Patent Description:
In disc grinders and other power tools known in the art, a motor switch is turned on by gripping a switch lever provided on the housing of the power tool and the drive force of the motor rotates a tool attached to the device body. A proposed structure for this type of power tool is provided with off-locking means for holding the motor switch in the off state so that the operator does not unintentionally turn the motor switch on, and on-locking means for maintaining the motor switch in the ON state (for example, see Patent Literature <NUM>). Patent Literature <NUM> relates to a device comprising the features outlined in the preamble of claim <NUM>.

However, in the power tool of Patent Literature <NUM>, an on-lock lever constituting the on-locking means is configured to be exposed from the housing at all times so that an operating force can be exerted on the on-lock lever even before performing the operation to turn on the motor. Therefore, when the operator turns on the motor switch while exerting an operating force on the on-lock lever, the operator could enable the on-lock unintentionally. Further, while it is effective to arrange the operating locations of the off-locking means and on-locking means at different positions to suppress mistaken on-locking operations, the on-locking means in the configuration described in Patent Literature <NUM> is positioned rearward of the switch lever. Accordingly, the operator must operate the off-locking means and switch lever with one hand while operating the on-locking means with the other hand. In such cases, the operator's grip can become unstable.

In view of the foregoing, it is an object of the present invention to provide a power tool configured to prevent the operator from enabling the on-lock unintentionally when the motor switch is in the ON state. It is another object of the present invention to provide a power tool having on-locking means with good usability.

In order to attain the object, the present invention provides a working machine according to independent claim <NUM>.

This configuration enhances usability by suppressing the operator from unintentionally enabling the on-lock for maintaining the working machine in the on position.

In the above-described structure, the operating part has a shielding part wherein the shielding part is provided on an outer peripheral wall of the housing so as to form an internal space between the shielding part and the housing. An entire part of the on-locking means is accommodated in the internal space when the operating part is in the off position.

With this structure, when the operating part is in the off position, the entire part of the on-locking means is accommodated in the internal space. Since the on-locking means is accommodated in the internal space and cannot be operated at this time, this configuration enhances usability by preventing the operating part from being in an on-lock state when moving the operating part into the on position by the operator's operation and by suppressing the operator from unintentionally enabling the on-lock for maintaining the working machine in the on position.

In the above-described structure, it is preferable that the portion of the on-locking means protrudes outward from the shielding part when the housing and the operating part is in the on position.

In the above-described structure, it is preferable that the shielding part is formed with a through-hole. The portion of the on-locking means protrudes outward from the shielding part through the through-hole when the operating part is in the on position. Further preferred features of the invention are set forth in the dependent claims.

According to a working machine of the present invention, preventing the operator from enabling the on-lock unintentionally when the motor switch is in the on state can be achieved. Further, according to the present invention, providing a working machine with good usability can be achieved.

Below, a disc grinder <NUM> will be described as an example of the power tool according to a first embodiment of the present invention while referring to <FIG>. <FIG> is a cross-sectional view showing the internal structure of the disc grinder according to the first embodiment.

As shown in <FIG>, the disc grinder <NUM> is provided with a housing <NUM>, a motor <NUM>, a switch lever <NUM>, an on-lock lever <NUM>, and an off-lock lever <NUM>. In <FIG>, "up" is defined as the upward direction, "down" as the downward direction, "front" as the forward direction, and "rear" as the rearward direction. In addition, "right" when viewing the disc grinder <NUM> from the rear will be defined as the rightward direction, and "left" as the leftward direction. The switch lever <NUM> is an example of an operating part of the present invention. The on-lock lever <NUM> is an example of an on-lock operating part of the present invention. The off-lock lever <NUM> is an example of an off-lock operating part of the present invention.

The housing <NUM> forms the outer shell of the disc grinder <NUM>. The housing <NUM> has a tail cover <NUM>, a motor housing <NUM>, a gear cover <NUM>, and the switch lever <NUM>.

The tail cover <NUM> has a substantially cylindrical shape that extends along the front-rear direction. The tail cover <NUM> forms the rear end of the housing <NUM>. The front-end portion of the tail cover <NUM> is connected to the rear end portion of the motor housing <NUM>. A switch <NUM> is accommodated in the tail cover <NUM>. A support part <NUM> extends downward from the bottom surface of the tail cover <NUM>. An anchoring part <NUM> is provided on the bottom surface of the tail cover <NUM> to the rear of the support part <NUM>. A support part <NUM> is provided in the lower rear-end portion of the tail cover <NUM>. The switch lever <NUM> and on-lock lever <NUM> are also attached to the bottom side of the tail cover <NUM>. Further, a power cord <NUM> that connects to an external power supply (not shown) extends from the rear end of the tail cover <NUM>.

The motor housing <NUM> has a substantially cylindrical shape that extends along the front-rear direction. The front-end portion of the motor housing <NUM> is connected to the rear-end portion of the gear cover <NUM>. The motor <NUM> and a cooling fan <NUM> are accommodated in the motor housing <NUM>.

The gear cover <NUM> has a substantially cylindrical shape that extends along the front-rear direction. A power transmission part <NUM> is accommodated in the gear cover <NUM>.

The switch <NUM> has a push button 211a disposed so as to protrude downward from the bottom surface of the switch <NUM>. When the bottom surface of the push button 211a is pressed upward, the push button 211a moves upward. Once the push button 211a has moved a prescribed distance, the switch <NUM> is configured to supply power to the motor <NUM> via the power cord <NUM>.

The motor <NUM> has a rotational shaft <NUM> extending along the front-rear direction. The rotational shaft <NUM> is disposed inside the motor housing <NUM> so that its axial direction is aligned with the front-rear direction. The rotational shaft <NUM> is rotatably supported via a bearing <NUM> that is fixed in the gear cover <NUM>, and a bearing <NUM> that is fixed in the motor housing <NUM>.

The cooling fan <NUM> is positioned to the front of the motor <NUM>. The cooling fan <NUM> is fixed to the rotational shaft <NUM> of the motor <NUM> so as to be capable of rotating together and coaxially with the rotational shaft <NUM>. The cooling fan <NUM> is configured such that its rotating force draws air in through slit-shaped air intake holes <NUM>, passes the air through the motor <NUM>, and exhausts the air through exhaust holes (not shown) formed in the gear cover <NUM>.

The power transmission part <NUM> has bevel gears <NUM> and <NUM>, a bearing <NUM>, and a spindle <NUM>. The power transmission part <NUM> is provided on a power transmission path from the motor <NUM> to a grinding wheel <NUM>, which is the tip tool. The power transmission part <NUM> is configured to transmit the rotating force of the rotational shaft <NUM> (the motor <NUM>) to the grinding wheel <NUM>. The spindle <NUM> is an example of a mounting part of the present invention.

The spindle <NUM> extends downward at a right angle to the rotational shaft <NUM> of the motor <NUM>. The spindle <NUM> is rotatably supported by the bearing <NUM>. The bearing <NUM> is fixed to the gear cover <NUM>. The grinding wheel <NUM>, i.e., the tip tool, is mounted on the bottom end of the spindle <NUM>.

The bevel gear <NUM> is fixed to the front end of the rotational shaft <NUM> in the motor <NUM>. The bevel gear <NUM> rotates together with the rotational shaft <NUM>. The bevel gear <NUM> is disposed forward of the bevel gear <NUM> and meshes with the bevel gear <NUM>. The bevel gear <NUM> is fixed to the top of the spindle <NUM>. The bevel gear <NUM> rotates together and coaxially with the spindle <NUM>. The bevel gear <NUM> has a larger radius than the bevel gear <NUM>.

The grinding wheel <NUM> has a disc-shape and is mounted on the spindle <NUM> via a nut <NUM> so as to be perpendicular to the extending direction of the spindle <NUM>. The grinding wheel <NUM> is configured of a resinoid flexible grinding wheel, a flexible grinding wheel, a resinoid grinding wheel, a sanding disc, or the like having a diameter of <NUM>, for example. Depending on the type of abrasive grains selected for use, the grinding wheel <NUM> can perform flat surface grinding or curved surface grinding of metal, synthetic resin, marble, concrete, and the like. Further, a semicircular wheel guard <NUM> is attached so as to cover the rear half of the grinding wheel <NUM> and is provided to suppress scattering of ground members, damaged grains, and the like.

Next, the configuration of the switch lever <NUM>, on-lock lever <NUM>, and off-lock lever <NUM> according to the first embodiment of the present invention will be described with reference to <FIG>. The switch lever <NUM> extends along the longitudinal direction of the tail cover <NUM> from the rear end toward the front end of the tail cover <NUM>. As shown in <FIG>, the switch lever <NUM> has a bottom portion <NUM>, a front wall portion <NUM>, a left wall <NUM>, a right wall <NUM>, a protruding part <NUM>, a pair of support parts <NUM>, and mounting parts 48a and 48b. The left wall, right wall and bottom portion are an example of a shielding portion of the present invention.

The bottom portion <NUM> has a substantially flat plate shape and forms the bottom of the switch lever <NUM>. The mounting parts 48a and 48b are provided on the top surface of the bottom portion <NUM> at the rear end thereof. The mounting parts 48a and 48b are substantially annular shaped and extend upward from the top surface of the bottom portion <NUM>. The mounting parts 48a and 48b are arranged a prescribed distance apart in the left-right direction. Through-holes 481a and 481b are respectively formed in the mounting parts 48a and 48b and penetrate the same in the left-right direction. The mounting parts 48a and 48b are pivotably fixed to the support part <NUM> (shaft part) of the tail cover <NUM> through a rotational shaft (not shown) penetrating the through-holes 481a and 481b. With this configuration, the switch lever <NUM> can pivot about the support part <NUM> (shaft part) relative to the bottom portion of the tail cover <NUM> in a B1 direction (clockwise) and a B2 direction (counterclockwise) indicated in <FIG>.

