Geometrical instruments – Miscellaneous – Light direction
Reexamination Certificate
2001-04-17
2004-02-10
Gutierrez, Diego (Department: 2859)
Geometrical instruments
Miscellaneous
Light direction
C033S0010PT
Reexamination Certificate
active
06688006
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a sensor assembly for detecting the angle of rotation of elements relative to each other and, more particularly, to the rotational angle sensor assembly for use in construction machinery and industrial machinery for detecting the angle of rotation of a rotating element such as, for example, a rotary shaft or an oscillating shaft while the latter is operated under a loaded condition.
2. Description of the Prior Art
As an instrument for measuring the angle of rotation of a rotary shaft or an oscillating shaft, a rotational angle detecting potentiometer has long been used. The rotational angle detecting potentiometer includes an electroconductive brush movable together with, for example, a rotary shaft and an electric resistor held in sliding contact with the brush. The potentiometers provides a voltage signal represented by the resistance of the resistor which varies depending on the position of the electroconductive brush, so that the angle of rotation of the rotary shaft can be determined in reference to the voltage signal.
The standard rotational angle detecting potentiometer hitherto used makes use of an oil retaining metal or a relatively small rolling bearing in order to permit the rotary shaft to be rotatably supported relative to a housing and is incapable of allowing the rotary shaft to be loaded with a relatively high load. When a relatively high load is imposed on the rotary shaft in one or both of axial and radial directions thereof, a relatively large error tends to occur in the detected angle of rotation.
In order to alleviate the foregoing problem, the rotational angle sensor assembly of a structure shown in
FIG. 4
has been suggested by the applicant. Referring to this figure, the rotational angle sensor assembly shown therein includes a rotary shaft
52
having a large diametric portion
52
a
formed therein so as to protrude radially outwardly therefrom and supported by a housing
51
through bearings
53
. The housing
51
is in the form of a cap sufficient to accommodate therein both the large diametric portion
52
a
of the rotary shaft
52
and the bearing
53
and having an opening closed by a lid
54
. The lid
54
is secured to the housing
51
by means of a plurality of set bolts
58
. First and second rotational angle detecting members
56
and
57
altogether forming a rotational angle detecting means
55
are mounted on an inner surface of the lid
54
and an end face of the rotary shaft
52
, respectively. One of the detecting members
56
and
57
is made up of an electric resistor and the other is made up of an electroconductive brush. The bearings
53
are positioned within the housing
51
coaxially one above the other with an annular space left therebetween. Within the annular space between the bearings
53
, a flange
52
b
radially outwardly extending from the rotary shaft
52
is interposed between respective inner races of those bearings
53
whereas an annular spacer
59
is interposed between respective outer races of those bearings
53
.
According to the structure shown in
FIG. 4
, since the bearings
53
are preloaded at a predetermined position and, also, since the rotary shaft
52
is formed with the large diametric portion
52
a
to enable the bearings
53
of a relatively large size to be employed, the rigidity with which the rotary shaft
52
is supported can increase advantageously and, even in a condition in which a load acts on the rotary shaft
52
, the angle of rotation of the rotary shaft
52
relative to the housing
51
can advantageously be detected accurately and with no error occurring.
However, the rotational angle sensor assembly of the structure shown in and described with reference to
FIG. 4
has the following disadvantage. Specifically, since the housing
51
and the lid
54
carrying the first rotational angle detecting member
56
including a potentiometer substrate and others are members separate from each other, any possible error in mounting the lid
54
to the housing
51
such as resulting from, for example, a play occurring between one or more set bolts
58
and associated bolt holes may brings about a detrimental displacement of the reference or base position from which an output representative of the angle of rotation of the rotary shaft
52
relative to the housing
51
is based. In other words, where the rotational angle detecting means
55
is assembled in the form of a potentiometer made up of an electric resistor and an electroconductive brush, an electrically neutral position (normally, a zero reading position of the potentiometer) relative to the housing
51
may detrimentally displace as a result of an error in mounting of the lid
54
relative to the housing
51
. In addition, the employment of the lid
54
brings about the necessity to use, other than the lid
54
, the set bolts
58
and an O-ring seal
60
to be interposed between the lid
54
and the housing
51
, resulting in increase of the number of component parts.
Also, in order for the bearings
53
to be set in position under a pre-loaded condition, the annular spacer
59
and/or the flange
52
b
between the two bearings
53
must have a thickness carefully designed to be consistent with the size of the bearings and do thus require a precise machining accuracy, resulting in increase of the cost of manufacture.
SUMMARY OF THE INVENTION
In view of the foregoing, the present invention is intended to provide an improved rotational angle sensor assembly effective to minimize variation of the reference or base position from which the output representative of the angle of rotation of, for example, the rotary shaft relative to the housing, to reduce the number of component parts employed and also to effectively and sufficiently support the load acting on the rotary shaft.
Another important object of the present invention is to provide an improved rotational angle sensor assembly of the type referred to above, which does not substantially require a precise machining accuracy in mounting the bearings under a pre-loaded condition and which can be easily and inexpensively assembled using a simplified machining.
In order to accomplish these objects of the present invention, there is provided a rotational angle sensor assembly which includes a generally cup-shaped housing having an opening leading into a hollow defined therein, a rotary shaft having first and second ends opposite to each other, and a rotational angle detecting means including first and second rotational angle detectors and operable to detect the angle of rotation between the first and second rotational angle detectors. The first rotational angle detector is disposed at a bottom of the hollow of the housing. The second rotational angle detector being mounted on the first end of the rotary shaft within the hollow of the housing. A first portion of the rotary shaft adjacent the second end thereof extends outwardly from the opening of the housing. A bearing means is accommodated within the hollow of the housing under a pre-loaded condition for rotatably supporting the rotary shaft.
According to the present invention, the angle of rotation of the rotary shaft relative to the housing is detected in terms of the angle of rotation between the first and second rotary angle detectors provided in and on the housing and the rotary shaft, respectively. Since the housing is of a generally cup-shaped structure with the first rotational angle detector disposed directly at the bottom of the hollow of the housing, unlike the conventional design in which a rotational angle detector is mounted on a lid which is in turn secured to a housing, the present invention is advantageous in that no variation in output indicative of the angle of rotation due to an error in mounting will occur which would otherwise result from a mounting error. Also, the housing is of a solid one-piece structure, not only is the need to use any lid eliminated, but the need to use any bolts otherwise necessary to secure the lid to th
Guadalupe Yaritza
Gutierrez Diego
NTN Corporation
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