Patent Description:
At an entrance of a hazard area where an industrial machine such as an automatically operated machine tool is set on, a safety switch is provided that is switched on/off according to opening/closing state of a door.

For example, <CIT> discloses in <FIG> a safety switch (<NUM>), which includes a key (or actuator) (<NUM>) disposed on the door side, a headpiece housing (<NUM>) disposed on the wall side and having a keyway (or actuator insertion hole) (<NUM>), and a housing (<NUM>). Inside the headpiece housing (<NUM>), a wheel with a notch (or cam) (<NUM>) is provided that is rotatable forwardly and reversely according to insertion/extraction of the key (<NUM>) into/from the keyway (<NUM>). Inside the housing (<NUM>), there are provided a reciprocatable plunger (<NUM>) that engages with a rest notch (<NUM>) of the wheel (<NUM>) in a rotational position at the time of door closing to lock the wheel (<NUM>) and a switch (<NUM>) that switches contacts according to motion of the plunger (<NUM>).

In such a safety switch, as the door closes, the key (<NUM>) is inserted into the keyway (<NUM>) to rotate the wheel (<NUM>) and a distal end portion of the spring-biased plunger (<NUM>) engages with the rest notch (<NUM>) of the wheel (<NUM>) to lock the wheel (<NUM>). As a result, the contacts of the switch (<NUM>) are switched from OFF to ON, so that the machine is powered on. At this time, since the wheel (<NUM>) is locked, an operator is prevented from opening the door during operation of the machine and he/she is thus prevented an access to the hazard area. On the other hand, when a stator (<NUM>) around the plunger (<NUM>) is energized in a lock state of the wheel (<NUM>), the distal end portion of the plunger (<NUM>) is extracted from the rest notch (<NUM>) of the wheel (<NUM>) and the plunger (<NUM>) moves backward. As a result, the lock state of the wheel (<NUM>) is released and unlocked, and thus the operator can open the door. At this time, the machine is powered off and its operation is stopped.

In the safety switch shown in <CIT> , a semi-circular distal end portion of the plunger (<NUM>) is merely engaged with a semi-circular rest notch (<NUM>) of the wheel (<NUM>) in order to lock the wheel (<NUM>), which lacks in stability as a lock state.

Therefore, a safety switch is proposed that has a lock member provided discretely from a plunger. For example, a safety switch shown in <FIG> of <CIT> includes a swingable lock lever (<NUM>) that is engageable with a locking step (1d) formed on an outer circumferential surface of the drive cam (<NUM>). A distal engagement piece (50a) of the lock lever (<NUM>) is elastically biased toward the outer circumferential surface of the drive dam (<NUM>) by a spring force.

When the drive cam (<NUM>) is rotationally moved to a lock position by insertion of the actuator (<NUM>), the engagement piece (50a) of the lock lever (<NUM>) moves radially inwardly from the outer circumferential surface of the drive cam (<NUM>) and engages with the locking step (1d) to lock the drive cam (<NUM>) (see para. On the other hand, when a solenoid structural part (<NUM>) (see <FIG>) is energized in a lock state of the drive cam (<NUM>), the plunger (90a) is retracted and the engagement piece (50a) of the lock lever (<NUM>) moves radially outwardly from the drive cam (<NUM>) and is thus disengaged from the locking step (1d). As a result, the lock state of the drive cam (<NUM>) is released and unlocked (see para.

In either of the above-mentioned safety switches, during the process of the locking motion of the wheel (<NUM>) and the drive cam (<NUM>), a reaction of the door at the time of its closing causes the door to move slightly toward an opening side. As a result of this, a state will occur in which the distal end portion of the plunger (<NUM>) is not fully engaged with the rest notch (<NUM>) of the wheel (<NUM>), or the engagement piece (50a) of the lock lever (<NUM>) is not fully engaged with the locking step (1d) of the drive cam (<NUM>). Also, during the process of the unlocking motion of the wheel (<NUM>) and the drive cam (<NUM>), as the door moves slightly toward the opening side, a state will occur in which the distal end portion of the plunger (<NUM>) is not fully disengaged from the rest notch (<NUM>) of the wheel (<NUM>), or the engagement piece (50a) of the lock lever (<NUM>) is not fully disengaged from the locking step (1d) of the drive cam (<NUM>).

At this moment, the distal end portion of the plunger (<NUM>) is inserted halfway through the rest notch (<NUM>) of the wheel (<NUM>) and is balanced with a friction force. Similarly, the engagement piece (50a) of the lock lever (<NUM>) is inserted halfway through the locking step (1d) of the drive cam (<NUM>) and is balanced with a friction force. Here, in the case that a plurality of lock contacts are provided, since ON/OFF switching timing of the respective contacts differ from each other, there is a possibility that incoincidence of the contacts occurs in a balance with the friction force. Since the machine regards such incoincidence as malfunction, each time incoincidence of the contacts frequently occurs, the machine stops, which decreases working efficiency.