A first through-hole <NUM> having a substantially rectangular shape is formed in the bottom portion <NUM> and penetrates the bottom portion <NUM> vertically at a position forward of the position at which the mounting parts 48a and 48b are provided. Further, a second through-hole <NUM> having a substantially rectangular shape is formed in the bottom portion <NUM> and penetrates the bottom portion <NUM> vertically at a position forward of the first through-hole <NUM>. The second through-hole is an example of a through-hole of the present invention.

The support parts <NUM> are configured of a right support part 47A and a left support part (not shown) positioned a prescribed distance apart in the left-right direction. Since the right support part 47A and the left support part (not shown) are configured with left-right symmetry, only the right support part 47A will be described here, while a detailed structural description of the left support part (not shown) will be omitted. The right support part 47A has a general rectangular parallelepiped shape that extends leftward from the right wall <NUM>. The right support part 47A is positioned higher than the first through-hole <NUM>. A receiving groove 47a is formed in the right support part 47A. The receiving groove 47a extends rightward from the left surface of the right support part 47A and opens upward.

The protruding part <NUM> is positioned between the <NUM> and second through-hole <NUM> on the top surface of the bottom portion <NUM>. The protruding part <NUM> has a substantially cylindrical shape and extends upward from the bottom portion <NUM>. The protruding part <NUM> has an anchoring portion <NUM> that possesses a downward-protruding pawl part, and a cylindrical portion <NUM>. The front wall portion <NUM> is positioned on the top surface of the bottom portion <NUM> at the front end thereof and is forward of the first through-hole <NUM>. The front wall portion <NUM> has a flat plate shape and extends upward. The left wall <NUM> and right wall <NUM> are positioned on the top surface of the bottom portion <NUM> at respective left and right edges thereof. The left wall <NUM> and right wall <NUM> are arranged to sandwich the front wall portion <NUM> and protruding part <NUM> from left and right sides. Both the left wall <NUM> and right wall <NUM> have flat plate shapes and extend upward.

As shown in <FIG>, the on-lock lever <NUM> has a substantially flat plate shape. The on-lock lever <NUM> includes an engaging part <NUM> on the upper end thereof, a support part <NUM> positioned in the center portion of the on-lock lever <NUM>, a lever part <NUM> forming the opposite end of the on-lock lever <NUM> from the engaging part <NUM>, a shaft <NUM> having a columnar shape, and a torsion spring <NUM>. A pawl part is provided on the distal end of the engaging part <NUM> and is capable of engaging with the anchoring portion <NUM>. The support part <NUM> has an annular shape in a side view. The shaft <NUM> penetrates a through-hole <NUM> formed in the support part <NUM>. Both ends of the shaft <NUM> are fixed to the support part <NUM> of the tail cover <NUM>. The lever part <NUM> is configured to be pivotable about the shaft <NUM> in a C1 direction (clockwise) and a C2 direction (counterclockwise) in <FIG>. The torsion spring <NUM> is wound around the shaft <NUM> and urges the lever part <NUM> of the on-lock lever <NUM> in the C2 direction.

As shown in <FIG>, the off-lock lever <NUM> has a substantially flat plate shape. The off-lock lever <NUM> includes an inner end portion <NUM> constituting the upper end of the off-lock lever <NUM>, a support part <NUM> positioned in the center portion of the off-lock lever <NUM> and having an annular shape in a side view, a lever part <NUM> forming the opposite end of the off-lock lever <NUM> from the inner end portion <NUM>, a shaft <NUM> having a columnar shape, and a torsion spring <NUM>. The shaft <NUM> penetrates a through-hole <NUM> formed in the support part <NUM>. Both ends of the shaft <NUM> are rotatably fixed in the receiving groove 47a of the right support part 47A and a corresponding receiving groove (not shown) formed in the left support part (not shown) of the switch lever <NUM>. The lever part <NUM> of the off-lock lever <NUM> is configured to be pivotable about the rotational axis of the support part <NUM> in an A1 direction (clockwise) and an A2 direction (counterclockwise) in <FIG>. The torsion spring <NUM> is wound about the shaft <NUM> and urges the lever part <NUM> in the B2 direction.

Next, operations of the disc grinder <NUM> according to the first embodiment and operations of the switch lever <NUM>, on-lock lever <NUM>, and off-lock lever <NUM> will be described with reference to <FIG>. To operate the disc grinder <NUM>, the operator grips the top surface of the tail cover <NUM> with one hand, wrapping the fingers of the hand around the bottom portion <NUM> of the switch lever <NUM>. If needed, the operator may use the other hand to grip the periphery of the motor housing <NUM> or a secondary handle or the like attached to the gear cover <NUM>. The center of gravity of the disc grinder <NUM> is located in the area of the motor <NUM>. Therefore, the operator grips the disc grinder <NUM> with hands on both sides of the center of gravity. The state of the disc grinder <NUM> shown in <FIG> is the state of the disc grinder <NUM> in its initial position in which no external force is being applied to the switch lever <NUM>, on-lock lever <NUM>, and off-lock lever <NUM> and none of the switch lever <NUM>, on-lock lever <NUM>, and off-lock lever <NUM> is being operated. In the initial state of the disc grinder <NUM>, the urging force of the torsion spring <NUM> in the A2 direction (see <FIG>) forces the rear surface of the lever part <NUM> in the off-lock lever <NUM> to contact the inner circumferential surface formed in the first through-hole <NUM>. At this time, the distal end of the lever part <NUM> protrudes out through the first through-hole <NUM>. Further, the inner end portion <NUM> and the anchoring part <NUM> of the tail cover <NUM> are at the same position in the front-rear direction and oppose each other vertically over a prescribed interval. In this initial state, the switch lever <NUM> is halted by its own weight at the lowest position in the allowable pivoting range. In this initial state, the lever part <NUM> of the on-lock lever <NUM> is also halted at its rightmost position in the allowable pivoting range by the urging force of the torsion spring <NUM> in the C2 direction (see <FIG>). The position of the on-lock lever <NUM> at this time will be called the on-lock release position. Here, the engaging part <NUM> and anchoring portion <NUM> are disengaged.

When the disc grinder <NUM> is in this initial state, even if the operator grips the bottom portion <NUM> of the switch lever <NUM> and applies force to the bottom portion <NUM> in the B1 direction shown in <FIG>, the top surface of the inner end portion <NUM> in the off-lock lever <NUM> is configured to contact the bottom surface of the anchoring part <NUM> on the tail cover <NUM>, preventing the switch lever <NUM> from pivoting more than a prescribed angle. Therefore, the protruding part <NUM> does not press the push button 211a provided for driving the motor <NUM>. The position of the off-lock lever <NUM> at this time will be called the off-lock position. Further, the position of the switch lever <NUM> when the bottom portion <NUM> is in the position shown in <FIG> and the protruding part <NUM> is not pressed against the push button 211a will be called the OFF position. When the switch lever <NUM> is in the OFF position, an internal space <NUM> is formed. The internal space <NUM> is surrounded by the bottom portion <NUM>, front wall portion <NUM>, left wall <NUM>, right wall <NUM>, protruding part <NUM>, and the outer surface on the bottom of the tail cover <NUM>. The internal space <NUM> is an example of an internal space of the present invention.

When the switch lever <NUM> is in the OFF position as shown in <FIG>, the entire lever part <NUM> of the on-lock lever <NUM> is accommodated in the internal space <NUM>. Since the lever part <NUM> of the on-lock lever <NUM> is accommodated in the internal space <NUM> and cannot be operated at this time, the operator cannot operate the on-lock lever <NUM> to enable the on-lock at a stage prior to operating the switch lever <NUM>. This configuration enhances usability of the disc grinder <NUM> by ensuring the operator does not unintentionally enable the on-lock for maintaining the disc grinder in an ON state when moving the switch lever <NUM> into the ON position for pressing the push button 211a to drive the motor <NUM>.

When the operator exerts force on the lever part <NUM> of the off-lock lever <NUM> in the A1 direction of <FIG> to pivot the lever part <NUM> about the rotational axis of the support part <NUM> while the disc grinder <NUM> is in this initial state, the inner end portion <NUM> moves rearward, expanding the vertical gap between the anchoring part <NUM> and the off-lock lever <NUM>, and enables the bottom portion <NUM> of the switch lever <NUM> to pivot in the B1 direction. While no external force is applied to the switch lever <NUM> and on-lock lever <NUM> at this time, the switch lever <NUM> and on-lock lever <NUM> remain in the initial position. The position of the off-lock lever <NUM> in the state shown in <FIG> in which the vertical gap between the anchoring part <NUM> and the off-lock lever <NUM> is sufficient to allow the bottom portion <NUM> to pivot in the B1 direction will be called the off-lock release position. When the off-lock lever <NUM> is in the off-lock release position and the on-lock lever <NUM> is in the on-lock release position, the bottom portion <NUM> of the switch lever <NUM> can pivot in the B1 direction.

In the state of <FIG>, if the operator applies force to the bottom portion <NUM> of the switch lever <NUM> in the B1 direction while continuing to exert force on the lever part <NUM> of the off-lock lever <NUM> to maintain the off-lock lever <NUM> in the off-lock release position, the bottom portion <NUM> pivots in the B1 direction about the rotational axis of the support part <NUM>. At this time, no external force is being applied to the on-lock lever <NUM>, and the on-lock lever <NUM> remains in its initial position. Since the protruding part <NUM> moves in the same direction with the bottom portion <NUM>, the protruding part <NUM> moves upward as the bottom portion <NUM> pivots in the B1 direction and presses against the push button 211a of the switch <NUM> to turn the switch <NUM> on. Accordingly, power is supplied from the external power supply to the motor <NUM> via the power cord <NUM>, driving the motor <NUM> (<FIG>). The position of the switch lever <NUM> when the bottom portion <NUM> is in the position shown in <FIG> and the protruding part <NUM> is pressed against the push button 211a will be called the ON position.

