  31   b.    
       FIG. 7  is a left side view illustrating an internal configuration of the trigger switch  1  and showing that the contact of the first switch  20  and the contact of the second switch  30  are closed and opened, respectively.  FIG. 8  is a left side view illustrating the internal configuration of the trigger switch  1  and showing that the contact of the first switch  20  and the contact of the first switch  20  are both closed.  FIG. 1  is a left side view showing that the sliding part  6   d  of the plunger  6  is pressing down the flat spring  33  of the second switch  30  while the respective contacts of the first switch  20  and of the second switch  30  of the trigger switch  1  are both closed. The operation of the trigger switch thus configured will be described below with reference to  FIGS. 2, 3, 7, 8, and 1 . 
     As illustrated in  FIG. 2 , while the switching lever  4  is present in a neutral position of the trigger switch  1 , the tip part of the switching lever  4  is in contact with the center protrusion  3   a  of the trigger  3 . This prevents the trigger  3  from retracting, and therefore presents an operation error. 
     In so doing, as illustrated in  FIG. 3 , the respective contacts of the first switch  20  and of the second switch  30  are both opened inside the housing  2 . 
     In this state, turning the switching lever  4  counterclockwise with the turning shaft part  4   a  serving as a fulcrum allows the tip part of the switching lever  4  to loosely fit into the loose-fitting recess  3   c  located between one side surface wall  3   b  and the center protrusion  3   a  of the trigger  3 . This allows the trigger  3  to be retractable into the housing  2 . Note that immediately before the trigger  3  retracts, the sliders  6   c  and  6   c  come into contact, at a maximum resistance, with the slide resistive element (not shown) of the printed circuit board  8 . 
     According to the first switch  20 , the first coil spring  22  (compression spring) elastically applies a force to the first movable piece  21 . This causes a clockwise turning force to be applied to the first movable piece  21  in the state illustrated in  FIG. 3 . However, the sliding part  6   e  of the plunger  6 , to which plunger  6  the resetting coil spring  3   f  applies a force, is in contact with the first inhibiting part  21   c  of the first movable piece  21 . This restricts the turning of the first movable piece  21 . Consequently, the first switch  20  is in an opened state while there is a space between the first movable contact  21   a  and the first fixed contact  21   b.    
     Similarly, according to the second switch  30 , the second coil spring  32  (extension spring) elastically applies a force to the second movable piece  31 . This causes a clockwise turning force to be applied to the second movable piece  31  in  FIG. 3 . However, the sliding part  6   d  of the plunger  6 , to which plunger  6  the resetting coil spring  3   f  applies a force, is in contact with the second inhibiting part  31   c  of the second movable piece  31 . This restricts the turning of the second movable piece  31 . Consequently, the second switch  30  is in an opened state while there is a space between the second movable contact  31   a  and the second fixed contact  31   b.    
     In a case where, in this state, a worker causes the trigger  3  to retract, the plunger  6  engaged with the operation shaft  3   d  slides backward (in a direction toward the right side in  FIG. 3 ). Consequently, the sliders  6   c  and  6   c  combined with the plunger  6  slide on the printed circuit board  8 . As a result of the sliding of the sliders  6   c  and  6   c , the resistance gradually becomes small, so that a flow of an electric current increases. This causes an operation lamp or the like (not shown) to be turned on. 
     As illustrated in  FIG. 7 , causing the trigger  3  to further retract causes the sliding part  6   e  of the plunger  6  to be no longer in contact with the first inhibiting part  21   c  of the first switch  20 . This causes the first movable piece  21  to be turned clockwise (in  FIG. 7 ) by the spring force of the first coil spring  22 . This causes the first movable contact  21   a  to come into contact with the first fixed contact  21   b . Consequently, the first movable contact  21   a  is pressed against the first fixed contact  21   b  only by the spring force of the first coil spring  22 . 
     As illustrated in  FIG. 8 , causing the trigger  3  to further retract causes the operation shaft  3   d  to be pushed deeper into the base  10 . This causes the sliding part  6   d  to be no longer in contact with the second inhibiting part  31   c  of the second switch  30 . This causes the second movable piece  31  to be turned clockwise (in  FIG. 8 ) by the spring force of the second coil spring  32 . This causes the second movable contact  31   a  to come into contact with the second fixed contact  31   b . In this stage, the sliding part  6   d  is not in contact with the flat spring  33 , so that the second movable contact  31   a  is pressed against the second fixed contact  31   b  only by the spring force of the second coil spring  32 . 