The present invention has been made in view of these circumstances and its object is to prevent incoincidence of contacts from occurring in a safety switch. Other objects and advantages of the present invention will be obvious and appear hereinafter.

According to the present invention, by inserting the actuator into the switch body, the cam rotates and operating part switches the contact according to rotation of the cam.

At the time of locking motion of the cam, the locking part is going to move to the lock position. At this time, when the actuator moves in the drawing-out direction in the intermediate position between the unlock position and the lock position and the cam comes into contact with the cam contact surface of the locking part, it is only a part of an area with the protrusion that protrudes toward the cam on the cam contact surface of the locking part. An area other than the protrusion on the cam contact surface does not protrude toward the cam. Thereby, the locking part can smoothly pass the intermediate position between the unlock position and the lock position in the course of locking motion. As a result, the locking part can be prevented from being stopped by the friction with the cam in the middle of moving to the lock position and incoincidence of contacts can thus be prevented from occurring.

Also, at the time of unlocking motion of the cam, the locking part is going to move to the unlock position. At this time, when the actuator moves in the drawing-out direction in the intermediate position between the lock position and the unlock position and the cam comes into contact with the cam contact surface of the locking part, it is only a part of the area with the protrusion that protrudes toward the cam on the cam contact surface of the locking part. An area other than the protrusion on the cam contact surface does not protrude toward the cam. Thereby, the locking part can smoothly pass the intermediate position between the lock position and the unlock position in the course of unlocking motion. As a result, the locking part can be prevented from being stopped by the friction with the cam in the middle of moving to the unlock position and incoincidence of contacts can thus be prevented from occurring.

The bulge has a first planar surface and a second planar surface that intersect each other.

The locking part may be supported rotatably and a distance from a rotational center of the locking part to the first and second planar surfaces may be set such that the distance from the rotational center of the locking part to a boundary between the first and second planar surfaces is maximized.

The bulge may have an arcuate surface formed of a single or a plurality of arcs.

The cam may have a convex portion and the bulge of the locking part may travel while abutting on the convex portion as the locking part moves through the intermediate position between the lock position and the unlock position.

The locking part may be elastically supported through a gap that is adapted to absorb an interference with the convex portion of the cam.

The locking part may be rotatably supported and its supporting axis may be elastically supported through a radial gap.

As above-mentioned, according to the present invention, incoincidence of the contacts in the safety switch can be prevented from occurring.

The present invention will now be described in detail with reference to embodiments thereof as illustrated in the accompanying drawings. Referring to the drawings, <FIG> show a safety switch according to an embodiment of the present invention. In these drawings, <FIG> illustrate an external appearance of the safety switch. <FIG> illustrate an internal structure of the safety switch, whose sectional area is colored in gray. <FIG> illustrate an external appearance or a sectional shape of a locking lever. <FIG> are internal structural drawings or the detailed views for explaining the motion of the safety switch.

As shown in <FIG> , the safety switch <NUM> includes a switch body <NUM> disposed at a wall or a fixed door (not shown) for instance, and an actuator <NUM> disposed at a movable door for instance (not shown) and provided insertable and extractable relative to the switch body <NUM>. The safety switch <NUM> is structured in such a way as to switch contacts inside the switch body <NUM> in cooperation with the actuator <NUM> and the switch body <NUM>.

The switch body <NUM> has a head portion <NUM> on one end side. The head portion <NUM> has one or a plurality of (in this example, two) actuator insertion openings 20a, 20b into which a distal end portion <NUM> of the actuator <NUM> is inserted.

As shown in <FIG> (especially, <FIG>), the safety switch <NUM> has an operating cam <NUM> and a pair of locking cams <NUM> disposed on axially opposite sides of the operating cam <NUM> inside the head portion <NUM>. Both of the cams <NUM>, <NUM> are plate cams, which are rotatably supported by an axis <NUM> provided inside the head portion <NUM>. On axially external sides of the locking cams <NUM>, a pair of cam supporting portions <NUM> are disposed to support each of the locking cams <NUM> from its side. The axis <NUM> extends to sidewalls of the head portion <NUM> through the cam supporting portions <NUM>.