When the motor <NUM> is driven, the bevel gear <NUM> that rotates together and coaxially with the rotational shaft <NUM> of the motor <NUM> rotates. The rotational force of the bevel gear <NUM> is transmitted to the bevel gear <NUM> meshed with the bevel gear <NUM> and the bevel gear <NUM> rotates. The spindle <NUM> that rotates together and coaxially with the bevel gear <NUM> rotates along with the rotation of the bevel gear <NUM>, and the grinding wheel <NUM> mounted on the bottom end of the spindle <NUM> rotates. The drive force of the motor <NUM> is decelerated according to the ratio of radii (gear ratio) for the bevel gear <NUM> and bevel gear <NUM> and transmitted to the spindle <NUM>.

When the operator pivots the bottom portion <NUM> in the B1 direction, a portion of the lever part <NUM> on the on-lock lever <NUM> accommodated in the internal space <NUM> protrudes out through the second through-hole <NUM> formed in the bottom portion <NUM> as the switch lever <NUM> moves. Accordingly, the operator can operate the lever part <NUM>, i.e., can apply external force to the lever part <NUM> (see <FIG>). The front surface of the inner end portion <NUM> in <FIG> contacts the bottom surface of the tail cover <NUM> at this time, as illustrated in <FIG>. Hence, the lever part <NUM> will not pivot in the A2 direction even if the operator releases the lever part <NUM> of the off-lock lever <NUM>.

Since the anchoring portion <NUM> rises as the switch lever <NUM> rises, if the operator pivots the lever part <NUM> about the rotational axis of the support part <NUM> constituting the on-lock lever <NUM> to move the lever part <NUM> substantially forward in the C1 direction (clockwise) relative to the switch lever <NUM> while the switch lever <NUM> is maintained in the ON position shown in <FIG>, the engaging part <NUM> moves substantially rearward to become positioned beneath the anchoring portion <NUM> (see <FIG>). At this time, the front surface of the inner end portion <NUM> on the off-lock lever <NUM> remains in contact with the bottom surface of the tail cover <NUM>. While holding the lever part <NUM> with a finger against the urging force of the torsion spring <NUM>, the operator gradually lightens the gripping force on the bottom portion <NUM> while the front-side surface of the lever part <NUM> contacts the inner circumferential surface formed in the second through-hole <NUM>. Consequently, the switch lever <NUM> pivots in the B2 direction (counterclockwise) by the urging force of the push button 211a, and the pawl part of the anchoring portion <NUM> provided on the switch lever <NUM> moves downward along with the switch lever <NUM> until the pawl part of the engaging part <NUM> engages with the pawl part of the anchoring portion <NUM> (<FIG>). At this time, the engaging part <NUM> inhibits movement of the anchoring portion <NUM>, even after the operator releases the lever part <NUM> of the on-lock lever <NUM>. Further, the front-side surface of the lever part <NUM> is maintained in contact with the inner circumferential surface of the second through-hole <NUM> through the urging force of the push button 211a. Since the engaged state of the engaging part <NUM> and anchoring portion <NUM> is maintained, the switch lever <NUM> is restricted from pivoting in the B2 direction. More specifically, the contact between the front-side surface of the lever part <NUM> and the inner circumferential surface of the second through-hole <NUM> owing to the engagement between the pawl part of the engaging part <NUM> on the on-lock lever <NUM> supported on the tail cover <NUM> and the pawl part of the anchoring portion <NUM> on the switch lever <NUM> halts pivoting of the switch lever <NUM> in the B2 direction. At this time, the switch lever <NUM> is maintained in the ON position, even when the operator releases the switch lever <NUM>, and the motor <NUM> continues driving. The position of the on-lock lever <NUM> in this state will be called the on-lock position. In this state, the motor <NUM> is driving while operations of the switch lever <NUM>, on-lock lever <NUM>, and off-lock lever <NUM> are all halted. This state will be called the on-lock state of the disc grinder <NUM>.

Next, the operations performed when halting operation of the disc grinder <NUM> will be described. When the disc grinder <NUM> is in the on-lock state (see <FIG>) and the operator grips the switch lever <NUM> and applies force in the B1 direction, the anchoring portion <NUM> provided on the switch lever <NUM> moves upward relative to the on-lock lever <NUM>. Hence, the pawl part of the anchoring portion <NUM> separates from the pawl part of the engaging part <NUM>, disengaging the two (see <FIG>). Consequently, the urging force of the torsion spring <NUM> pivots the lever part <NUM> of the on-lock lever <NUM> in the C2 direction. The lever part <NUM> pivots toward the on-lock release position and stops when the rear surface of the lever part <NUM> contacts the inner circumference surface in the second through-hole <NUM> (see <FIG>). By releasing the engagement between the pawl part of the anchoring portion <NUM> and the pawl part of the engaging part <NUM>, the switch lever <NUM> can pivot in the B2 direction. When the operator releases the switch lever <NUM>, the switch lever <NUM> pivots farther in the B2 direction owing to the urging force of the torsion spring (not shown). Movement of the switch lever <NUM> is halted at the OFF position (<FIG>). The vertical distance between the tail cover <NUM> and the distal end of the switch lever <NUM> on the front side of the bottom portion <NUM> expands as the switch lever <NUM> pivots. Once this vertical distance reaches a prescribed value, the front surface on the inner end portion <NUM> of the off-lock lever <NUM> separates from the bottom surface on the tail cover <NUM>. Accordingly, the lever part <NUM> of the off-lock lever <NUM> is pivoted in the A2 direction by the urging force of the torsion spring <NUM> and comes to a halt when the rear surface of the lever part <NUM> contacts the inner circumferential surface formed in the first through-hole <NUM>. Further, the top surface of the protruding part <NUM> moves in a direction away from the push button 211a as the switch lever <NUM> pivots in the B2 direction. When this distance of separation reaches a prescribed magnitude, power supplied from the external power supply to the motor <NUM> via the power cord <NUM> is stopped, and the motor <NUM> stops driving. At this time, the drive of the motor <NUM> and operations of the switch lever <NUM>, on-lock lever <NUM>, and off-lock lever <NUM> are all halted, and the disc grinder <NUM> is back in its initial state (see <FIG>).

In order to maintain a stable grip on the disc grinder <NUM>, the operator must hold the front of the disc grinder <NUM> with one hand and the rear with the other while performing a sequence of operations including, in order, operating the off-lock lever <NUM> to release the off-lock, moving the switch lever <NUM> to the ON position, and operating the on-lock lever <NUM> to enable the on-lock. At this time, since the position of the on-lock lever <NUM> in the front-rear direction overlaps the position of the switch lever <NUM>, the operator can easily operate the on-lock lever <NUM> with the same hand used to operate the switch lever <NUM> and need not change grips. Hence, stable work can be performed. Further, since the on-lock lever <NUM> is disposed at a position farther forward than the off-lock lever <NUM>, movement of the hand that operates the on-lock lever <NUM> after operating the off-lock lever <NUM> is limited to the forward direction so that the gripping position need not become distanced from heavy components (the motor <NUM> and gear cover <NUM>). Further, while one hand operates the off-lock lever <NUM>, the other hand gripping the front can easily be used to operate the on-lock lever <NUM>, thereby improving usability as a whole.

The disc grinder <NUM> is further configured so that at least part of the lever part <NUM> on the on-lock lever <NUM> is accommodated in the housing <NUM> (the tail cover <NUM> and switch lever <NUM>) when the switch lever <NUM> is in the OFF position (the initial position), and the same portion of the lever part <NUM> is exposed outside the housing <NUM> (the switch lever <NUM>) when the switch lever <NUM> is in the ON position. Hence, applying force to the on-lock lever <NUM> is more difficult when the switch lever <NUM> is in the OFF position than when the switch lever <NUM> is in the ON position, reducing the likelihood that the operator will enable the on-lock unintentionally while the switch lever <NUM> is in the ON position and cause the switch lever <NUM> to be maintained in the ON position, thereby enhancing usability. Further, since the on-lock lever <NUM> is protected by the switch lever <NUM> in a non-working state, there is little chance that the on-lock lever <NUM> will suffer impacts when the disc grinder <NUM> is dropped, for example, thereby suppressing damage to the on-lock lever <NUM>, which is a relatively small part.

The disc grinder <NUM> is also configured such that the moving direction of the lever part <NUM> when the off-lock lever <NUM> moves from the off-lock position toward the off-lock release position is opposite the moving direction of the lever part <NUM> when the on-lock lever <NUM> moves from the on-lock position toward the on-lock release position. This configuration avoids the user confusing operations of the off-lock lever <NUM> with operations of the on-lock lever <NUM>, thereby further enhancing usability.

The disc grinder serving as an example of the power tool according to the first embodiment of the present invention is not limited to the embodiment described above and may be modified and improved in various ways without departing from the spirit of the invention, the scope of which is defined by the attached claims. For example, in the first embodiment described above the entire lever part <NUM> of the on-lock lever <NUM> is accommodated in the internal space <NUM> when the switch lever <NUM> is in the OFF position, and the lever part <NUM> protrudes outside of the second through-hole <NUM> when the switch lever <NUM> is in the ON position. However, in place of the above configuration, at least a portion of the lever part <NUM> on the on-lock lever <NUM> may be accommodated in the internal space <NUM> when the switch lever <NUM> is in the ON position, and the volume of the lever part <NUM> positioned inside the internal space <NUM> may vary according to the position of the switch lever <NUM>. That is, the amount that the lever part <NUM> protrudes from the internal space <NUM> when the switch lever <NUM> is in the ON position should be greater than the amount that the lever part <NUM> protrudes from the internal space <NUM> when the switch lever <NUM> is in the OFF position. This configuration still makes it more difficult to operate the lever part <NUM> when the switch lever <NUM> is in the OFF position, i.e., prior to performing an operation to turn on the motor <NUM>, than to operate the lever part <NUM> when the switch lever <NUM> is in the ON position. Accordingly, this configuration prevents the disc grinder <NUM> from entering the on-lock state when the switch lever <NUM> is placed in the ON position and suppresses the operator from unintentionally enabling the on-lock for maintaining the switch lever <NUM> in the ON position. Thus, this configuration can enhance usability. Further, while the mechanical structure of the on-lock lever <NUM> serves as the on-locking means for maintaining the motor <NUM> in a driving state, the on-lock lever <NUM> may be replaced with an electronic push switch. In this case, the on-locking means is positioned inside the housing <NUM> and, hence, it is still difficult to apply external force to the on-locking means prior to performing an operation to turn on the motor <NUM>, thereby suppressing the operator from unintentionally operating the on-locking means.

