Position sensor with directing mechanism

Details Position sensor with directing mechanism Position sensor with directing mechanism

2001-05-17

2003-02-11

Enad, Elvin (Department: 2832)

Electricity: circuit makers and breakers

Special application

Stationary feeler detects transient object

C200S302200

Reexamination Certificate

active

06518522

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a position sensor for sensing the position of a moving part capable of actuating a plunger belonging to the sensor. More specifically the invention discloses a mechanism for orienting the plunger of the sensor.
DESCRIPTION OF THE RELATED ART
A position sensor is a device designed to be actuated by a moving part, either because of the shape of its plunger or because of the force required to actuate it.
The position of the moving part is sensed by the mechanical action which the part exerts on the plunger when in contact with it.
Position sensors are usually fitted with miniature switches combining a reliable system of rapid switching with a sealed enclosure that confines the contacts in a neutral gas atmosphere favorable to the switching of low-level circuits up to high currents. The displacement of the plunger by the moving part actuates the miniature switch and closes or opens an electrical contact which signals the presence of the moving part.
The shape of that part of the plunger which comes into contact with the moving part is adapted both to the shape of the moving part whose position is to be detected and to the type of movement of the part. The reason for this is that, depending on the configuration of the mechanical system in which the sensor is inserted, the angle of attack defined between the direction of the movement of the moving part and the axis of the plunger, when contact occurs between the moving part and the plunger, can differ.
For example, if the displacement of the moving part is in the direction of the axis of the plunger, the free end of the plunger can simply be a hemispherical surface giving point contact with the moving part. With this same type of displacement, the free end of the plunger may be fitted with a ball able to pivot in the plunger in order to provide frictionless contact with the mechanical part, if the latter exhibits lateral movement with respect to the plunger axis.
In cases where the moving part exhibits a linear movement more or less at right angles to the plunger axis, the plunger comprises at its free end a roller oriented in the direction of movement of the part, the roller being integral with the plunger and being able to rotate about an axis of rotation perpendicular to the axis of the plunger.
FIG. 1
a
shows a partial section through a position sensor
10
according to the prior art, comprising a roller
12
, a guide
14
that can be rotationally oriented about a first axis XX′ of rotation, in a body
16
and a plunger
18
sliding without rotation in the guide
14
along this first axis XX′.
At the free end of the plunger is the roller
12
which is of circular cylindrical shape and can turn on a spindle or shaft
20
about a second axis YY′ of rotation, this second axis YY′ being colinear with the axis of revolution of the roller, and perpendicular to the first axis XX′.
When a moving part P travelling in a direction Dz approximately perpendicular to the first axis XX′ and to the second axis YY′ contacts the roller
12
on a point of its cylindrical surface situated above the second axis YY′, a first force F
1
is exerted by the moving part P on the periphery of the roller. This first force F
1
, transmitted to the plunger
18
through the shaft
20
, produces a component force F
2
in the direction of the first axis XX′. This component force F
2
causes the plunger
18
to slide down the guide
14
, and the roller
12
down two guide grooves
22
situated in the guide
14
on either side of the first axis XX′.
The sliding of the plunger down the guide takes place without rotation, the second axis YY′ of rotation of the roller
12
being maintained in the same direction throughout the sliding of the roller in the guide grooves
22
.
As it slides down the guide
14
, displaced by the component force F
2
towards the interior of the body, the plunger
18
actuates, via a rod
24
, an electric microswitch
26
. A return spring
28
is compressed during the displacement of the plunger towards the interior of the body. When the moving part P moves away from the roller, the plunger
18
is returned to its initial position by the return spring
28
.
The body
16
of the position sensor is mounted on a frame (not shown in
FIG. 1
a
) and is thus immobilized in its position with respect to the direction of displacement of the moving part. As a consequence the roller
12
must be able to be oriented and maintained in its angular position about the first axis XX′ so that the second axis YY′, about which the roller revolves, is essentially perpendicular to the direction Dz of the movement of the moving part whose position is to be detected. Having the roller oriented in the direction of movement of the moving part ensures that the roller turns properly on its spindle and avoids lateral loads during contact with the moving part.
To this end, the lower part of the guide
14
comprises position grooves
30
distributed around its periphery at an angular pitch a about the first axis XX′. At the upper end of the body
16
, the sensor possesses a locator
32
which is fixed so that it cannot rotate in the body of the sensor and which is in the form of a washer with a tooth
34
designed to fit into one of the position grooves
30
.
The body has a screwthread
35
on its cylindrical outer surface on which a nut
36
is screwed to clamp the guide
14
and the locator
34
firmly to the body
16
.
FIG. 1
b
shows a perspective view of the guide
14
showing the position grooves
30
distributed around the periphery of the guide at-an angular pitch &agr; of 45 degrees.
An angular position &bgr; of the guide grooves
22
, and consequently the angular position of the roller
12
sliding in these grooves with respect to a reference axis ZZ′ of the sensor passing through the first axis XX′ and through the middle of the tooth
34
of the locator
32
, will consequently be determined by the selection of one of the position grooves
30
, which contains the tooth
34
.
The drawing of
FIG. 1
c
shows a simplified top-down view of the sensor taken on AA′, where the angular position &bgr; of the guide grooves
22
is approximately 90 degrees with respect to the reference axis ZZ′. In this configuration the second axis YY′ of the roller
12
shown in dashes in
FIG. 1
c
will have turned through the angle &bgr; of 90 degrees with respect to its position in
FIG. 1
a.
FIG. 2
a
shows a view of the principle of a position sensor
40
according to the prior art showing another mechanism for the angular positioning of a plunger
42
with respect to a fixed body
44
of the sensor.
The position sensor
40
comprises, as in the case of the sensor of
FIG. 1
a,
a guide
46
that can be oriented rotationally about the first axis XX′ in the body
44
, with the plunger
42
sliding without rotation in the guide
46
along this first axis XX′.
In this embodiment the guide
46
has first holes
48
distributed radially with an angular pitch &agr; about the first axis XX′. The axes of the holes all lie in the same plane perpendicular to the first axis XX′, and each hole
48
can be lined up with the open end of a second hole
50
in the periphery of the body
44
.
A locator in the form of a flexible circular collar
52
encircles the body
44
of the sensor around its periphery.
FIG. 2
b
shows the collar
52
with a short rod
54
in its center which can be inserted into the second hole
50
of the body and into one of the first holes
48
-
1
of the guide lined up with the first. Selecting one of the second holes
48
-
2
and keeping it lined up with the first hole by means of the rod
54
ensures an angularly position &bgr; of the guide with respect to the sensor body.
The different mechanisms of angular positioning for sensors in the prior art have drawbacks as follows.
In operation, the sensor suffers impacts when contact occurs between the moving part and the roller. These repe

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