The operating cam <NUM>, shown in <FIG>, has a guide opening 21a that extends through the operating cam <NUM> in the thickness direction and that extends along the circumferential direction. Similarly, each of the locking cams <NUM>, shown in <FIG>, has a guide opening 22a that extends through the locking cam <NUM> in the thickness direction and that extends along the circumferential direction. The guide opening 22a is disposed at a position that corresponds to the guide opening 21a. An axially extending pin <NUM> is inserted into each of the guide openings 21a and 22a. Both ends of the pin <NUM> are supported by each of the cam supporting portions <NUM> ( <FIG>) and biased toward an inner circumferential side of each of the guide openings 21a and 22a by a spring (not shown) provided at each of the cam supporting portions <NUM>. According to this constitution, the operating cam <NUM> and each of the locking cams <NUM> are rotatable only in the state that the rotation angles coincide with each other.

On the outer circumferential surface of the operating cam <NUM>, shown in <FIG> , two notches 21c are formed and on the outer circumferential surface of each of the locking cams <NUM>, shown in <FIG> , two notches 22c are formed that respectively correspond to each of the notches 21c of the operating cam <NUM>. Prior to insertion of the distal end portion <NUM> of the actuator <NUM> deeply into the head portion <NUM> (see <FIG> and <FIG>), one of the notches 21c and the corresponding notch 22c are disposed in the vicinity of the actuator insertion opening 20a of the head portion <NUM>, and the other of the notches 21c and the corresponding notch 22c are disposed in the vicinity of the other actuator insertion opening 20b of the head portion <NUM>. The bifurcated distal end portion <NUM> of the actuator <NUM> inserted through the actuator insertion opening 20a (or 20b) of the head portion <NUM> has a press bar 30a at its distal end that comes into contact with a wall surface of each of the notches 21c, 22c of the operating cam <NUM> and each of the locking cams <NUM> to rotate both of the operating cam <NUM> and the locking cams <NUM>.

Inside the switch body <NUM>, shown in <FIG>, an operating rod (or an operating part) <NUM> is disposed extending in a longitudinal direction of the switch body <NUM>. A distal end of the operating rod <NUM> extends to the head portion <NUM> on one side of the switch body <NUM> and a rear end of the operating rod <NUM> extends toward the other side of the switch body <NUM>. The operating rod <NUM> is biased to the forwarding side toward the head portion <NUM> by a spring 26A and a convex arc surface 26a of the distal end of the operating rod <NUM> is in elastically contact with an outer circumferential surface 21b of the operating cam <NUM>. Thereby, at the time of rotation of the operating cam <NUM>, the operating rod <NUM> reciprocates with the distal end of the operating rod <NUM> following the motion of the outer circumferential surface 21b of the operating cam <NUM>. The rear end of the operating rod <NUM> is coupled to a contact block <NUM> provided on the other end side of the switch body <NUM>. Also, around a substantially central part of the operating rod <NUM>, a solenoid <NUM> is provided. The operating rod <NUM> is adapted to move rearwardly toward the opposite side end of the switch body <NUM>, that is, the distal end of the operating rod <NUM> is adapted to move away from the operating cam <NUM>, by energization of the solenoid <NUM>. The contact block <NUM> is provided with a lock contact and an unlock contact that switches contacts by turning on and off the contacts according to the movement of the operating rod <NUM>.

A locking lever (or locking part) <NUM> is disposed beside the distal end of the operating rod <NUM> inside the head portion <NUM>. As shown in <FIG>, the locking lever <NUM> includes a proximal portion 29b with a cylindrical supporting shaft 29a, a pair of lever portions 29d that extend in a bifurcated shape from the proximal portion 29b and that are coupled to each other through a thin plate portion 29c, and a semi-circular engagement recess 29c1 formed at a distal end of the thin plate portion 29c. The locking lever <NUM> is a member that extends from the proximal portion 29b to the distal end in an arc-shape (see <FIG> and <FIG>) and is downwardly convexly curved.

A distal end surface of each of the lever portions 29d, shown in <FIG> , has an upright first planar surface 29d1 and a second planar surface 29d2 that intersects the first planar surface 29d1 diagonally, such that thereby the distal end surface is formed in an angular shape. As shown in <FIG>, when drawing a circular arc C that has a center at a center O of the supporting shaft 29a and that has a radius of a distance R extending from the center O to a ridge line 29e which is a boundary between the first planar surface 29d1 and the second planar surface 29d2, both of the first and second planar surfaces 29d1, 29d2 are disposed inside the circular arc C. That is, regarding the distance from the center O to the first and second planar surfaces 29d1, 29d2, the distance R from the center O to the ridge line 29e, or a boundary between the first planar surface 29d1 and the second planar surface 29d2 is the greatest. Also, regarding a length of the first and second planar surfaces 29d1, 29d2 in the direction intersecting the ridge line 29e, the first planar surface 29d1 is longer than the second planar surface 29d2.