Next, a disc grinder <NUM> will be described as an example of the power tool according to a second embodiment of the present invention while referring to <FIG>. The disc grinder <NUM> has essentially the same structure as the disc grinder <NUM> according to the first embodiment. Components identical to those in the disc grinder <NUM> are designated with the same reference numerals to avoid duplicating description. The following description will primarily cover different structures and structures that need to be described in greater detail. Structures identical to those of the disc grinder <NUM> obtain the same effects as described above.

As shown in <FIG>, the disc grinder <NUM> according to the second embodiment is provided with a tail cover <NUM> in place of the tail cover <NUM>. An anchoring part <NUM> is provided inside the tail cover <NUM> and extends downward to a position lower than the switch <NUM>. A second anchoring part <NUM> is provided in the rear end of the tail cover <NUM> and extends upward from the bottom of the tail cover <NUM>. In the disc grinder <NUM> according to the second embodiment, a switch lever part <NUM> is provided in place of the switch lever <NUM>. The switch lever part <NUM> extends along the front-rear direction parallel to the motor housing <NUM> and the tail cover <NUM>. The disc grinder <NUM> according to the second embodiment is also provided with an on-lock lever <NUM> (<FIG>) in place of the on-lock lever <NUM>. The on-lock lever <NUM> has an engaging part <NUM>. A torsion spring <NUM> of the on-lock lever <NUM> urges a lever part <NUM> in the clockwise direction of <FIG>. When moving the on-lock lever <NUM> to the on-lock position, the operator pivots the lever part <NUM> counterclockwise against the urging force of the torsion spring <NUM>. The disc grinder <NUM> according to the second embodiment is also provided with an off-lock part <NUM> in place of the off-lock lever <NUM>. The off-lock part <NUM> extends along the front-rear direction parallel to the motor housing <NUM> and the tail cover <NUM>.

The switch lever part <NUM> has a flat part <NUM>, an engaging part <NUM>, a first protruding part <NUM>, a second protruding part <NUM>, a rear portion <NUM>, and a spring <NUM>. The flat part <NUM> has a flat plate shape and extends along the front-rear direction. The front end of the flat part <NUM> is supported on the bottom of the motor housing. When an upward external force is applied to the bottom surface of the flat part <NUM>, the switch lever part <NUM> can pivot about the front end of the flat part <NUM>. The engaging part <NUM> has an inverted L-shape in a side view and extends upward from the rear end of the flat part <NUM>. A pawl part is provided on the distal end of the engaging part <NUM>. The first protruding part <NUM> is substantially triangular shaped in a side view. The first protruding part <NUM> is positioned to the rear of the engaging part <NUM> and extends upward from the top surface of the switch lever part <NUM>. The second protruding part <NUM> is substantially triangular shaped in a side view. The second protruding part <NUM> extends upward from the top surface of the switch lever part <NUM>. The top surface of the second protruding part <NUM> confronts the bottom surface of the push button 211a. The rear portion <NUM> forms the rear end of the switch lever part <NUM> and has an inverted L-shape in a side view. The rear portion <NUM> has a pawl part that extends rearward. The bottom surface of the pawl part is positioned above the top surface of the second anchoring part <NUM>. The spring <NUM> is wound around the first protruding part and extends upward from the top surface of the switch lever part <NUM>. The top end of the spring <NUM> is fixed to a portion of the tail cover <NUM>. The spring <NUM> urges the switch lever part <NUM> downward. A through-hole <NUM> is formed in the switch lever part <NUM>. The through-hole <NUM> penetrates the switch lever part <NUM> vertically at a position between the engaging part <NUM> and first protruding part <NUM> in the front-rear direction.

The off-lock part <NUM> has a lever part <NUM>, a coupling part <NUM>, a third protruding part <NUM>, a spring <NUM>, and a braking part <NUM>. The lever part <NUM> is supported from below by the switch lever part <NUM> so as to be capable of sliding in the front-rear direction relative to the switch lever part <NUM>. The coupling part <NUM> is configured of a plurality of flat plate-shaped members coupled together and extends along the front-rear direction. The bottom surface on the front-end portion of the coupling part <NUM> contacts the inside surface on the bottom wall of the motor housing <NUM>. The bottom surface on the center portion of the coupling part <NUM> contacts the top surface on the front portion of the switch lever part <NUM>. The rear-end portion of the coupling part <NUM> is connected to the front-end portion of the lever part <NUM>. A through-hole 1062a is formed in the coupling part <NUM> and penetrates the coupling part <NUM> vertically at the same position in the front-rear direction as the through-hole <NUM>. The on-lock lever <NUM> is disposed in the through-hole 1062a. The third protruding part <NUM> is substantially rectangular shaped in a side view. The third protruding part <NUM> is positioned in the center of the lever part <NUM> relative to the front-rear direction and extends upward from the top surface of the lever part <NUM>. A protrusion is provided on the upper end of the third protruding part <NUM> and protrudes upward therefrom. The spring <NUM> extends in the front-rear direction and is disposed between the first protruding part <NUM> and the third protruding part <NUM> in the front-rear direction. The spring <NUM> urges the third protruding part <NUM> rearward.

The braking part <NUM> has a contact part <NUM>, a pressing part <NUM>, a pair of brake pads <NUM>, an intermediate part <NUM>, a protruding part <NUM>, a hooking part <NUM>, a spring <NUM>, and a spring <NUM>. The contact part <NUM> has an annular shape with a through-hole formed in the center portion. The contact part <NUM> is positioned forward of the cooling fan <NUM>. The rotational shaft <NUM> of the motor <NUM> is fixed in the through-hole formed in the contact part <NUM>. With this arrangement, the rotational shaft <NUM> and the pressing part <NUM> can rotate together about an axis extending in the front-rear direction. The pressing part <NUM> has an annular shape with a through-hole formed in the center portion. The pressing part <NUM> is positioned forward of the contact part <NUM>. The rotational shaft <NUM> is inserted through the through-hole of the pressing part <NUM>. The pressing part <NUM> is supported in the motor housing <NUM> so as to be capable of moving in the front-rear direction. The through-hole formed in the center portion of the pressing part <NUM> has a larger diameter than the outer diameter of the rotational shaft <NUM>. The brake pads <NUM> are provided on the rear surface of the pressing part <NUM> so as to be symmetrical about the axial center of the rotational shaft <NUM>. The intermediate part <NUM> has an annular shape with a through-hole formed in the center portion thereof. The rotational shaft <NUM> is inserted through the through-hole. The through-hole formed in the center portion of the intermediate part <NUM> has a larger diameter than the outer diameter of the rotational shaft <NUM>. While no external force is acting on the disc grinder <NUM>, the rear surface of the intermediate part <NUM> is in contact with the front surface of the pressing part <NUM>, the rear surface on the top end of the intermediate part <NUM> is in contact with the inner circumferential surface of the motor housing <NUM>, and the bottom end of the intermediate part <NUM> is connected to the coupling part <NUM>. The intermediate part <NUM> is supported in the motor housing <NUM> so as to be capable of pivoting about a rotational axis (not shown) near the surface of the intermediate part <NUM> that contacts the inner circumferential surface of the motor housing <NUM>. The protruding part <NUM> is substantially rectangular shaped in a side view. The protruding part <NUM> protrudes rearward from the left side of the inner circumferential surface forming the through-hole in the pressing part <NUM>. The hooking part <NUM> has an L-shape in a side view. The hooking part <NUM> protrudes rearward from the rear surface of the intermediate part <NUM> at a position above the protruding part <NUM>. A pawl part is provided on the rear end of the hooking part <NUM> and extends downward therefrom. The spring <NUM> is disposed between the front surface of the pressing part <NUM> and the inner surface of the motor housing <NUM> in the front-rear direction. The rotational shaft <NUM> is inserted through the spring <NUM>. The spring <NUM> extends in the front-rear direction and urges the pressing part <NUM> rearward. The spring <NUM> extends in the front-rear direction at a position above the rotational shaft <NUM>. The spring <NUM> is a tension spring disposed between the front surface of the intermediate part <NUM> and the inside surface of the motor housing <NUM> in the front-rear direction. The spring <NUM> urges the intermediate part <NUM> rearward. Through the urging force of the spring <NUM>, the coupling part <NUM> is urged rearward via the intermediate part <NUM>.

Next, operations of the disc grinder <NUM> according to the second embodiment and operations of the switch lever <NUM>, on-lock lever <NUM>, and off-lock lever <NUM> will be described with reference to <FIG>.