     Causing the trigger  3  to further retract than is illustrated in  FIG. 8  causes the operation shaft  3   d  to be pushed even deeper into the base  10  as illustrated in  FIG. 1 . This causes the sliding part  6   d  to come into contact with the flat spring  33  provided on the second switch  30 . This causes the sliding part  6   d  to press the flat spring  33  toward the second movable contact  31   a . Due to the elastic force of the flat spring  33 , the second movable contact  31   a  is further pressed against the second fixed contact  31   b . This causes a further increase in contact force between the second movable contact  31   a  and the second fixed contact  31   b . In so doing, the resistance, which changes in accordance with the sliding, becomes minimum, so that a maximum electric current flows through the sliders  6   c  and  6   c . This causes a microcomputer (not shown) to output a signal so as to cause the rotation speed of the motor (target of driving; not shown) to be maximum. 
     According to the trigger switch  1  of the present embodiment, therefore, the contact force of the second switch  30  is increased by the flat spring  33  while the second switch  30  is in a closed state. 
     In this state, in a case where a worker reduces a force which causes the trigger  3  to retract, the plunger  6  is pushed back by the spring force of the resetting coil spring  3   f . This causes the sliders  6   c  and  6   c  to slide in a reverse direction on the printed circuit board  8 . Then, because the sliding part  6   d  causes the second movable piece  31  of the second switch  30  to turn in a reverse direction, the second movable contact  31   a  of the second switch  30  becomes separated from the second fixed contact  31   b . Subsequently, by the force of the sliding part  6   d , the first movable piece  21  turns against the spring force of the first coil spring  22 . This causes the first movable contact  21   a  to become separated from the first fixed contact  21   b.    
     In addition, turning the switching lever  4  clockwise from the neutral position with the turning shaft part  4   a  serving as a center point allows the tip part of the switching lever  4  to loosely fit into the loose-fitting recess  3   c  located between the other side surface wall  3   b  and the center protrusion  3   a  of the trigger  3 . Therefore, causing the trigger  3  to retract as described earlier causes the motor to rotate in the reverse direction. 
       FIG. 9  is a graph showing the following relationships in the trigger switch  1 : (i) a relationship between (a) the retraction amount of the trigger  3  and (b) the respective contact forces of the first switch  20  and of the second switch  30  and (ii) a relationship between (a) the retraction amount of the trigger  3  and (b) an output. The following description will discuss, with reference to  FIG. 9 , (i) the relationship between (a) the respective contact forces of the first switch  20  and of the second switch  30  and (b) the retraction amount of the trigger  3  and (ii) the relationship between (a) the retraction amount of the trigger  3  and (b) the motor output. These relationships are caused by the above-described operation of the trigger switch  1  of the present embodiment. The horizontal axis indicates the retraction amount of the trigger  3 . The left vertical axis indicates the contact force. The right vertical axis indicates the motor output. An increase in motor output leads to, for example, an increase in the rotation speed of the motor of the electric power tool, and consequently leads to an increase in vibration. 
     As illustrated in  FIG. 9 , while the movement amount of the trigger  3  is between a retraction amount of 0 and a first retraction amount L 1 , (i) the first switch  20  and the second switch  30  are each opened, (ii) the contact force of each of the first switch  20  and of the second switch  30  is 0, and (iii) the motor output is 0. 
     After the movement amount of the trigger  3  exceeds the first retraction amount L 1  and until the movement amount reaches a second retraction amount L 2 , (i) the first switch  20  is closed and (ii) the second switch  30  is opened. The first movable contact  21   a  of the first switch  20  is pressed against the first fixed contact  21   b  only by the spring force of the first coil spring  22 . Consequently, the contact force of the first switch  20  is maintained at a contact force P 1 . Note that the motor output (indicated by the oblique solid line in  FIG. 9 ) increases in accordance with an increase in movement amount of the trigger  3 . 
     Subsequently, after the movement amount of the trigger  3  exceeds the second retraction amount L 2  and until the movement amount reaches a third retraction amount L 3 , (i) the first switch  20  remains closed and (ii) the second switch  30  is closed. The second movable contact  31   a  of the second switch  30  is pressed against the first fixed contact  21   b  only by the spring force of the second coil spring  32 . Note that the second movable contact  31   a  is pressed against the second fixed contact  31   b  by a contact force P 2  which is stronger than the contact force P 1  of the first switch  20 . Note also that the first coil spring  22  and the second coil spring  32  are not fixed to the plunger  6  or the sliding part  6   d . The respective spring forces of the first coil spring  22  and of the second coil spring  32  are not applied to the plunger  6  or to the sliding part  6   d . This prevents a user from feeling tactile feedback. 