The supporting shaft 29a of the locking lever <NUM> is supported rotatably by the cam supporting portion <NUM> (<FIG>) in the head portion <NUM> and each of the lever portions 29d faces the corresponding locking cam <NUM> (see <FIG>). Thereby, the locking lever <NUM> is rotatable around a center axis line of the supporting shaft 29a and each of the lever portions 29d is thus movable toward and away from the locking cam <NUM>. The outer circumferential surface of each of the locking cams <NUM>, shown in <FIG> , has an engagement surface 22b formed thereon such that the distal end surface of each of the lever portions 29d comes into contact and engagement with the engagement surface 22b at the time of rotation of the locking lever <NUM>. Also, the engagement recess 29c1 of the locking lever <NUM>, shown in <FIG> , is in engagement with a circumferential groove 26b formed on the outer circumferential surface in the vicinity of the distal end of the operating rod <NUM>. Thereby, the locking lever <NUM> is rotatable according to the motion of the operating rod <NUM>.

In this manner, rotation of the locking lever <NUM> according to reciprocation (i.e. forward/rearward movement) of the operating rod <NUM> causes the locking lever <NUM> to be located at a lock position to lock rotation of the locking cam <NUM> and at an unlock position to unlock the lock state of the locking cam <NUM> (described in detail below).

Then, operation of the above-mentioned safety switch <NUM> will be explained. Here, first, operation when the actuator <NUM> is inserted into the head portion <NUM> of the switch body <NUM> at the time of closing the door will be explained in reference to <FIG>. In these drawings, coloring in gray or hatching to designate a sectional portion is omitted for illustration purposes.

As shown in <FIG>, <FIG> and <FIG> , the supporting shaft 29a of the locking lever <NUM> is housed via a radial gap e in an elongated hole 24a formed in the cam supporting portion <NUM> (<FIG>) and is biased at all times toward the side of the operating rod <NUM> that is one side of the elongated hole 24a. That is, the locking lever <NUM> is elastically supported via the gap e in the elongated hole 24a. At this time, a spring force by the spring 26A (<FIG> and <FIG>) always acts onto the operating rod <NUM>, which is always biased upwardly in the forward direction. Thereby, the locking lever <NUM> coupled to the operating rod <NUM> is biased at all times to rotate upwardly around the fulcrum O.

In <FIG>, <FIG> and <FIG> , the position of a wall surface of the circumferential groove 26b formed at the operating rod <NUM> designates a rotational position of the locking lever <NUM> and a contact state of the lock/unlock contacts in the contact block <NUM> (<FIG>), which are defined by the axial position of the operating rod <NUM> that reciprocates in the axial direction. In the drawings, "I" designates an unlock position of the locking lever <NUM>, "II" an ON/OFF switching point of the unlock contact, "III" an ON/OFF switching point of the lock contact, and "IV" a lock position of the locking lever <NUM>. Also, on the engagement surface 22b of the locking cam <NUM>, at a position near the outer circumferential surface of the locking cam <NUM>, there is formed a protrusion or protrusion (or a convex portion) 22d that has a semi-circular cross sectional shape and that extends along the engagement surface 22b into the page.

Operation No. (<NUM>) shown in <FIG> illustrates the state in which the actuator <NUM> is inserted into the actuator insertion opening 20a of the head portion <NUM> of the switch body <NUM> and the press bar 30a at the distal end of the actuator <NUM> causes the locking cam <NUM> to rotate in the counter-clockwise direction. In <FIG> showing the enlarged view of the locking lever <NUM> portion, the distal end of the locking lever <NUM> comes into contact with the protrusion 22d on the engagement surface 22b of the locking cam <NUM> from below and the locking lever <NUM> is located at the unlock position I (see the bold line in <FIG>) where the locking cam <NUM> is not locked. In the unlock position I, as shown in the table of <FIG> , the lock state of the locking cam <NUM> is turned "Unlock", the solenoid <NUM> (<FIG>) is turned "OFF", the lock contact is turned "OFF", and the unlock contact is turned "ON".

Operation No. (<NUM>) shown in <FIG> illustrates the state in which the locking cam <NUM> is further rotated from the state of the operation No. (<NUM>) in <FIG>. When the protrusion 22d on the engagement surface 22b of the locking cam <NUM> passes through a corner portion 29d0 on an upper side of the distal end of the locking lever <NUM> at the time of rotation of the locking cam <NUM>, the locking lever <NUM> rotates upwardly as shown in <FIG> because the locking lever <NUM> is biased upwardly around the fulcrum O. During rotation of the locking lever <NUM>, the first planar surface 29d1 at the distal end of the locking lever <NUM> slides along the protrusion 22d of the locking cam <NUM>. At this time, since the locking cam <NUM> is in the middle of rotation, a sliding resistance between the first planar surface 29d1 of the locking lever <NUM> and the protrusion 22d of the locking cam <NUM> is small and an upward rotation of the locking lever <NUM> is thus conducted smoothly. As a result, the locking lever <NUM> does not stop in the middle of the upward rotation of the locking lever <NUM> and thus the first planar surface 29d1 of the locking lever <NUM> is going to readily get over the protrusion 22d of the locking cam <NUM>.