To operate the disc grinder <NUM>, the operator supports the switch lever part <NUM> around the flat part <NUM> or the gear cover with one hand and grips the off-lock part <NUM> around the lever part <NUM> with the other hand. The state of the disc grinder <NUM> shown in <FIG> is the state in which no external force is being applied to the switch lever part <NUM>, on-lock lever <NUM>, and off-lock part <NUM>, and none of the switch lever part <NUM>, on-lock lever <NUM>, and off-lock part <NUM> is being operated. In this state, the lever part <NUM> of the off-lock part <NUM> is halted in the rearmost position of its slidable range by the urging force of the spring <NUM>. At this time, the top surface of the protrusion on the third protruding part <NUM> vertically opposes the bottom surface of the anchoring part <NUM> on the tail cover <NUM> at a prescribed distance. In this initial state, the switch lever part <NUM> is also urged substantially downward relative to the tail cover <NUM> in the B2 direction (<FIG>) by the spring <NUM> and is halted in the lowermost position within the pivotable range of the switch lever part <NUM>. The lever part <NUM> of the on-lock lever <NUM> is also halted in the leftmost position of its pivotable range by the urging force of the torsion spring <NUM> in the C1 direction (<FIG>). The position of the on-lock lever <NUM> at this time will be called the on-lock release position. The engaging part <NUM> and the engaging part <NUM> are not engaged at this time. Further, in the initial state, the rear surfaces of the brake pads <NUM> are in contact with the front surface of the contact part <NUM> provided on the rotational shaft <NUM>. Since the urging force of the spring <NUM> presses the front surface of the contact part <NUM> against the rear surfaces of the brake pads <NUM> through the pressing part <NUM>, frictional force between the rear surfaces of the brake pads <NUM> and the front surface of the contact part <NUM> restrains rotation of the rotational shaft <NUM>, even if the push button 211a were accidentally pressed to drive the motor <NUM>. The state of the braking part <NUM> at this time will be called the brake enabled state.

Even if the operator were to apply an external force to the switch lever part <NUM> in the B1 direction shown in <FIG> while none of the switch lever part <NUM>, on-lock lever <NUM>, and off-lock part <NUM> is being operated, the top surface of the protrusion on the third protruding part <NUM> is configured to contact the bottom surface of the anchoring part <NUM>, preventing the flat part <NUM> from pivoting more than a prescribed angle. Accordingly, the second protruding part <NUM> does not press against the push button 211a that serves to drive the motor <NUM>. The position of the off-lock part <NUM> at this time will be called the off-lock position. Further, the position of the switch lever part <NUM> when the flat part <NUM> is in the position shown in <FIG> and the second protruding part <NUM> is not pressed against the push button 211a will be called the OFF position. When the switch lever part <NUM> is in the OFF position, an internal space <NUM> is formed (<FIG>). The internal space <NUM> is surrounded by the inner circumferential surface forming the through-hole 1062a, and the inner circumferential surface forming the through-hole <NUM>.

When the switch lever part <NUM> is in the OFF position as shown in <FIG>, the entire lever part <NUM> of the on-lock lever <NUM> is accommodated in the internal space <NUM>. At this time, an external force cannot easily be applied to the lever part <NUM> of the on-lock lever <NUM> since the lever part <NUM> is accommodated in the internal space <NUM>. Accordingly, the operator cannot apply force to the on-lock lever <NUM> at a stage prior to operating the switch lever part <NUM>, thereby suppressing the operator from enabling the on-lock unintentionally.

When the operator applies force to the lever part <NUM> of the off-lock part <NUM> in the A1 direction shown in <FIG> to slide the lever part <NUM> forward, the third protruding part <NUM> provided on the lever part <NUM> slides forward relative to the anchoring part <NUM>. As a result, the top end of the third protruding part <NUM> no longer confronts the anchoring part <NUM> vertically (<FIG>), and the flat part <NUM> can now pivot in the B1 direction. The coupling part <NUM> also slides in the A1 direction along with the lever part <NUM>, and the front end of the coupling part <NUM> pushes the bottom end of the intermediate part <NUM> forward. Consequently, the intermediate part <NUM> pivots clockwise in <FIG> about the upper end of the intermediate part <NUM>. Since the hooking part <NUM> provided on the intermediate part <NUM> pivots clockwise as a result, the pawl part forming the rear end of the hooking part <NUM> contacts the protruding part <NUM> provided on the pressing part <NUM> (<FIG>). The hooking part <NUM> pivots further clockwise, and the pressing part <NUM> moves substantially forward relative to the motor housing together with the protruding part <NUM> against the urging force of the spring <NUM>. Accordingly, the rear surfaces of the brake pads <NUM> provided on the pressing part <NUM> separate from the front surface of the contact part <NUM>. The state of the braking part <NUM> at this time will be called a brake release state. At this time, the switch lever part <NUM> and on-lock lever <NUM> remain in their initial positions while no force is applied to the switch lever part <NUM> and on-lock lever <NUM>. When the off-lock part <NUM> is at the position shown in <FIG>, the top end of the third protruding part <NUM> no longer opposes the anchoring part <NUM> vertically, and a sufficient vertical gap exists below the bottom surface of the tail cover <NUM>. The position of the off-lock part <NUM> when the flat part <NUM> is allowed to pivot in the B1 direction will be called the off-lock release position. When the off-lock part <NUM> of the disc grinder <NUM> is in the off-lock release position and the on-lock lever <NUM> is in the on-lock release position, the switch lever part <NUM> can pivot in the B1 direction.

In the state of <FIG>, when the operator grips the flat part <NUM> of the switch lever part <NUM> and applies force to the flat part <NUM> in the B1 direction while continuing to exert force on the lever part <NUM> of the off-lock part <NUM> against the urging force of the spring <NUM> in order to maintain the off-lock part <NUM> in the off-lock release position, the flat part <NUM> pivots in the B1 direction about a rotational axis (not shown) positioned at the front end of the flat part <NUM>. At this time, no external force is being applied to the on-lock lever <NUM>, and the on-lock lever <NUM> remains in the initial position. Further, the braking part <NUM> is in the brake release state. The second protruding part <NUM> provided on the switch lever part <NUM> moves upward as the flat part <NUM> pivots in the B1 direction and presses against the push button 211a of the switch <NUM>. Accordingly, power is supplied from the external power supply (not shown) to the motor <NUM> via the power cord <NUM>, driving the motor <NUM> (<FIG>). The position of the switch lever part <NUM> when the flat part <NUM> is in the position shown in <FIG> and the second protruding part <NUM> is pressed against the push button 211a will be called the ON position.

When the operator pivots the flat part <NUM> in the B1 direction, a portion of the lever part <NUM> constituting the on-lock lever <NUM> accommodated in the internal space <NUM> protrudes out through the through-hole <NUM> formed in the switch lever part <NUM> as the switch lever part <NUM> moves. Accordingly, the operator can now operate the lever part <NUM> (<FIG>). As shown in <FIG>, the top surface of the protrusion on the third protruding part <NUM> is positioned higher than the bottom surface of the anchoring part <NUM> at this time, and the protrusion on the third protruding part <NUM> is positioned forward of the anchoring part <NUM> by a prescribed distance.

When the operator pivots the lever part <NUM> about the rotational axis of the support part <NUM> for the on-lock lever <NUM> in the C2 direction (counterclockwise) in <FIG> while the switch lever part <NUM> is maintained in the ON position shown in <FIG>, the engaging part <NUM> moves substantially forward to become positioned beneath the pawl part of the engaging part <NUM> (<FIG>). At this time, the top surface of the protrusion on the third protruding part <NUM> is positioned higher than the bottom surface of the anchoring part <NUM>, and the rear surface of the protrusion on the third protruding part <NUM> remains a prescribed distance forward of the front surface on the anchoring part <NUM>. If the operator gradually lightens the force of grip on the flat part <NUM> while holding the lever part <NUM> with a finger against the urging force of the torsion spring <NUM> to maintain the lever part <NUM> in the rightmost position within its pivotable range, the switch lever part <NUM> is pivoted in the B2 direction (clockwise) about the front end of the flat part <NUM> by the urging force of the spring <NUM>. Accordingly, the pawl part of the engaging part <NUM> provided on the switch lever part <NUM> moves downward and engages with the pawl part on the engaging part <NUM> (<FIG>). At this time, the urging force of the spring <NUM> that urges the switch lever part <NUM> in the B2 direction to lower the engaging part <NUM> provided on the switch lever part <NUM> side is greater than the urging force of the torsion spring <NUM> that urges the engaging part <NUM> in the C1 direction. Consequently, even if the operator releases the lever part <NUM> of the on-lock lever <NUM>, the engagement between the engaging part <NUM> and engaging part <NUM> is maintained, i.e., the pawl part on the engaging part <NUM> and pawl part on the engaging part <NUM> do not disengage unless a prescribed force is applied. The switch lever part <NUM> is stopped from pivoting in the B2 direction by this engagement between the pawl part on the engaging part <NUM> of the on-lock lever <NUM> supported on the tail cover <NUM> and the pawl part of the engaging part <NUM> on the switch lever part <NUM>. When the operator releases the lever part <NUM>, the rear surface of the protrusion on the third protruding part <NUM> contacts the front surface of the anchoring part <NUM> and stops the lever part <NUM> from sliding rearward at this time (<FIG>). Further, the switch lever part <NUM> is maintained in the ON position when the operator releases the flat part <NUM>, and the motor <NUM> continues driving. The position of the on-lock lever <NUM> in this state will be called the on-lock position. At this time, the motor <NUM> is driving while operations of the switch lever part <NUM>, on-lock lever <NUM>, and off-lock part <NUM> are all halted. The braking part <NUM> is in the brake release state. This state will be called the on-lock state of the disc grinder <NUM>.

