Limit switch

A limit switch has a housing having an opening in a front surface of the housing, and a connection hole in which a lead wire is drawn made in a bottom surface of the housing, a switch main body fixed in the housing, a front surface of which is vertically partitioned into a plurality of stages, a pair of fixed contact terminals embedded at each of the stages, an operation shaft exposed from a ceiling surface of the switch main body, a contact that is opened and closed by driving the operation shaft in a shaft center direction, and a projection provided between the fixed contact terminals embedded at the stages of the front surface of the switch main body.

BACKGROUND

1. Technical Field

The present invention relates to a limit switch, particularly to a wiring structure of a lead wire connected to a fixed contact terminal of the limit switch.

2. Related Art

Conventionally, in the case that the lead wire is connected to the fixed contact terminal of the limit switch, as illustrated in FIG. 3 of Patent Document 1, four lead wires have been drawn through a connection hole (not illustrated) made in a bottom surface of base 1, and a crimped terminal provided at a leading end of the lead wire has been fixed to each of a pair of fixed contact terminals vertically provided at two stages using connection screw.Patent Document 1: Japanese Unexamined Patent Publication No. 2001-43774

SUMMARY

In the conventional limit switch, although work to connect the lead wires to the pair of fixed contact terminals at the lower stage is relatively easy to perform, it takes a lot of work to perform routing of the lead wire when the lead wire is connected to the pair of fixed contact terminals at the upper stage. Particularly, for the connection of the thick lead wire in a narrow space, it is necessary to fold the lead wire in a complicated way in order to connect the lead wire to the fixed contact terminal at a position different from the drawn position, which results in work efficiency being degraded.

One or more embodiments of the present invention provides a limit switch in which the connection of the lead wire is easily perform with good work efficiency.

In accordance with one or more embodiments of the present invention, a limit switch, in which a switch main body is fixed into a housing including an opening in a front surface of the housing, a connection hole in which a lead wire is drawn is made in a bottom surface of the housing, a front surface of the switch main body is vertically partitioned into a plurality of stages, a pair of fixed contact terminals is embedded at each stage, and a contact is opened and closed by driving an operation shaft exposed from a ceiling surface of the switch main body in a shaft center direction. In the limit switch, a projection is provided between the fixed contact terminals embedded at the stages of the front surface of the switch main body.

According to one or more embodiments of the present invention, because the wiring can be performed by routing the lead wire through the projection, the connection work is facilitated to improve the work efficiency. Additionally, the limit switch having an excellent insulating characteristic is obtained because the fixed contact terminals adjacent to each other are partitioned by the projection.

In accordance with one or more embodiments of the present invention, in the limit switch, an outer circumferential surface of the projection may include a shape along a wiring route of the lead wire.

According to one or more embodiments of the present invention, the work to connect the lead wire can more efficiently be performed.

In accordance with one or more embodiments of the present invention, in the limit switch, the fixed contact terminal located at an upper stage may be arranged so as to be pushed out toward a near side from the fixed contact terminal located at a lower stage.

According to one or more embodiments of the present invention, a step is generated between the upper and lower fixed contact terminals. Therefore, even if the lead wire is connected to the fixed contact terminal on the lower stage side, the lead wire connected to the fixed contact terminal on the lower stage side does not obstruct the connection work of the fixed contact terminal on the upper stage side, and the efficiency of the connection work is further improved.

In accordance with one or more embodiments of the present invention, in the limit switch, an insulating wall may be provided, the insulating wall projecting toward the near side from an edge on at least one of both side surfaces of the switch main body.

According to one or more embodiments of the present invention, the insulating characteristic is further improved because the insulating wall can prevent the lead wire from abutting directly on an inside surface of the housing.

In accordance with one or more embodiments of the present invention, in the limit switch, the lead wire in which a crimped terminal is provided at a leading end thereof may be connected to the fixed contact terminal by a connection screw.

According to one or more embodiments of the present invention, because the lead wire can be connected to the fixed contact terminal through the crimped terminal, advantageously the connection work can further be facilitated to improve the work efficiency.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described with reference toFIGS. 1 to 9. In embodiments of the invention, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid obscuring the invention.

As illustrated inFIGS. 1 to 3, in a limit switch according to a first embodiment, switch main body20assembled in housing10is driven by driving mechanism50including operation lever69through plunger40.