In the state shown in <FIG> , the locking lever <NUM> is located at the ON/OFF switching point III of the lock contact (see the bold line in <FIG>). In the ON/OFF switching point III of the lock contact, as shown in the table of <FIG> , the lock state of the locking cam <NUM> is in the state of shifting from "Unlock to Lock", the solenoid <NUM> (<FIG>) is "OFF", the lock contact is in the state of shifting from "OFF to ON", and the unlock contact is turned "OFF".

Operation No. (<NUM>) shown in <FIG> illustrates the state in which the locking cam <NUM> is further rotated from the state of the operation No. (<NUM>) in <FIG> to come into contact with the press bar 30a of the actuator <NUM> and stops rotating. At this time, the first planar surface 29d1 of the locking lever <NUM>, shown in <FIG> , gets over the protrusion 22d of the locking cam <NUM> and moves to the position where the first planar surface 29d1 of the locking lever <NUM> faces the engagement surface 22b of the locking cam <NUM>.

In this state, the locking lever <NUM> is located at the lock position IV to lock the locking cam <NUM> (see the bold line in <FIG>). In the lock position IV, as shown in the table of <FIG> , the lock state of the locking cam <NUM> is turned "Lock", the solenoid <NUM> (<FIG>) is "OFF", the lock contact is turned "ON", and the unlock contact is "OFF".

Then, operation when the door bounds at the time of closing the door and the actuator <NUM> inserted into the head portion <NUM> is pulled in the drawing-out direction will be explained in reference to <FIG>. In these drawings, coloring in gray or hatching to designate a sectional portion is omitted for illustration purposes.

Operation No. (<NUM>) shown in <FIG> illustrates the state in which the actuator <NUM> moves in the drawing-out direction and stops after the locking cam <NUM> have been switched into the actuator intake side at the time of insertion of the actuator <NUM>. At this time, the solenoid <NUM> (<FIG>) is turned "ON" (see the table in <FIG>), and as shown in <FIG>, downward movement of the operating rod <NUM> causes the locking lever <NUM> to rotate downwardly. In this state, the locking lever <NUM> is located at the unlock position I (see the bold line in <FIG>), the lock state of the locking cam <NUM> is turned "Unlock", the lock contact is turned "OFF", and the unlock contact is turned "ON" (see the table in <FIG>).

As shown in <FIG>, a partially detailed view of <FIG>, when drawing a circular arc C1 that has a center at the rotational center O of the locking lever <NUM> and that is tangent to the protrusion 22d of the locking cam <NUM>, a radius R' of the circular arc C1 is smaller than the radius R ( <FIG>), i.e. R'<R. A triangular area 29f that includes the ridge line 29e on the distal end surface of the locking lever <NUM> and a portion of the first and second planar surfaces 29d1, 29d2 is a bulge that protrudes outside the circular arc C1.

Operation No. (<NUM>) shown in <FIG> illustrates the state immediately after the first planar surface 29d1 of the locking lever <NUM> comes into contact with the protrusion 22d of the locking cam <NUM> when the solenoid <NUM> (<FIG>) turns "OFF" from the state shown in <FIG> (see the table in <FIG>) and the operating rod <NUM> is moved upwardly by the spring force to cause the locking lever <NUM> to rotate upwardly. That is a switching point of mechanical lock/unlock of the locking cam <NUM>.

In this state, the locking lever <NUM> is located at a position in close proximity to the ON/OFF switching point II of the unlock contact (see the bold line in <FIG>). In the ON/OFF switching point II of the unlock contact, as shown in the table of <FIG> , the lock state of the locking cam <NUM> is in the state of shifting from "Unlock to Lock", the lock contact is "OFF", and the unlock contact is "ON".

As shown in <FIG> or a partially detailed view of <FIG>, in this case as well, similar to <FIG>, the bulge 29f that protrudes outside the circular arc C1 is formed of a triangular area that contains the ridge line 29e on the distal end surface of the locking lever <NUM> and a portion of the first and second planar surfaces 29d1, 29d2. The bulge 29f is an interference region that interferes with the protrusion 22d of the locking cam <NUM> while the locking lever <NUM> rotates further upwardly.

