Electrical resistors – Mechanically variable – Movable contact electrically adjustable over length of...
Utility Patent
2000-05-19
2001-01-02
Easthom, Karl D. (Department: 2832)
Electrical resistors
Mechanically variable
Movable contact electrically adjustable over length of...
C338SDIG001
Utility Patent
active
06169473
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a screw-driven multiturn electrical device, such as a variable resistor.
2. Description of the Related Art
A variable resistor as an example of a known screw-driven multiturn electrical device will be described with reference to
FIGS. 4
to
7
. As shown in
FIG. 4
, a wiper contact holding member
53
having the shape of a rectangular prism and holding a wiper contact
52
on its lower surface is supported on a drive shaft
54
in a resistor case
51
.
Referring to
FIGS. 5 and 6
, the wiper contact holding member
53
is combined with the drive shaft
54
by extending the drive shaft
54
in a groove
53
a
formed in a central part of the upper surface of the wiping contact holding member
53
and retaining the wiper contact holding member
53
on the drive shaft
54
by a U-shaped spring
55
having a pair of leg parts
55
a
and a crossing part
55
b
extending between the leg parts
55
a
. The spring
55
is put on the wiper contact holding member
53
with the leg parts
55
a
thereof extended obliquely across the groove
53
a
, the crossing part
55
b
thereof engaged with a projection
53
b
formed in one of the side walls of the groove
53
a
, and extreme end parts
55
c
of the leg parts
55
a
received in small grooves
53
c
formed in the other side wall of the groove
53
a.
As shown in
FIG. 7
, the leg parts
55
a
of the spring
55
are in engagement with a screw thread formed in the circumference of the drive shaft
54
, and the extreme end parts
55
c
are in elastic contact with the upper wall of the resistor case
51
.
In this known variable resistor thus composed, the drive shaft
54
is rotated to drive the wiper contact holding member
53
through the spring
55
for longitudinal movement to vary an output signal by moving the wiper contact
52
(FIG.
4
). Since the extreme end parts
55
c
of the spring
55
are in contact with the upper wall of the resistor case
51
so as to apply a moderate pressure to the upper wall, so that the wiper contact holding member
53
is restrained from rattling. When the drive shaft
54
continues to rotate after the wiper contact holding member
53
has reached either of the opposite ends of it stroke, the leg parts
55
a
of the spring
55
are disengaged from the screw thread of the drive shaft
54
, so that any excessive force is exerted on the wiper contact holding member
53
.
In this known variable resistor, however, the disengagement of the leg parts
55
a
of the spring
55
from the screw thread of the drive shaft
54
is repeated when the drive shaft
54
continues to rotate after the wiper contact holding member
53
has reached either of the opposite ends of its stroke. Consequently, the leg parts
55
a
of the spring
55
are rubbed by the screw thread of the drive shaft
54
and noise is generated.
Since the leg parts
55
a
of the spring
55
are disengaged from the screw thread of the drive shaft
54
when the drive shaft
54
continues to rotate after the wiper contact holding member
53
has reached either of the opposite ends of it stroke, the wiper contact holding member
53
does not start moving immediately even if the rotation of the drive shaft
54
is reversed, until the leg parts
55
a
of the spring
55
are engaged with the screw thread of the drive shaft
54
. The variable resistor having such a lost motion cannot be used for some purposes.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a screw-driven multiturn electrical device not generating noise and capable of being applied to all kinds of purposes.
According to one aspect of the present invention, a screw-driven multiturn electrical device comprises: an operating shaft provided with a screw thread in its circumference and having at least one end part provided with a first projection; an internally threaded carrying member in engagement with the screw thread of the operating shaft and provided with a second projection that is brought into engagement with the first projection serving as a stopper at the end of the operating shaft; and a moving member in frictional engagement with the internally threaded carrying member; wherein the moving member moves together with the internally threaded carrying member toward the end of the operating shaft when the operating shaft is rotated in one direction to change the level of electric signal, the internally threaded carrying member is turned together with the operating shaft against a frictional resistance exerted thereon by the moving member after the second projection of the internally threaded carrying member has been brought into engagement with the first projection of the operating shaft, and the second projection is separated from the first projection and the moving member moves axially together with the internally threaded carrying member toward an axially middle part when the rotation of the operating shaft rotating together with the internally threaded carrying member is reversed.
This screw-driven multiturn electrical device does not generate any noise because the internally threaded carrying member turns together with the operating shaft against the frictional resistance exerted thereon by the moving member. Since the first and the second projection are separated from each other and the moving member moves axially toward an axially middle part when the rotation of the operating shaft is reversed, the screw-driven multiturn electrical device can be applied to all kinds of purposes.
In the screw-driven multiturn electrical device according to the present invention, it is preferable that the moving member has an external shape resembling that of a structure formed by combining semicylindrical parts and a flat part, the flat part is provided with an opening through which the internally threaded carrying member is received, the semicylindrical parts are arranged so as to define a groove for receiving a part of the internally threaded carrying member therein for the frictional engagement of the moving member and the internally threaded carrying member. The internally threaded carrying member and the moving member of this screw-driven multiturn electrical device can be easily assembled.
REFERENCES:
patent: 2862089 (1958-11-01), Mairs
patent: 3634805 (1972-01-01), Jestrzemski et al.
patent: 3670286 (1972-06-01), Bang et al.
patent: 3694788 (1972-09-01), Perrisini
patent: 3938070 (1976-02-01), Koerner et al.
patent: 6078249 (2000-06-01), Slavik et al.
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Easthom Karl D.
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