Next, the operations performed when halting operation of the disc grinder <NUM> will be described. When the disc grinder <NUM> is in the on-lock state (see <FIG>) and the operator grips the switch lever part <NUM> and applies force in the B1 direction, the engaging part <NUM> provided on the switch lever part <NUM> moves upward relative to the on-lock lever <NUM>. Hence, the pawl part of the engaging part <NUM> separates from the pawl part of the engaging part <NUM>, disengaging the two. Consequently, the urging force of the torsion spring <NUM> pivots the lever part <NUM> of the on-lock lever <NUM> in the C1 direction. The lever part <NUM> pivots toward the on-lock release position and stops at the leftmost position within its pivotable range (<FIG>). By releasing the engagement between the pawl part of the engaging part <NUM> and the pawl part of the engaging part <NUM>, the switch lever part <NUM> can pivot in the B2 direction. When the operator releases the flat part <NUM>, the flat part <NUM> pivots farther in the B2 direction owing to the urging force of the spring <NUM>. Movement of the switch lever part <NUM> is halted at the OFF position (<FIG>). At the same time, the lever part <NUM> of the off-lock part <NUM> is slid in the A2 direction by the urging force of the spring <NUM> and comes to a halt at the rearmost position in its slidable range. At this time, the urging force of the spring <NUM> presses the brake pads <NUM> provided on the pressing part <NUM> against the front surface of the contact part <NUM>, placing the braking part <NUM> in the brake enabled state. The top surface of the second protruding part <NUM> also moves in a direction away from the push button 211a as the flat part <NUM> pivots in the B2 direction. When the second protruding part <NUM> has moved a prescribed distance away from the push button 211a, power supplied from the external power supply to the motor <NUM> via the power cord <NUM> is stopped, and the motor <NUM> stops driving. At this time, the drive of the motor <NUM> and operations of the switch lever part <NUM>, on-lock lever <NUM>, and off-lock part <NUM> are all halted (<FIG>). Since the on-lock lever <NUM> is accommodated in the housing when the switch lever part <NUM> is in the OFF positionin the preferred embodiment, an external force cannot easily be applied to the on-lock lever <NUM>, restraining the disc grinder <NUM> from being placed in the on-lock state unintentionally.

Next, a disc grinder <NUM> will be described as an example of the power tool according to a third embodiment of the present invention while referring to <FIG>. The disc grinder <NUM> has essentially the same structure as the disc grinder <NUM> according to the second embodiment. Components identical to those in the disc grinder <NUM> are designated with the same reference numerals to avoid duplicating description. The following description will primarily cover different structures and structures that need to be described in greater detail. Structures identical to those of the disc grinder <NUM> obtain the same effects as described above.

As shown in <FIG>, the disc grinder <NUM> according to the third embodiment is provided with a tail cover <NUM> in place of the tail cover <NUM>. The tail cover <NUM> has a wall part <NUM>. A through-hole 2211a extending along the front-rear direction is formed in the wall part <NUM>. The disc grinder <NUM> according to the third embodiment is also provided with a sliding part <NUM> in place of the switch lever part <NUM> and off-lock part <NUM>. The disc grinder <NUM> according to the third embodiment is also provided with an on-lock lever <NUM> in place of the on-lock lever <NUM>. An engaging part <NUM> is formed on the top end of the on-lock lever <NUM>, and a lever part <NUM> is formed on the bottom end of the on-lock lever <NUM>. The on-lock lever <NUM> also has a torsion spring <NUM> in place of the torsion spring <NUM>. The torsion spring <NUM> urges the lever part <NUM> counterclockwise. When moving the on-lock lever <NUM> to the on-lock position, the operator pivots the lever part <NUM> clockwise in <FIG>. A linkage part <NUM> is provided on the inner surface of the bottom wall constituting the motor housing <NUM> of the disc grinder <NUM> according to the third embodiment. The linkage part <NUM> has a flat plate shape and extends along the front-rear direction. The front end of the linkage part <NUM> is connected to the bottom end of the intermediate part <NUM>.

The sliding part <NUM> extends along the front-rear direction parallel to the motor housing <NUM> and the tail cover <NUM>. The sliding part <NUM> is supported on the motor housing <NUM> and tail cover <NUM> so as to be capable of sliding in the front-rear direction. The bottom surface on the front end of the sliding part <NUM> is in contact with the inner surface on the bottom wall of the motor housing <NUM>, and the front surface on the front end of the sliding part <NUM> contacts the rear end of the linkage part <NUM>. The sliding part <NUM> has a rear end <NUM>, a grip part <NUM>, an engaging part <NUM>, a protruding part <NUM>, and a flat part <NUM>. The rear end <NUM> forms the rear end of the sliding part <NUM> and has a pawl part that extends in the front-rear direction so as to be insertable in the through-hole 2211a. The grip part <NUM> is positioned in the center of the sliding part <NUM> relative to the front-rear direction. The grip part <NUM> protrudes downward from the bottom surface of the sliding part <NUM>. The engaging part <NUM> has an L-shape in a side view. The engaging part <NUM> is disposed in the same position as the grip part <NUM> relative to the front-rear direction and extends upward from the top surface of the sliding part <NUM>. A pawl part capable of engaging with the engaging part <NUM> is provided on the distal end of the engaging part <NUM>. The protruding part <NUM> has a rectangular shape in a side view. The protruding part <NUM> is disposed at the same position as the push button 211a relative to the front-rear direction. The protruding part <NUM> extends upward from the top surface of the sliding part <NUM>. The top surface of the protruding part <NUM> confronts the bottom surface of the push button 211a. The flat part <NUM> has a flat plate shape. The flat part <NUM> is disposed at a position below the motor housing <NUM> and extends along the front-rear direction substantially parallel to the motor housing <NUM>. The portion of the bottom wall constituting the sliding part <NUM> that is positioned below the on-lock lever <NUM> slopes upward toward the rear. A through-hole <NUM> is formed in this sloped surface, penetrating the wall portion vertically. When the operator applies upward force to the bottom surface of the flat part <NUM>, the sliding part <NUM> can pivot about a rotational axis (not shown) positioned at the front end of the sliding part <NUM>. When the sliding part <NUM> is slid in the front-rear direction, the sliding part <NUM> pushes the linkage part <NUM> forward. Further, the bottom end of the intermediate part <NUM> connected to the front end of the linkage part <NUM> moves substantially forward inside the motor housing <NUM>.

Next, operations of the disc grinder <NUM> according to the third embodiment and operations of the on-lock lever <NUM> and sliding part <NUM> will be described with reference to <FIG>.

To operate the disc grinder <NUM>, the operator supports the sliding part <NUM> around the flat part <NUM> or the gear cover with one hand and grips the grip part <NUM> of the sliding part <NUM> with the other hand. The state of the disc grinder <NUM> shown in <FIG> is the state in which no external force is being applied to the sliding part <NUM> and on-lock lever <NUM> and neither of the sliding part <NUM> and on-lock lever <NUM> is being operated. In this state, the sliding part <NUM> is halted in the rearmost position of its slidable range by the urging force of the spring <NUM>. At this time, the pawl part of the rear end <NUM> is inserted into the through-hole 2211a, and the rear surface of the rear end <NUM> is in contact with the front surface of the wall part <NUM>. The lever part <NUM> of the on-lock lever <NUM> is also halted in its rightmost position within its pivotable range by the urging force of the torsion spring <NUM> in the C2 direction (<FIG>). The position of the on-lock lever <NUM> at this time will be called the on-lock release position. The engaging part <NUM> and engaging part <NUM> are not engaged at this time.

Even if the operator were to apply force to the sliding part <NUM> in the B1 direction while neither of the sliding part <NUM> and on-lock lever <NUM> is being operated (<FIG>), the pawl part of the rear end <NUM> is configured to contact the inner circumferential surface forming the through-hole 2211a so that the flat part <NUM> cannot pivot more than a prescribed angle. Accordingly, the protruding part <NUM> does not press against the push button 211a that serves to drive the motor <NUM>. The position of the sliding part <NUM> at this time will be called the off-lock position. Further, the position of the sliding part <NUM> when the flat part <NUM> is in the position shown in <FIG> and the protruding part <NUM> is not pressed against the push button 211a will be called the OFF position. When the sliding part <NUM> is in the OFF position, an internal space <NUM> is formed at the same position as the through-hole <NUM> in the front-rear direction and inside of the outer circumferential surface of the sliding part <NUM> (<FIG>).

When the sliding part <NUM> is in the OFF position as shown in <FIG>, the entire lever part <NUM> of the on-lock lever <NUM> is accommodated in the internal space <NUM> (the housing <NUM>). An external force cannot easily be applied to the lever part <NUM> of the on-lock lever <NUM> at this time since the lever part <NUM> is accommodated in the internal space <NUM>. Hence, the operator is prevented from operating the on-lock lever <NUM> and enabling the off-lock prior to operating the sliding part <NUM>.

When the operator applies force to the grip part <NUM> of the sliding part <NUM> in the A1 direction shown in <FIG> to slide the grip part <NUM> forward, the entire pawl part of the rear end <NUM> that was inserted into the through-hole 2211a becomes exposed to the outside. As a result, the pawl part of the rear end <NUM> no longer vertically opposes the inner circumferential surface defining the through-hole 2211a, forming a prescribed vertical gap between the pawl part and the bottom surface of the tail cover <NUM>, thereby enabling the flat part <NUM> to pivot in the B1 direction. The position of the sliding part <NUM> shown in <FIG> when the pawl part of the rear end <NUM> and the flat part <NUM> are allowed to pivot in the B1 direction will be called the off-lock release position. At this time, no external force is being applied to the on-lock lever <NUM>, and the on-lock lever <NUM> remains in the initial position. However, since the through-hole <NUM> formed in the sloped surface on the bottom wall of the sliding part <NUM> moves forward relative to the lever part <NUM> of the on-lock lever <NUM>, the distal end of the lever part <NUM> protrudes slightly out from the through-hole <NUM>. In other words, the amount that the lever part <NUM> protrudes from the tail cover <NUM> in the disc grinder <NUM> is smaller when the sliding part <NUM> is in the off-lock position than when the sliding part <NUM> is in the off-lock release position. Therefore, this configuration suppresses the operator from unintentionally placing the sliding part <NUM> in the ON position when the sliding part <NUM> is in the off-lock position, thereby further enhancing usability. When the sliding part <NUM> of the disc grinder <NUM> is in the off-lock release position and the on-lock lever <NUM> is in the on-lock release position, the sliding part <NUM> can pivot in the B1 direction.