Operation No. (<NUM>) shown in <FIG> illustrates the state in which the locking lever <NUM> rotates further upwardly by slightly releasing the tense state of the actuator <NUM> in the draw-out direction from the state of the operation No. (<NUM>) in <FIG>. At the time of rotation of the locking lever <NUM>, as shown in <FIG>, the first planar surface 29d1 of the distal end of the locking lever <NUM> slides along the protrusion 22d of the locking cam <NUM> in contact with protrusion 22d. At this moment, since the supporting shaft 29a of the locking lever <NUM> is elastically supported in the elongated hole 24a via a gap, the locking lever <NUM> can move to the left in <FIG> thus absorbing interference of the protrusion 22d of the locking cam <NUM> with the bulge 29f (<FIG>) of the distal end of the locking lever <NUM>. In <FIG>, the gap e' after interference is smaller than the gap e, that is e'<e. Moreover, when the first planar surface 29d1 of the distal end of the locking lever <NUM> comes into contact with the protrusion 22d of the locking cam <NUM>, it is only a portion of an area with the bulge 29f that protrudes outside the circular arc C1 on the distal end surface of the locking lever <NUM>. An area other than the bulge 29f on the distal end surface of the locking lever <NUM> does not protrude outside circular arc C1. Thereby, rotation of the locking lever <NUM> in the upward direction can be conducted smoothly. As a result, the locking lever <NUM> does not stop halfway at the time of rotation in the upward direction and the first planar surface 29d1 of the distal end of the locking lever <NUM> is going to readily get over the protrusion 22d of the locking cam <NUM>.

In the state shown in <FIG> , the locking lever <NUM> is located at the ON/OFF switching point III of the lock contact (see the bold line in <FIG>). In the ON/OFF switching point III of the lock contact, as shown in the table of <FIG>, the lock state of the locking cam <NUM> is in the state of shifting from "Unlock to Lock", the solenoid <NUM> (<FIG>) is "OFF", the lock contact is in the state of shifting from "OFF to ON", and the unlock contact is turned "OFF".

Operation No. (<NUM>) shown in <FIG> illustrates the state in which the locking lever <NUM> rotates further upwardly from the state of the operation No. (<NUM>) in <FIG>. At this moment, as shown in <FIG> , the ridge line 29e at the distal end of the locking lever <NUM> run aground to the protrusion 22d of the locking cam <NUM> and the locking lever <NUM> moves further to the left thus absorbing interference with the protrusion 22d of the locking cam <NUM>. A gap e" after interference is smaller than the gap e', that is, e"<e'. Thereby, rotation of the locking lever <NUM> in the upward direction can be conducted in a smooth manner. As a result, the locking lever <NUM> does not stop halfway at the time of rotation in the upward direction and the ridge line 29e of the locking lever <NUM> is going to readily get over the protrusion 22d of the locking cam <NUM>.

In the state shown in <FIG>, the locking lever <NUM> is located immediately adjacent the lock position IV (see the bold line in <FIG>). In the lockposition VI, as shown in the table of <FIG> , the lock state of the locking cam <NUM> is in the state of shifting from "Unlock to Lock", the solenoid <NUM> (<FIG>) is "OFF", the lock contact is turned "ON", and the unlock contact is "OFF".

Operation No. (<NUM>) shown in <FIG> illustrates the state in which the locking lever <NUM> rotates further upwardly from the state of the operation No. (<NUM>) in <FIG>. At this moment, as shown in <FIG> , the first planar surface 29d1 of the distal end of the locking lever <NUM> engages with the engagement surface 22b of the locking cam <NUM> and the second planar surface 29d2 of the distal end of the locking lever <NUM> is disposed above the protrusion 22d of the locking cam <NUM>. Thereby, the distal end surface of the locking lever <NUM> is fitted into a concave portion formed above the protrusion 22d of the locking cam <NUM>.

In the state shown in <FIG> , the locking lever <NUM> is located at the lock position IV (see the bold line in <FIG>). In the lock position VI, as shown in the table of <FIG> , the lock state of the locking cam <NUM> is turned "Lock", the solenoid <NUM> (<FIG>) is "OFF", the lock contact is "ON", and the unlock contact is "OFF".

In such a manner, in the process of locking motion that shifts from the state of <FIG> through the state of <FIG>, <FIG> and <FIG> to the state of <FIG>, the locking lever <NUM> readily goes through the state of <FIG> , <FIG> and <FIG> to the state of <FIG> without stopping by a frictional force with the locking cam <NUM> in the state of <FIG> , <FIG> and <FIG>. Thereby, even in the case that a plurality of lock/unlock contacts are provided, it can be prevented that the state of being mixed with ON-state contacts and OFF-state contacts occurs and that incoincidence of the contacts occurs. As a result, a machine stop resulted from incoincidence of contacts can be prevented from occurring, thus improving work efficiency.

Then, operation will be explained in reference to <FIG> when the solenoid <NUM> (<FIG>) is turned "ON" with the locking lever <NUM> located at the lock position IV and the actuator <NUM> is pulled in the drawing-out direction. In these drawings, coloring in gray or hatching to designate a sectional portion is omitted for illustration purposes.