     After the movement amount of the trigger  3  exceeds the third retraction amount L 3 , the sliding part  6   d  is in contact with the flat spring  33 . This (i) causes the first switch  20  to remain closed with the contact force P 1  and (ii) causes the second switch  30  to remain closed with a contact force P 3  which is stronger than the contact force P 2 . The second movable contact  31   a  of the second switch  30  is pressed against the second fixed contact  31   b  not only by the spring force of the second coil spring  32  but also by a force of the sliding part  6   d  to press against the flat spring  33 . For simplicity,  FIG. 9  shows that the contact force rises up to the contact force P 3  at the third retraction amount L 3 . Note, however, that, the contact force of the second switch  30  may rise gradually after reaching the third retraction amount L 3 . Specifically, in a case where the movement amount of the trigger  3  (movement amount of the sliding part  6   d ) increases further than the third retraction amount L 3 , the contact force may continuously increase from the contact force P 2  to the contact force P 3  in accordance with an increase in movement amount. This is because the flat spring  33  has a surface (curved surface) inclined with respect to the moving direction of the sliding part  6   d  of the plunger  6 , and consequently the sliding part  6   d  comes into contact with the surface of the flat spring  33  thus inclined. Note that the curved surface of the flat spring  33 , into which the sliding part  6   d  comes into contact, is curved so as to protrude. Therefore, while the surface of the flat spring  33 , with which the sliding part  6   d  is in contact, is parallel to the moving direction of the sliding part  6   d  (as illustrated in  FIG. 1 ), the contact force becomes constant. 
     While the motor output is large, the vibration of an electric power tool is also large. It is therefore necessary to increase the contact force of a switch. According to the trigger switch  1 , the contact of the second switch  30  remains closed due to a resultant force of the spring force of the second coil spring  32  and the force of the flat spring  33 . Even in a case where the first switch  20  is temporarily opened due to the vibration, the second switch  30 , to which a stronger contact force is applied, remains closed. This prevents the occurrence of chattering or arc discharge. In addition, the first movable contact  21   a , which has a silver contact that makes it easy to prevent arc discharge during an opening motion, is not pressed against the first fixed contact  21   b  by a force which is stronger than necessary. It is therefore possible to prevent the deformation of the silver contact and consequently improves durability. 
     In addition, since the sliding part  6   d  comes into contact with the flat spring  33  which elastically deforms, it is possible to restrict the tactile feedback when the trigger  3  retracts. Furthermore, in a case where the sliding part  6   d  moves, the sliding part  6   d  comes into contact with the surface of the flat spring  33 , which surface is inclined with respect to the moving direction of the sliding part  6   d . It is therefore possible to further restrict the tactile feedback when the trigger  3  retracts. 
     According to the present embodiment, therefore, it is possible to increase a contact force so as to improve a vibration resistance. In addition, according to the present embodiment, it is possible to provide the trigger switch  1  which has no tactile feedback and in which a contact force may increase in response to a retraction amount of the trigger  3 . 
     (Variations) 
     According to an aspect of the present invention, it is possible to use a torsion coil spring instead of the flat spring  33 . It is possible that two arms of the torsion coil spring are fixed so that (i) one arm is fixed to one attachment recess  31   d  of a second movable piece  31  and (ii) the other arm is fixed to the other attachment recess  31   d  of the second movable piece  31 . Since a sliding part  6   d  presses a coil part or the like of the coil spring, an effect similar to that of the embodiment above can be produced. 
     Alternatively, it is possible to use an elastic member (spring, rubber, or the like) instead of the flat spring  33 . An elastic member is provided on a second movable piece  31 . Then, a sliding part  6   d  presses the elastic member to cause the elastic member to elastically deform. The elastic member, which has elastically deformed, presses a second movable contact  31   a  against a second fixed contact  31   b , as in the case of the flat spring  33 . The elastic member can have a surface which is inclined with respect to a moving direction of the sliding part  6   d . In such a case, it is possible to (i) prevent an increase in necessary operating force and (ii) press the second movable contact  31   a  against the second fixed contact  31   b . Alternatively, as in the case of the flat spring  33 , the elastic member can have a curved surface which is curved so as to protrude. 
     Note that although the present specification discussed an example in which the trigger switch  1  is included in an electric power tool, the present invention is not limited to such an example. Alternatively, the trigger switch  1  can be provided to any machine in addition to such a tool. Although the present specification discussed an example in which the switch opening-closing mechanism  7  is included in the trigger switch  1 , the present invention is not limited such an example. Alternatively, the switch opening-closing mechanism  7  can be used as a switch of any machine. Although the present specification discussed an example in which the switch opening-closing mechanism  7  includes a first switch and a second switch, the present invention is not limited to such an example. Alternatively, for example, the switch opening-closing mechanism  7  can be configured to include a second switch but not a first switch. 