Housing10has a box shape in which switch main body20can be accommodated, and circular rib12is formed along opening11provided in a front surface of housing10. Circular seal member13is positioned in circular rib12, and cover14is fixed to housing10by fixing screws14a, thereby sealing opening11. Connection hole15is made in a bottom surface of housing10, and operation hole16is made in a ceiling surface of housing10. Positioning slits17are radially formed in an inner circumferential surface of operation hole16at intervals of 90 degrees, and circular step18is concentrically formed near an opening edge of operation hole16.

Switch main body20has an outer shape of which switch main body20can be accommodated from opening11of housing10, and switch main body20is fixed to an inside surface of housing10by three fixing screws20a.

As illustrated inFIG. 4, the front surface of switch main body20is vertically partitioned into two stages by partition rib21, hexagonal first projection22is obliquely projected in a center of the upper stage, and square second projection23is projected in the center of the lower stage. Fixed contact terminals25and26, each of which includes connection screw24and has a substantial U-shape in section, are embedded on both sides of first projection22, and fixed contact terminals27and28each of which includes connection screw24are embedded on both sides of second projection23.

Switch main body20is provided such that insulating walls29and29are pushed out onto a front side from end portions on both the sides of switch main body20.

As illustrated inFIGS. 8 and 9, operation shaft30is supported in switch main body20while being vertically slidable, and operation shaft30is biased upward by coil spring31. Therefore, an upper end of operation shaft30projects from operation hole20bmade in the ceiling surface of switch main body20. In operation shaft30, movable touch piece32inFIG. 4is vertically inverted, whereby movable contacts33provided at both ends of movable touch piece32alternately comes into contact with and separates from fixed contacts of fixed contact terminals25and26and fixed contacts of fixed contact terminals27and28.

As illustrated inFIGS. 2 and 3, plunger40has the outer shape that can vertically move along operation hole16of housing10, operating ridge42having a substantial T-shape is provided in an upper surface of guard portion41of plunger40, and guide rib43is provided in a base of a lower surface of guard portion41. Guide rib43of plunger40is selectively fitted in one of positioning slits17provided in housing10, whereby a lower end of plunger40abuts on an upper end of operation shaft30to be able to detect a rotation direction of operation lever69which is described below.

As illustrated inFIG. 2, driving mechanism50is assembled in box53that is fixed to the upper surface of housing10with seal ring51interposed therebetween by fixing screws52.

That is, as illustrated inFIG. 8, rotating shaft61is rotatably inserted in cylindrical bearing section60that is press-fixed through attachment hole55of cylindrical rib54provided in box53. The leading end portion of rotating shaft61is fitted in bearing recess56provided in the inside surface of box53, and a pair of circular cams63and64sandwiching return coil spring62is retained on a leading end side of rotating shaft61by E-ring65(for the sake of convenience, return coil spring62is not illustrated inFIGS. 8 and 9).

Particularly, as illustrated inFIG. 5A, circular cams63and64respectively include through-holes63aand64athat can be fitted in the leading end portion of rotating shaft61in which flat surface61a(FIG. 3) is provided. Ridges63band64bhaving a triangular shape in section are projected along a shaft center direction in the inner circumferential surfaces of through-holes63aand64a, respectively, and ridges63band64bcan be latched in an edge of flat surface61aof rotating shaft61. Both the ends of return coil spring62are latched in circular cams63and64to provide a biasing force in the rotation direction to rotating shaft61. This is because operation lever69, which is described later, is returned to an original position.

On the other hand, as illustrated inFIG. 2, rubber oil seal66is mounted on the rear end side of rotating shaft61projecting from cylindrical rib54, and setting position display panel67is engaged with the rear end side of rotating shaft61. Operation lever69including roller68is fixed to the rear end of rotating shaft61by adjustment screw69a.

Not only circular cams63and64are fixed by E-ring65, but also circular cams63and64may be retained by stopper65apress-fixed into the leading end portion of rotating shaft61like a second embodiment inFIG. 5B. Because other configurations of the second embodiment are similar to those of the first embodiment, the same component is designated by the same numeral, and the description is omitted.

A method for assembling the limit switch having the above constituent will be described below.

Switch main body20is inserted from opening11of housing10, and fixed by three fixing screws20a. On the other hand, guide rib43of plunger40is selectively fitted in positioning slit17provided in operation hole16of housing10. Seal ring51is fitted in circular step18provided around operation hole16, and box53is fixed to housing10by fixing screws52.