Operation No. (<NUM>) shown in <FIG> illustrates the state in which the actuator <NUM> is pulled in the drawing-out direction with the locking lever <NUM> located at the lock position. At this time, as shown in <FIG>, a pressing force from the engagement surface 22b of the locking cam <NUM> acts onto the distal end surface of the locking lever <NUM> with the distal end surface of the locking lever <NUM> fitted into the concave portion formed above the protrusion 22d of the locking cam <NUM>. As a result, the locking lever <NUM> moves to the left in <FIG> thus causing the gap e (<FIG>) between the supporting shaft 29a and the elongated hole 24a to be zero. At this moment, the locking lever <NUM> is completely locked between the engagement surface 22b of the locking cam <NUM> and the elongated hole 24a. Therefore, even if the solenoid <NUM> (<FIG>) is turned "ON" in this lock state, the locking lever <NUM> cannot rotate downwardly.

In the state shown in <FIG> , the locking lever <NUM> is located at the lock position IV (see the bold line in <FIG>). At this moment, as shown in the table of <FIG>, the lock state of the locking cam <NUM> is in the state of "Lock", the solenoid <NUM> (<FIG>) is "OFF", the lock contact is "ON", and the unlock contact is "OFF".

Operation No. (<NUM>) shown in <FIG> illustrates the state in which the solenoid <NUM> is turned "ON" from the state of the operation No. (<NUM>) in <FIG> and the locking lever <NUM> rotates downwardly by slightly loosening the tense state of the actuator <NUM> in the drawing-out direction. During the downward rotation of the locking lever <NUM>, shown in <FIG>, the second planar surface 29d2 of the distal end of the locking lever <NUM> gets over the protrusion 22d of the locking cam <NUM> and then the first planar surface 29d1 of the distal end of the locking lever <NUM> slides along the protrusion 22d with the first planar surface 29d1 running aground the protrusion 22d subsequently to the ridge line 29e.

At this time, as shown in <FIG> or a partially detailed view of <FIG>, when drawing a circular arc C having a center at the rotational center O of the locking lever <NUM> and a radius of a distance R from the center O to the ridge line 29e, both of the first and second planar surfaces 29d1, 29d2 are located inside the circular arc C and gradually separated away from the circular arc C as leaving the ridge line 29e. That is, when the locking lever <NUM> rotates around the rotational center O, the ridge line 29e is located at the position farthest from the rotational center O on the distal end surface of the locking lever <NUM> and it is the most prominent point on the distal end surface of the locking lever <NUM>. Therefore, as the downward rotational movement of the locking lever <NUM> advances further, interference of the first planar surface 29d1 of the locking lever <NUM> with the protrusion 22d is gradually reduced.

In the state shown in <FIG> , the locking lever <NUM> is located at an intermediate position between the ON/OFF switching point III of the lock contact and the lock position IV (see the bold line in <FIG>). At this moment, as shown in the table of <FIG> , the lock state of the locking cam <NUM> is "Lock", the solenoid <NUM> (<FIG>) is turned "ON", the lock contact is "ON", and the unlock contact is "OFF".

Operation No. (<NUM>) shown in <FIG> illustrates the state in which the locking lever <NUM> rotates further downwardly from the state of the operation No. (<NUM>) in <FIG>. During the rotation of the locking lever <NUM>, shown in <FIG> , the first planar surface 29d1 at the distal end of the locking lever <NUM> slides along the protrusion 22d of the locking cam <NUM> in contact with the protrusion 22d.

At this time, as above-mentioned, as the downward rotational movement of the locking lever <NUM> advances further, interference of the first planar surface 29d1 of the locking lever <NUM> with the protrusion 22d is gradually reduced and downward rotation of the locking lever <NUM> is thus conducted in a smooth manner. Thereby, the first planar surface 29d1 of the locking lever <NUM> is going to readily get over the protrusion 22d of the locking cam <NUM>.

In the state shown in <FIG> , the locking lever <NUM> is located at the ON/OFF switching point III (see the bold line in <FIG>). At this moment, as shown in the table of <FIG>, the lock state of the locking cam <NUM> is "Lock", the solenoid <NUM> (<FIG>) is "ON", the lock contact is in the state of shifting from "ON to OFF", and the unlock contact is "OFF".

Operation No. (<NUM>) shown in <FIG> illustrates the state in which the locking lever <NUM> rotates further downwardly from the state of the operation No. (<NUM>) in <FIG>. At this time, as shown in <FIG>, the first planar surface 29d1 at the distal end of the locking lever <NUM> is disengaged from the protrusion 22d of the locking cam <NUM> and the distal end surface of the locking lever <NUM> moves below the protrusion 22d of the locking cam <NUM>. Also, at this moment, the locking lever <NUM> moves to the right in <FIG> due to the spring force imparted by the spring <NUM> onto the supporting shaft 29a of the locking lever <NUM>. There is formed a gap e between the left-side opening end of the elongated hole 24a and the supporting shaft 29a.

