Electricity: circuit makers and breakers – Multiple circuit control – Pivoted contact
Reexamination Certificate
1997-06-02
2001-07-17
Luebke, Renee (Department: 2833)
Electricity: circuit makers and breakers
Multiple circuit control
Pivoted contact
C200S00100B, C200S522000, C200S240000
Reexamination Certificate
active
06262380
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a switching device and, more specifically, to a switching device suitably used for normal/reverse rotation switching, rotational speed switching, and the like typically in power tools such as an electric drill and an electric screwdriver.
2. Description of the Related Art
FIG. 29
shows a circuit configuration of the main part of a conventional trigger switch (switching device) which is used in a power tool such as an electric drill.
FIG. 30
is its vertical sectional view, and
FIG. 31
is its partially cutaway plan view.
The trigger switch is provided with the following components. A pair of changeover switches
73
and
74
operate in link motion to switch the connections of both terminals of a DC motor
51
for drill blade driving in response to a manipulation on a switching lever
50
for normal/reverse rotation switching of the DC motor
51
. A brake switch
54
brakes the DC motor
51
by short-circuiting both terminals thereof when a manipulation lever (trigger)
53
, which is pulled by fingers for drill blade rotary driving, is at the free position, i.e., non-manipulation position. A first switch
56
connects a DC power supply to the DC motor
51
via a FET
55
for rotational speed control. A second switch
57
short-circuits the DC motor
51
with the DC power supply to rotate the DC motor
51
at the maximum speed when the manipulation lever
53
is pulled to the full stroke. A diode
58
is also provided.
As shown in
FIG. 30
, the brake switch
54
is composed of a braking movable contact
61
mounted on a manipulation shaft
60
which is urged in the direction of arrow C by means of a return spring
59
, a coil spring
62
for urging the movable contact
61
in the direction of arrow C, and top and bottom braking fixed contacts
63
and
64
which are mounted on a case. When the manipulation lever
53
is at the free position where it is not pulled by fingers in the direction of arrow D in
FIG. 30
, the braking movable contact
61
is in pressure contact with the braking fixed contacts
63
and
64
, whereby the brake switch is on to brake the DC motor
51
.
The first switch
56
is composed of a fixed contact
65
which is mounted on a top portion of the case and a movable piece
68
which is urged by a coil spring
66
so that a movable contact
67
is brought into pressure contact with the fixed contact
65
. At the free position, the free end of the movable piece
68
is placed on a protrusion
60
b
at a top portion of a plunger
60
a
of the manipulation shaft
60
, whereby the contacts
65
and
67
are separated from each other and hence the first switch
56
is in an off-state.
The second switch
57
is composed of a fixed switch
69
which is mounted on a bottom portion of the case and a movable piece
72
which is urged by a coil spring
70
so that a movable contact
71
is brought into pressure contact with the fixed contact
69
. At the free position, the free end.of the movable piece
72
is placed on a protrusion
60
c
at a bottom portion of the plunger
60
a
of the manipulation shaft
60
, whereby the contacts
69
and
71
are separated from each other and hence the second switch
57
is in an off-state.
The first and second changeover switches
75
and
76
, which are linked with each other to operate to switch the connections of both terminals of the DC motor
51
in response to a switching manipulation on the switching lever
50
, are composed of fixed contacts
75
and
76
connected to the respective terminals of the DC motor
51
, changeover contacts
77
and
78
to effect a changeover operation in response to a manipulation on the switching lever
50
, fixed contacts
79
and
80
connected to the positive side of the DC power supply, and fixed contacts
81
and
82
to be connected to the negative side of the DC power supply via the first switch
56
and the FET
55
or the second switch
57
.
The switching lever
50
(manipulating section) is pivotable about a pivot
83
in accordance with a switching manipulation. As shown in
FIGS. 30 and 31
, a protrusion
84
a
of a changeover cam
84
(changeover section) which is provided with the changeover contacts
77
and
78
of the first and second changeover switches
73
and
74
is engaged with an end portion of the switching lever
50
. In accordance with a switching manipulation on the switching lever
50
which acts on the changeover cam
84
via the protrusion
84
a
, the changeover cam
84
pivots about a pivot
85
which is different from the pivot
83
of the switching lever
50
. As shown in
FIG. 31
, the fixed contacts
75
,
76
, and
79
-
82
of the first and second changeover switches
73
and
74
are disposed around the changeover cam
84
. In
FIG. 31
, reference numerals
90
and
91
are a radiation plate and a screw, respectively.
FIGS. 32A-32C
show connection states between the changeover contacts
77
and
78
of the changeover cam
84
and the fixed contacts
75
,
76
, and
79
-
82
;
FIG. 32A
shows a neutral state,
FIG. 32B
shows a normal rotation state, and
FIG. 32C
shows a reverse rotation state.
When the switching lever
50
in in the neutral state, the changeover contacts
75
and
76
of the changeover cam
84
are respectively connected to only the fixed contacts
75
and
76
which are connected to the respective terminals of the DC motor
51
. When switching in made from the neutral state to the normal rotation state by a switching manipulation on the switching lever
50
, the changeover cam
84
rotates to connect the fixed contacts
75
and
79
(
80
) via the changeover contact
77
while connecting the fixed contacts
76
and
81
(
82
) via the changeover contact
78
, to establish the intended normal rotation state. On the other hand, when the normal rotation state is selected by manipulating the switching lever
50
in the opposite direction, the changeover cam
84
rotates to connect the fixed contacts
75
and
81
(
82
) via the changeover contact
77
while connecting the fixed contacts
76
and
79
(
80
) via the changeover contact
78
, to establish the intended reverse rotation state.
Next, the operation of the above conventional trigger switch will be described.
It is now assumed that, for instance, the changeover switches
73
and
74
are in the state of
FIG. 32B
, that is, the normal rotation state is selected by manipulating the switching lever
50
.
First, at the free position where the manipulation lever
53
is not pulled by fingers at all, the brake switch
54
is on while the first and second switches
56
and
57
are off, as described above.
When the manipulation lever
53
is pulled from the free position, after a play stroke the braking movable contact
61
of the manipulation shaft
60
is separated from the braking fixed contacts
63
and
64
to turn off the brake switch
54
. Then, the free end of the movable piece
68
of the first switch
56
goes over the protrusion
60
b
at the top portion of the plunger
60
a
, so that the movable contact
67
rotates to contact with the fixed contact
65
(see FIG.
33
), to thereby turn on the first switch
56
. Supplied with power in this manner, the DC motor
51
starts to rotate in the normal direction. Further, in accordance with the pulling stroke of the manipulation lever
53
, a brush
88
which is provided in the plunger
60
a
of the manipulation shaft
60
slides on a resistor of a circuit board (not shown), whereby a current corresponding to a slide position is supplied to the DC motor
51
via the FET
55
for rotational speed control. Thus, the DC motor
51
rotates at a rotational speed corresponding to the pulling stroke of the manipulation lever
53
.
When the pulling stroke of the manipulation lever
53
reaches a predetermined value, the free end of the movable piece
72
goes over the protrusion
60
c
at the bottom portion of the plunger
60
a
of the manipulation shaft
60
, so that the movable contact
671
rotates to contact with the fixed contact
69
, to ther
Sasaki Shunkichi
Yonezawa Tatsushi
Luebke Renee
Morrison & Foerster / LLP
Omron Corporation
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