On the other hand, circular cam63, return coil spring62, and circular cam64are sequentially inserted on the leading end side of rotating shaft61, and retained by E-ring65. Cylindrical bearing section60is press-fixed into attachment hole55after rotating shaft61is inserted from attachment hole55of box53to fit the leading end portion of rotating shaft61in bearing recess56(FIG. 8) provided in the inside surface of box53. Therefore, cylindrical bearing section60abuts on the outward surface of circular cam63to retain rotating shaft61. At this point, circular cams63and64abut on operating ridge42of plunger40. Rubber oil seal66is fitted on the rear end side of rotating shaft61projecting from box53, whereby setting position display panel67is engaged while the sealing is performed. Then the operation lever69is attached to the rear end of rotating shaft61, and fixed by adjustment screw69a.

After circular seal member13is positioned in circular rib12, cover14is fixed to housing10by fixing screws14ato complete the assembly work.

In the case that lead wires are connected to switch main body20on site, after cover14is detached, connection terminals of lead wires70and71are fixed to fixed contact terminals27and28on the lower stage side, respectively, by connection screws24as illustrated inFIG. 6A. Then, as illustrated inFIG. 6B, the connection terminal of lead wire72is fixed to fixed contact terminal26by connection screw24. Finally, lead wire73is fixed to fixed contact terminal25by connection screw24to complete the connection work.

According to the first embodiment, a creeping distance is lengthened by partition rib21, and first and second projections22and23act as the insulating wall. Therefore, the limit switch having an excellent insulating characteristic is obtained.

In the case that the connection is performed by a connection structure different from that inFIG. 6, as illustrated inFIG. 7B, lead wire72is folded along first projection22and connected to fixed contact terminal25, and lead wire73may be detoured along first projection22and connected to fixed contact terminal26.

According to the first embodiment, an outer circumferential surface of first projection22has a shape (a shape, such as a substantial hexagon and a substantial parallelogram, which includes a region where at least two pairs of line segments substantially parallel to each other are coupled to each other at an angle different from a right angle when first projection22is viewed from the front surface) along wiring routes of lead wires72and73, so that advantageously the connection work can efficiently be performed.

Action of the limit switch of the first embodiment will be described below.

In the case that an external force is not applied to operation lever69as illustrated inFIGS. 8 and 9, operation lever69is vertically provided and only the pair of cams63and64abuts on operating ridge42of plunger40, but cams63and64do not push down plunger40. Therefore, operation shaft30is pushed up by a spring force of coil spring31, and movable contact33of movable touch piece32is in contact with fixed contact terminals25and26.

When operation lever69rotates clockwise by the external force, the edge on one side of flat surface61aprovided in rotating shaft61is latched in ridge63bof circular cam63. Only circular cam63rotates to push down operating ridge42of plunger40, thereby pushing down operation shaft30. As a result, movable touch piece32is pushed down and inverted, and movable contact33is switched from fixed contact terminals25and26to fixed contact terminals27and28.

When the external load is released, rotating shaft61rotates in the opposite direction by the spring force of return coil spring62, operation lever69returns to the original position, and operation shaft30and plunger40are pushed up by the spring force of coil spring31.

On the other hand, when operation lever69rotates counterclockwise by the external force, the edge on the other side of flat surface61aprovided in rotating shaft61is latched in ridge64aof circular cam64. Only circular cam64rotates to push down operating ridge42of plunger40, thereby pushing down operation shaft30. As a result, movable touch piece32is pushed down and inverted, and movable contact33is switched from fixed contact terminals25and26to fixed contact terminals27and28.

When the external load is released, rotating shaft61rotates in the opposite direction by the spring force of return coil spring62, operation lever69returns to the original position, and operation shaft30and plunger40are pushed up by the spring force of coil spring31.

In the first embodiment, guide rib43is engaged with selected positioning slit17when plunger40is assembled in housing10, for example, the clockwise external force can be detected while the counterclockwise external force is not detected.

The operation lever is not necessarily attached in the vertical direction. For example, the operation lever may be attached in a horizontal or oblique direction.

In one or more of the above embodiments, the four lead wires are connected to the limit switch by way of example. Alternatively, for example, six or eight lead wires may be connected to the limit switch.

One circular cam may be attached to the rotating shaft.

One or more embodiments of the present invention can be applied to not only the limit switch but also limit switches having other shapes.

DESCRIPTION OF SYMBOLS