In the state shown in <FIG>, the locking lever <NUM> is located at the unlock state I (see the bold line in <FIG>). At this moment, as shown in the table of <FIG>, the lock state of the locking cam <NUM> is turned "Unlock", the solenoid <NUM> (<FIG>) is "ON", the lock contact is turned "OFF", and the unlock contact is turned "ON". Also, in this state, even if the excitation of the solenoid <NUM> is released, since the protrusion 22d of the locking cam <NUM> is located above the distal end portion of the locking lever <NUM>, the locking lever <NUM> cannot rotate upwardly and thus the lock state of the locking cam <NUM> is not turned "Lock".

In such a fashion, in the process of unlock operation that shifts from the state of <FIG> through the state of <FIG> and <FIG> to the state of <FIG>, the locking lever <NUM> readily goes through the state of <FIG> and <FIG> to shift to the state of <FIG> without stopping due to the frictional force with the locking cam <NUM> in the state of <FIG> and <FIG>. Thereby, even in the case that a plurality of lock/unlock contacts are provided, it can be prevented that the state of being mixed with ON-state contacts and OFF-state contacts occurs and that incoincidence of the contacts occurs. As a result, a machine stop resulted from incoincidence of the contacts can be prevented, thus improving work efficiency.

In the above-mentioned embodiment, the bulge 29f provided on the distal end surface of the locking lever <NUM> is formed by the first and second planar surfaces 29d1, 29d2 that intersect each other.

In the above-mentioned embodiment, the protrusion 22d having a semicircular shape in cross section is formed at the engagement surface 22b of the locking cam <NUM>.

In the above-mentioned embodiment, an example was shown in which the supporting shaft 29a of the locking lever <NUM> is housed in the elongated hole 24a of the cam supporting portion <NUM> via the radial gap e, but application of the present invention is not limited to such an example. The present invention also has application to an example in which the supporting shaft 29a of the locking lever <NUM> may be housed in a circular hole formed in the cam supporting portion <NUM> without a radial gap.

In the above-mentioned embodiment, an example was shown in which the locking lever <NUM> as a locking part is provided rotatable around the center axis line of the supporting shaft 29a.

In the above-mentioned embodiment, an example was shown in which the cam according to the present invention is composed of the operating cam <NUM> and a pair of locking cams <NUM>, that is, the entire cam composed of the operating cam <NUM> and a pair of locking cams <NUM> is regarded as one cam assembly, but application of the present invention is not limited to such an example. For example, only the operating cam as a cam according to the present invention may be provided and the operation cam may be structured to have the function of the locking cam as well.

Claim 1:
A safety switch (<NUM>) that switches a contact by cooperation of an actuator (<NUM>) and a switch body (<NUM>), said switch body (<NUM>) comprising:
a cam (<NUM>, <NUM>) that is adapted to rotate by insertion of said actuator (<NUM>);
an operating part (<NUM>) that switches said contact according to rotation of said cam (<NUM>, <NUM>); and
a locking part (<NUM>) that is adapted to pass from a lock position in which it locks rotation of said cam (<NUM>, <NUM>) and an unlock position in which it unlocks a lock state of said cam (<NUM>, <NUM>) via an intermediate position between said lock position and said unlock position by actuation of said actuator (<NUM>);
characterised in that said locking cam (<NUM>) has a protrusion (22d) of a semi-circular cross sectional shape extending along an engagement surface (22b) of said cam (<NUM>, <NUM>) at a position near an outer circumferential surface of said cam (<NUM>, <NUM>), said locking part (<NUM>) is a locking lever (<NUM>) having a bulge (29f) at a portion of a cam contact surface of said locking lever (<NUM>), said bulge (29f) is protruded toward said cam (<NUM>, <NUM>) from a circular arc (C<NUM>) that has a center at a rotational center (O) of said locking lever (<NUM>) and that is tangent to said protrusion (22d) of said locking cam (<NUM>), said bulge (29f) is formed of a first planar surface (29d<NUM>) and a second planar surface (29d<NUM>) that intersect each other, and said bulge (29f) formed of said first and second planar surfaces (29d<NUM>, 29d<NUM>) is adapted to contact said cam (<NUM>, <NUM>) when said actuator (<NUM>) moves in a drawing-out direction in said intermediate position between said lock position and said unlock position, whereby said first planar surface (29d<NUM>) of said locking lever (<NUM>) at a distal end thereof slides along said protrusion (22d) of said locking cam (<NUM>).