In the state of <FIG>, when the operator applies force to the sliding part <NUM> in the B1 direction while continuing to exert force on the grip part <NUM> of the sliding part <NUM> to maintain the sliding part <NUM> in the off-lock release position, the sliding part <NUM> pivots in the B1 direction about the distal end of the sliding part <NUM>. Since no external force is being applied to the on-lock lever <NUM> at this time, the on-lock lever <NUM> remains in the initial position. The protruding part <NUM> provided on the sliding part <NUM> moves upward as the sliding part <NUM> pivots in the B1 direction and presses against the push button 211a of the switch <NUM> to turn the switch <NUM> on. Accordingly, power is supplied from the external power supply to the motor <NUM> via the power cord <NUM>, driving the motor <NUM> (<FIG>). The position of the sliding part <NUM> when the flat part <NUM> is in the position shown in <FIG> and the switch <NUM> has been switched on by the protruding part <NUM> will be called the ON position.

When the operator pivots the sliding part <NUM> in the B1 direction, the remaining portion of the lever part <NUM> on the on-lock lever <NUM> accommodated in the internal space <NUM> protrudes out through the through-hole <NUM> of the sliding part <NUM> as the sliding part <NUM> pivots. Accordingly, the operator can operate the lever part <NUM> (<FIG>).

If the operator pivots the lever part <NUM> about the rotational axis of the support part <NUM> for the on-lock lever <NUM> so that the lever part <NUM> moves substantially forward relative to the sliding part <NUM> along the C1 direction in <FIG> (clockwise) while the sliding part <NUM> is maintained in the ON position shown in <FIG>, the engaging part <NUM> moves substantially rearward to become positioned beneath the pawl part of the engaging part <NUM> (<FIG>). When the operator gradually lessens the gripping force on the flat part <NUM> while holding the lever part <NUM> with a finger against the urging force of the torsion spring <NUM> so that the front surface of the lever part <NUM> contacts the inner circumferential surface forming the through-hole <NUM>, the sliding part <NUM> pivots by its own weight in the B2 direction (clockwise) about a rotational axis (not shown). Accordingly, the pawl part of the engaging part <NUM> provided on the sliding part <NUM> moves downward and engages with the pawl part of the engaging part <NUM> (<FIG>). At this time, the magnitude of the weight of the sliding part <NUM> urging the sliding part <NUM> in the B2 direction to lower the engaging part <NUM> provided on the sliding part <NUM> side is greater than the urging force of the torsion spring <NUM> that urges the engaging part <NUM> in the C2 direction. Consequently, even if the operator releases the lever part <NUM> of the on-lock lever <NUM>, the engagement between the engaging part <NUM> and engaging part <NUM> is maintained while the front surface of the lever part <NUM> maintains contact with the inner circumferential surface forming the through-hole <NUM>. Hence, the pawl part of the engaging part <NUM> and the pawl part of the engaging part <NUM> do not disengage unless a prescribed external force is applied. The contact between the front surface of the lever part <NUM> and the inner circumferential surface forming the through-hole <NUM> owing to the engagement between the pawl part on the engaging part <NUM> of the on-lock lever <NUM> supported in the tail cover <NUM> and the pawl part on the engaging part <NUM> of the sliding part <NUM> stops the sliding part <NUM> from sliding in the A2 direction and pivoting in the B2 direction. The sliding part <NUM> is maintained in the ON position even if the operator releases the sliding part <NUM> at this time, and the motor <NUM> continues driving. The position of the on-lock lever <NUM> in this state will be called the on-lock position. At this time, the motor <NUM> is driving while operations of the on-lock lever <NUM> and sliding part <NUM> are both halted. This state will be called the on-lock state of the disc grinder <NUM>.

Next, the operations performed when halting operation of the disc grinder <NUM> will be described. When the disc grinder <NUM> is in the on-lock state (<FIG>) and the operator grips the sliding part <NUM> and applies force to the flat part <NUM> in the B1 direction, the engaging part <NUM> provided on the sliding part <NUM> moves upward relative to the on-lock lever <NUM>. Hence, the pawl part of the engaging part <NUM> separates from the pawl part of the engaging part <NUM>, disengaging the two (<FIG>). Consequently, the urging force of the torsion spring <NUM> pivots the lever part <NUM> of the on-lock lever <NUM> in the C2 direction. The lever part <NUM> pivots toward the on-lock release position and stops at the rightmost position within its pivotable range (<FIG>). By releasing the engagement between the pawl part of the engaging part <NUM> and the pawl part of the engaging part <NUM>, the sliding part <NUM> can pivot in the B2 direction. When the operator releases the sliding part <NUM>, the sliding part <NUM> pivots further in the B2 direction by its weight and stops moving in the OFF position (<FIG>). At the same time, the grip part <NUM> of the sliding part <NUM> is slid in the A2 direction by the urging force of the spring <NUM>, and the pawl part of the rear end <NUM> is inserted into the through-hole 2211a. The grip part <NUM> comes to a halt at the rearmost position within its slidable range. The top surface of the protruding part <NUM> also moves in a direction away from the push button 211a as the sliding part <NUM> pivots in the B2 direction. When the protruding part <NUM> has moved a prescribed distance in the direction away from the push button 211a, i.e., when the separated distance reaches a prescribed magnitude, power supplied from the external power supply to the motor <NUM> via the power cord <NUM> is stopped, and the motor <NUM> stops driving. At this time, the drive of the motor <NUM> and operations of the sliding part <NUM> and on-lock lever <NUM> are halted (<FIG>). Note that the disc grinder according to the third embodiment of the present invention is merely an example of the power tool in the invention and is not limited to the embodiment described above. Various modifications and improvements may be made therein without departing from the spirit of the invention, the scope of which is defined by the attached claims. The third embodiment described above differs from the first and second embodiments in the timing at which the on-lock lever is exposed. Specifically, while the on-lock lever is exposed when the switch lever is moved to the ON position in the first and second embodiments, the on-lock lever <NUM> in the third embodiment is exposed when the off-lock is released. Since the on-lock lever <NUM> in this configuration is not exposed during the initial state prior to the off-lock being released, this configuration suppresses the operator from applying force to the on-lock lever <NUM> before turning on the motor <NUM>, thereby suppressing the operator from placing the disc grinder <NUM> in the on-lock state unintentionally.

Next, a disc grinder <NUM> will be described as an example of the power tool according to a fourth embodiment of the present invention while referring to <FIG>. The disc grinder <NUM> has essentially the same structure as the disc grinder <NUM> according to the second embodiment. Components identical to those in the disc grinder <NUM> are designated with the same reference numerals to avoid duplicating description. The following description will primarily cover different structures and structures that need to be described in greater detail. Structures identical to those of the disc grinder <NUM> obtain the same effects as described above.

As shown in <FIG>, the disc grinder <NUM> according to the fourth embodiment is provided with a tail cover <NUM> in place of the tail cover <NUM>. The tail cover <NUM> differs from the tail cover <NUM> in that a through-hole <NUM> extending vertically is formed in the top surface of the tail cover <NUM> at a position to the rear of the motor <NUM>. The disc grinder <NUM> according to the fourth embodiment is also provided with a switch lever part <NUM> in place of the switch lever part <NUM>. The switch lever part <NUM> extends along the front-rear direction parallel to the motor housing <NUM> and the tail cover <NUM>. An engaging part <NUM> is provided on the top surface of the switch lever part <NUM> in place of the engaging part <NUM>. The engaging part <NUM> extends upward from the surface of the switch lever part <NUM> at a position to the rear of the first protruding part <NUM>. A pawl part having an L-shape in a side view is provided on the distal end of the engaging part <NUM>. The disc grinder <NUM> according to the fourth embodiment is also provided with an on-lock part <NUM> in place of the on-lock lever <NUM>.

As shown in <FIG>, the on-lock part <NUM> has a sliding part <NUM>, an intermediate part <NUM>, and a spring <NUM>. The sliding part <NUM> is supported in the tail cover <NUM> so as to be capable of sliding in the front-rear direction. The rear end of the sliding part <NUM> is connected to the top end of the intermediate part <NUM>. The sliding part <NUM> has a protrusion by which the operator operates the sliding part <NUM>. The protrusion of the sliding part <NUM> protrudes upward through the through-hole <NUM>. The spring <NUM> extends in the front-rear direction and is disposed below the through-hole <NUM> and at a position in the front-rear direction between the sliding part <NUM> and the inner wall of the tail cover <NUM>. The spring <NUM> urges the sliding part <NUM> rearward. The intermediate part <NUM> has a support part <NUM>, and an engaging part <NUM>. The support part <NUM> is positioned in the center portion of the intermediate part <NUM> relative to the vertical direction. The intermediate part <NUM> is pivotably supported in the tail cover <NUM> via a rotational shaft inserted through a through-hole formed in the support part <NUM>. The engaging part <NUM> is provided on the bottom end of the intermediate part <NUM>. The engaging part <NUM> has a pawl part capable of engaging with the engaging part <NUM>. In the disc grinder <NUM> according to the fourth embodiment, the on-lock part <NUM> is disposed on a side of the motor <NUM> radially opposite that of the off-lock part <NUM>. In other words, the on-lock part <NUM> is positioned on one side (top) of the rotational shaft of the motor <NUM>, while the off-lock part <NUM> is disposed on the other side (bottom). This arrangement prevents the operator from confusing operations of the on-lock part <NUM> and off-lock part <NUM>, thereby further enhancing usability.

Next, operations of the disc grinder <NUM> according to the fourth embodiment and operations of the on-lock part <NUM> and off-lock part <NUM> will be described with reference to <FIG>.

