Electricity: electrothermally or thermally actuated switches – Electrothermally actuated switches – With bimetallic elements
Reexamination Certificate
2000-03-01
2001-08-14
Scott, J. R. (Department: 2832)
Electricity: electrothermally or thermally actuated switches
Electrothermally actuated switches
With bimetallic elements
C337S085000, C337S094000
Reexamination Certificate
active
06275134
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a durable safety switch, which automatically trips off upon an overload.
2. Description of the Related Art
FIG. 1
shows a regular switch, which comprises an electrically insulative housing
100
, three metal contact plates
110
a-c
fastened to the bottom sidewall
101
of the housing
100
, a lever
120
disposed at the topside of the housing
100
, a neon light
130
mounted in the lever
120
, the neon light
130
having a first end disposed corresponding to one lateral metal contact plate
110
c
and a second end, a metal frame
150
coupled to the middle metal contact plate
110
b
, the metal frame
150
having a contact
151
aimed at a contact
111
at one lateral metal contact plate
110
a
, and a metal spring
140
connected between the metal frame
150
and the second end of the neon light
130
. When one end of the lever
120
is depressed, the first end of the neon light
130
is forced into contact with the corresponding lateral metal contact plate
110
a
, and at the same time the spring
140
is compressed to force the metal frame
150
to tile in direction reversed to the lever
120
, thereby causing the contact
151
of the metal frame
150
to be forced into contact with the contact
111
at the other lateral metal contact plate
110
a
, and therefore the circuit is closed. When the other end of the lever
120
is depressed, the neon light
130
is disconnected from the corresponding lateral metal contact plate
110
c
, and the metal frame
150
is tilted in the reversed direction and disconnected from the other lateral metal contact plate
110
b
to open the circuit. This structure of switch is not safe in use. In case of an overload when the circuit is closed, the metal frame
150
does not automatically trip off to open the circuit, and the load may be burnt out.
FIG. 2
shows another conventional safety switch. This structure of safety switch comprises an electrically insulative housing
200
, three metal contact plates
220
a-c
fastened to the bottom side of the housing
200
, a lever
210
pivoted to the housing
200
at the top side, a metal frame
230
fixedly fastened to the middle metal contact plate
220
b
, a bimetal element
240
having a first end fastened to the top side of the metal frame
230
and a second end, a C-shaped spring
241
having one end pivoted to the second end of the bimetal element
240
and an opposite end connected to the bottom side of the metal frame
220
, a first contact
242
disposed at the bimetal element
240
, and a second contact
221
disposed at one lateral metal contact plate
220
c
adjacent to the first contact
242
. When an overload occurs, the bimetal element
240
is heated and disengages from contact with the contact
221
of the metal contact plate
220
c
trip to cut off the power supply. This structure of switch is safe in use. However, this structure of safety switch is not durable because the bimetal element
240
breaks quickly with repeated use.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, the safety switch comprises a housing holding a pivoted lever at the top and three metal contact plates at the bottom, a movable member pivoted to the intermediate metal contact plate, a bimetal element having a fixed end connected to one end of the movable member and a free end suspended above one lateral metal contact plate, an actuating member coupled between the lever and the movable member and driven by the lever to tilt the movable member between the first position where the free end of the bimetal element is forced into contact with the corresponding lateral metal contact plate, causing the circuit to be closed, and a second position where the free end of the bimetal element is disconnected from the corresponding lateral metal contact plate, causing the circuit to be opened, the bimetal element being heated to curve and to trip off upon an overload after the movable member has been moved to the first position. Because the bimetal element is horizontally extended and moved with the movable member, it is never stretched when the lever is operated. According to another aspect of the present invention, an adjustment member is mounted on the closed bottom side of the housing for adjusting the turning angle of the movable member on the second metal contact plate to control the trip off time of the bimetal element.
REFERENCES:
patent: 4167720 (1979-09-01), Krasser
patent: 4528538 (1985-07-01), Andersen
patent: 5223813 (1993-06-01), Cambreleng et al.
patent: 5491460 (1996-02-01), Krasser et al.
patent: 5742219 (1998-04-01), Moalem et al.
patent: 6072381 (2000-06-01), Yu
patent: 6094126 (2000-07-01), Sorenson
Bacon & Thomas PLLC
Scott J. R.
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