     The present invention is not limited to the embodiments, but can be altered by a skilled person in the art within the scope of the claims. The present invention also encompasses, in its technical scope, any embodiment derived by combining technical means disclosed in differing embodiments. 
     As has been described, a switch contact structure in accordance with an aspect of the present invention includes: an operation section; a first movable contact member; and a first counter contact member configured to face the first movable contact member, in a case where an amount of movement of the operation section reaches a first movement amount, the first movable contact member coming into contact with the first counter contact member due to a spring force applied to the first movable contact member, and in a case where the amount of movement of the operation section reaches a second movement amount which is larger than the first movement amount, the operation section pressing the first movable contact member against the first counter contact member. 
     With the configuration, it is possible to increase a contact force between the first movable contact member and the first counter contact member so as to improve a vibration resistance. 
     The contact structure in accordance with an aspect of the present invention can be configured so that: the first movable contact member includes an elastic member; and in a case where the amount of movement of the operation section reaches the second movement amount, the operation section presses the first movable contact member so as to cause the elastic member to elastically deform. 
     According to the configuration, the elastic member elastically deforms. This prevents a repulsive force, which is applied to the operation section, from sharply becoming large. It is therefore possible to increase the contact force while good operability is maintained. Hence, tactile feedback during operation can be restricted. 
     The contact structure in accordance with an aspect of the present invention can be configured so that in a case where the amount of movement of the operation section reaches the second movement amount, the operation section comes into contact with the elastic member. 
     With the configuration, it is possible to (i) reduce an effect on an operating load and (ii) increase the contact force as necessary. 
     The contact structure in accordance with an aspect of the present invention configured so that: the elastic member has an inclined surface which is inclined with respect to a direction in which the operation section moves; and the operation section is configured to come into contact with the inclined surface. 
     According to the configuration, the operation section comes into contact with the inclined surface. This prevents a repulsive force, which is applied to the operation section, from sharply becoming large. 
     The contact structure in accordance with an aspect of the present invention configured so that: the elastic member has a curved surface which is curved so as to protrude; and the operation section is configured to come into contact with the curved surface. 
     According to the configuration, the operation section comes into contact with the curved surface. This allows a change in operating load to be continuous. It is therefore possible to achieve good operability. 
     The contact structure in accordance with an aspect of the present invention configured so that the elastic member is a flat spring. 
     With the configuration, good operability and a high durability can be achieved with a simple configuration. 
     The contact structure in accordance with an aspect of the present invention configured so that the elastic member is a torsion coil spring. 
     The contact structure in accordance with an aspect of the present invention configured so that in a case where the amount of movement of the operation section further increases so as to be more than the second movement amount, a force by which the first movable contact member is pressed against the first counter contact member increases. 
     According to the configuration, a repulsive force, which is applied to the operation section, is prevented from sharply becoming large. 
     The contact structure in accordance with an aspect of the present invention can be configured to further include: a second movable contact member; and a second counter contact member configured to face the second movable contact member, in a case where the amount of movement of the operation section reaches a third movement amount which is smaller than the first movement amount, the second movable contact member coming into contact with the second counter contact member due to a spring force applied to the second movable contact member. 
     With the configuration, it is possible to separate the following (i) and (ii) from each other: (i) the second movable contact member and the second counter contact member which are configured to open and close the switch (i.e., to which arc discharge may occur) and (ii) the first movable contact member and the first counter contact member which are configured to maintain the closed state of the switch. It is therefore possible to improve the durability of the contact structure. 
     A trigger switch in accordance with an aspect of the present invention can be configured to include: the contact structure in accordance with the aspect of the present invention, the operation section being configured to move in coordination with a trigger operated by a user. 
     An electric power tool in accordance with an aspect of the present invention can be configured to include the trigger switch in accordance with the aspect of the present invention. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  Trigger switch 
               2  Housing 
               3  Trigger 
               4  Switching lever 
               4   a  Turning shaft part 
               6  Plunger (operation section) 
               6   d ,  6   e  Sliding part (operation section) 
               7  Switch opening-closing mechanism (switch 
             contact structure) 
               8  Printed circuit board 
               10  Base 
               20  First switch 
               21  First movable piece (second movable contact member) 
               21   a  First movable contact 
               21   b  First fixed contact (second counter contact member) 
               21   c  First inhibiting part 
               22  First coil spring 
               30  Second switch 
               31  Second movable piece (first movable contact member) 
               31   a  Second movable contact 
               31   b  Second fixed contact (first counter contact member) 
               31   c  Second inhibiting part 
               32  Second coil spring 
               33  Flat spring (elastic member)