To operate the disc grinder <NUM>, the operator grips the flat part <NUM> of the switch lever part <NUM> with one hand and grips the lever part <NUM> of the off-lock part <NUM> with the other hand. The state of the disc grinder <NUM> shown in <FIG> is the state in which no external force is being applied to the switch lever part <NUM>, on-lock part <NUM>, and off-lock part <NUM> and none of the switch lever part <NUM>, on-lock part <NUM>, and off-lock part <NUM> is being operated. In this state, the lever part <NUM> of the off-lock part <NUM> is halted in the rearmost position within its slidable range by the urging force of the spring <NUM>. At this time, the top surface of the protrusion on the third protruding part <NUM> vertically opposes the bottom surface of the anchoring part <NUM> on the tail cover <NUM> at a prescribed distance. In this initial state, the spring <NUM> also urges the switch lever part <NUM> substantially downward relative to the tail cover <NUM> along the B2 direction (<FIG>) and is halted in the lowermost position within the pivotable range of the switch lever part <NUM>. The sliding part <NUM> of the on-lock part <NUM> is also halted in the rearmost position of its slidable range by the urging force of the spring <NUM> in the C1 direction (<FIG>). The position of the on-lock part <NUM> at this time will be called the on-lock release position. The engaging part <NUM> and the engaging part <NUM> are not engaged at this time.

Even if the operator were to apply a force to the flat part <NUM> of the switch lever part <NUM> in the B1 direction shown in <FIG> while none of the switch lever part <NUM>, on-lock part <NUM>, and off-lock part <NUM> is being operated, the top surface of the protrusion on the third protruding part <NUM> is configured to contact the bottom surface of the anchoring part <NUM>, preventing the flat part <NUM> from pivoting more than a prescribed angle. Accordingly, the second protruding part <NUM> does not press against the push button 211a that serves to drive the motor <NUM>. The position of the off-lock part <NUM> at this time will be called the off-lock position. Further, the position of the switch lever part <NUM> when the flat part <NUM> is in the position shown in <FIG> and the second protruding part <NUM> is not pressing against the push button 211a will be called the OFF position.

When the operator applies force to the lever part <NUM> of the off-lock part <NUM> in the A1 direction of <FIG> to slide the lever part <NUM> forward, the third protruding part <NUM> provided on the lever part <NUM> slides forward relative to the anchoring part <NUM>. As a result, the top end of the third protruding part <NUM> no longer confronts the anchoring part <NUM> vertically, and the flat part <NUM> can pivot in the B1 direction. At this time, the switch lever part <NUM> and on-lock part <NUM> remain in their initial positions while no force is applied to the same. The position of the off-lock part <NUM> shown in <FIG> when the top end of the third protruding part <NUM> no longer opposes the anchoring part <NUM> vertically and the flat part <NUM> is allowed to pivot in the B1 direction will be called the off-lock release position. When the off-lock part <NUM> of the disc grinder <NUM> is in the off-lock release position and the on-lock part <NUM> is in the on-lock release position, the flat part <NUM> of the switch lever part <NUM> can pivot in the B1 direction.

In the state of <FIG>, when the operator applies force to the switch lever part <NUM> in the B1 direction while continuing to exert force on the lever part <NUM> of the off-lock part <NUM> against the urging force of the spring <NUM> in order to maintain the off-lock part <NUM> in the off-lock release position, the flat part <NUM> pivots in the B1 direction. At this time, no external force is being applied to the on-lock part <NUM>, and the on-lock part <NUM> remains in the initial position. The second protruding part <NUM> provided on the switch lever part <NUM> moves upward as the flat part <NUM> pivots in the B1 direction and presses against the push button 211a of the switch <NUM>. Accordingly, power is supplied from the external power supply to the motor <NUM> via the power cord <NUM>, driving the motor <NUM> (<FIG>). The position of the switch lever part <NUM> when the flat part <NUM> is in the position shown in <FIG> and the second protruding part <NUM> is pressed against the push button 211a will be called the ON position.

When the operator slides the sliding part <NUM> of the on-lock part <NUM> in the C1 direction (forward) of <FIG> while the switch lever part <NUM> is maintained in the ON position shown in <FIG>, the engaging part <NUM> of the intermediate part <NUM> connected to the rear end of the sliding part <NUM> pivots in a D2 direction (<FIG>) about the rotational axis of the support part <NUM>. As a result, the engaging part <NUM> provided on the intermediate part <NUM> moves substantially rearward to become positioned beneath the pawl part of the engaging part <NUM>. At this time, the top surface of the protrusion on the third protruding part <NUM> is positioned higher than the bottom surface of the anchoring part <NUM>, and the protrusion on the third protruding part <NUM> is positioned forward of the anchoring part <NUM> by a prescribed distance. If the operator gradually lessens the gripping force on the flat part <NUM> while holding the sliding part <NUM> with a finger against the urging force of the spring <NUM> to maintain the sliding part <NUM> in the frontmost position of its slidable range, the switch lever part <NUM> is pivoted in the B2 direction (clockwise) about a rotational axis (not shown) by the urging force of the spring <NUM>. Accordingly, the pawl part of the engaging part <NUM> provided on the switch lever part <NUM> moves downward and engages with the pawl part on the engaging part <NUM> (<FIG>). At this time, the urging force of the spring <NUM> that urges the switch lever part <NUM> in the B2 direction to lower the engaging part <NUM> provided on the switch lever part <NUM> side is greater than the urging force of the spring <NUM> that urges the engaging part <NUM> substantially forward relative to the tail cover <NUM>. Consequently, even if the operator releases the sliding part <NUM> of the on-lock part <NUM>, the engagement between the engaging part <NUM> and engaging part <NUM> is maintained, i.e., the pawl part on the engaging part <NUM> and the pawl part on the engaging part <NUM> do not disengage unless a prescribed force is applied. The switch lever part <NUM> is stopped from pivoting in the B2 direction by this engagement between the pawl part on the engaging part <NUM> of the on-lock part <NUM>, supported in the tail cover <NUM>, and the pawl part on the engaging part <NUM> of the switch lever part <NUM>. When the operator releases the lever part <NUM>, the rear surface of the protrusion on the third protruding part <NUM> contacts the front surface of the anchoring part <NUM> and stops the off-lock part <NUM> from sliding rearward at this time. Further, the switch lever part <NUM> is maintained in the ON position when the operator releases the switch lever part <NUM>, and the motor <NUM> continues driving. The position of the on-lock part <NUM> in this state will be called the on-lock position. At this time, the motor <NUM> is driving while operations of the switch lever part <NUM>, on-lock part <NUM> and off-lock part <NUM> are all halted. This state will be called the on-lock state of the disc grinder <NUM>.

Next, the operations performed when halting operation of the disc grinder <NUM> will be described. When the disc grinder <NUM> is in the on-lock state (<FIG>) and the operator grips the switch lever part <NUM> and applies force to the flat part <NUM> in the B1 direction, the engaging part <NUM> provided on the switch lever part <NUM> moves upward relative to the on-lock part <NUM>. Hence, the pawl part of the engaging part <NUM> separates from the pawl part of the engaging part <NUM>, disengaging the two (<FIG>). Consequently, the urging force of the spring <NUM> slides the sliding part <NUM> of the on-lock part <NUM> in the C2 direction. The sliding part <NUM> slides toward the on-lock release position and stops at the rearmost position within its slidable range (<FIG>). By releasing the engagement between the pawl part of the engaging part <NUM> and the pawl part of the engaging part <NUM>, the switch lever part <NUM> can pivot in the B2 direction. When the operator releases the switch lever part <NUM>, the switch lever part <NUM> pivots farther in the B2 direction owing to the urging force of the spring <NUM>, and movement of the switch lever part <NUM> is halted at the OFF position (<FIG>). Accordingly, the lever part <NUM> of the off-lock part <NUM> is slid in the A2 direction by the urging force of the spring <NUM> and comes to a halt in the rearmost position of its slidable range. The top surface of the second protruding part <NUM> also moves in a direction away from the push button 211a as the switch lever part <NUM> pivots in the B2 direction. When the second protruding part <NUM> has separated from the push button 211a by a prescribed distance, power supplied from the external power supply to the motor <NUM> via the power cord <NUM> is stopped, and the motor <NUM> stops driving. At this time, the drive of the motor <NUM> and operations of the switch lever part <NUM>, on-lock part <NUM>, and off-lock part <NUM> are all halted, placing the disc grinder <NUM> in its initial state (<FIG>). As described above, the fourth embodiment of the present invention enhances usability by arranging the on-lock part <NUM> forward from the off-lock part <NUM> while usability can be further enhanced by considering the arrangement of these parts.

Claim 1:
A working machine (<NUM>, <NUM>, <NUM>, <NUM>) comprising:
a housing (<NUM>);
a motor (<NUM>) accommodated in the housing;
an operating part (<NUM>, <NUM>, <NUM>, <NUM>) which is a part of the housing, the operating part being movable between an on position and an off position, the motor being driven when the operating part is in the on position, and the motor being stopped when the operating part is in the off position; and
an on-locking means (<NUM>, <NUM>, <NUM>, <NUM>) capable of maintaining the motor in a driving state;
wherein at least a portion of the on-locking means is not exposed prior to performing an operation to turn on the motor, and the portion of the on-locking means is exposed by performing the operation to turn on the motor such that the on-locking means becomes operable,
characterised in that:
the operating part (<NUM>, <NUM>, <NUM>, <NUM>) has a shielding part (<NUM>, <NUM>, <NUM>);
wherein the shielding part (<NUM> , <NUM>, <NUM>) is provided on an outer peripheral wall of the housing so as to form an internal space (<NUM>) between the shielding part (<NUM>, <NUM>, <NUM>) and the housing (<NUM>);
wherein an entire part (<NUM>) of the on-locking means is positioned in the internal space when the operating part is in the off position,
or
wherein an amount that the on-locking means protrudes from the internal space when the operating part is in the on position is greater than an amount that the on-locking means protrudes from the internal space when the operating part is in the off position.