Mechanical movement

A mechanical movement is provided for converting between linear and rotational movement and includes a frame adapted to move only along a linear path of travel. A first rotatable member is adapted to bear against the frame in such a manner that the first rotatable member is free to rotate with respect to the frame. A second rotatable member is adapted to bear against the first rotatable member in such a manner that the second rotatable member is free to rotate with respect to the first rotatable member in an eccentric fashion. A third rotatable member is affixed to the second rotatable member and is adapted to rotate therewith about a fixed axis. Means are provided for minimizing the sideward thrust on the first and second rotatable members so that linear movement of the frame will be converted to rotational movement of the third rotatable member and so that rotational movement of the third rotatable member will be converted to linear movement of the frame. The third rotatable member may also be connected to a valve stem for opening and closing a valve, so that linear movement of the frame will result in rotational movement of the valve stem.

BACKGROUND OF THE INVENTION 
The present invention relates generally to mechanical movements and more 
particularly to a mechanical movement for converting between linear and 
rotational movement. 
In a wide variety of prior applications it has frequently been desirable to 
mechanically convert between linear and rotational movement. Most prior 
devices that have accomplished such a conversion have been space 
consuming, expensive, and have had a rather limited load capability. 
However, as is illustrated in U.S. Pat. No. 1,867,981 to Mudd, a more 
simple mechanical movement is known for changing reciprocating linear 
movement to rotational movement. The movement shown in Mudd includes a 
ring secured to a piston rod. Mounted inside the ring by means of roller 
bearings are eccentric plates with an output shaft affixed to the 
innermost eccentric plate to yield rotational movement in response to the 
reciprocating movement of the piston. A similar mechanical movement is 
illustrated in U.S. Pat. No. 2,782,646 to Christian. Although movements of 
the type discussed above are capable of functioning when relatively 
lightly loaded, it has now been discovered that certain stresses are 
produced during the operation of such a movement which have prevented its 
use under heavier load conditions. 
SUMMARY OF THE INVENTION 
Accordingly, a mechanical movement is provided for converting between 
linear and rotational movement and includes a frame adapted to move only 
along a linear path of travel. A first rotatable member is adapted to bear 
against the frame in such a manner that the first rotatable member is free 
to rotate with respect to the frame. A second rotatable member is adapted 
to bear against the first rotatable member in such a manner that the 
second rotatable member is free to rotate with respect to the first 
rotatable member in an eccentric fashion. A third rotatable member is 
affixed to the second rotatable member and is adapted to rotate therewith 
about a fixed axis. Means are provided for minimizing the sideward thrust 
on the first and second rotatable members so that linear movement of the 
frame will be converted to rotational movement of the third rotatable 
member and so that rotational movement of the third rotatable member will 
be converted to linear movement of the frame. The third rotatable member 
may also be connected to a valve stem for opening and closing a valve, so 
that linear movement of the frame will result in rotational movement of 
the valve stem. 
Objects of the Invention 
An object of the present invention is the provision of a mechanical 
movement for converting between linear and rotational movement which can 
operate under a substantial load. 
Another object of the present invention is the provision of a mechanical 
movement for converting between linear and rotational movement which 
occupies a relatively small amount of space. 
A further object of the present invention is the provision of a mechanical 
movement for converting between linear and rotational movement which 
comprises a small number of easily fabricated elements permitting ease and 
economy of manufacture. 
Still another object of the present invention is the provision of a 
mechanical movement for converting between linear and rotational movement 
which is suitable for use as a valve actuator. 
Other objects, advantages, and novel features of the present invention will 
become apparent from the following detailed description of the invention 
when considered in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a valve actuator 10 including the mechanical movement of the 
present invention. The actuator includes a frame 12 which moves only along 
a linear path of travel. The frame 12 receives a linear input from a unit 
14 connected thereto. The linear input unit 14 is shown in block form only 
and may be any prime mover having sufficient linear force to propel the 
actuator in a given application. Preferably, the unit 14 is a short stroke 
diaphragm operated device. The frame 12 has an opening or bore 16 therein 
which defines an inner surface for the frame 12. The first rotatable 
member 18 is positioned within the opening 16 of frame 12 and is adapted 
to bear against the inner surface of frame 12 in such a manner that the 
first rotatable member 18 is free to rotate with respect to the frame 12. 
The rotatable member 18 is preferably a cylindrical disc and has an 
opening or bore 20 eccentrically therein which defines an inner surface 
for the rotatable member 18. A second rotatable member 22 is positioned 
within the opening 20 in the first rotatable member 18 and is adapted to 
bear against the inner surface of the first rotatable member 18 in such a 
manner that the second rotatable member 22 is free to rotate with respect 
to the first rotatable member 18 in an eccentric fashion. A third 
rotatable member 24 is affixed eccentrically to the second rotatable 
member 22 and is adapted to rotate therewith about a fixed axis 26. The 
second rotatable member 22 is preferably a cylindrical disc, and the third 
rotatable member 24 is preferably a shaft. The shaft 24 may be integral 
with the disc 22 or may be affixed to the disc 22 by any suitable means, 
such as, by pinning the shaft 24 to the disc 22. The shaft 24 is either 
connected to a valve stem or, as shown in FIGS. 1 and 2, is a valve stem. 
The valve stem 24 may in turn be connected, for example, to a butterfly 
valve 28 located within a conduit 30. The valve stem 24 serves to open and 
close the butterfly valve 28 in response to rotational movement of the 
stem 24. As will be seen later, linear movement of the frame 12 results in 
rotational movement of the valve stem 24 and thus serves to open and close 
the valve 28. Although a bushing interface between moving surfaces is 
illustrated in FIGS. 1 and 2, it is to be understood that if necessary, 
either needle, roller, or ball bearings may be inserted along the inner 
surfaces 16 and 20 of frame 12 and rotatable member 18, respectively. 
The valve actuator 10 further includes means connected to the rotatable 
members 18 and 22 for forming a positive coupling between the members 18 
and 22, whereby linear movement of the frame will be converted to 
rotational movement of the stem 24 and whereby rotational movement of the 
stem 24 will be converted to linear movement of the frame 12. The means 
for forming a positive coupling includes means for forcing one of the 
members 18 and 22 to rotate in a first direction in response to rotational 
movement by the other of the members 18 and 22 in a direction opposite to 
the first direction. 
The means for forming a positive coupling preferably comprises a mechanical 
coupling which includes a first drive means affixed to the rotatable 
member 18 and adapted to rotate therewith. The first drive means is 
preferably an internal sector or ring gear 32 which is affixed to the 
rotatable member 18 by means of a plurality of arms 34. The mechanical 
movement of the present invention further includes a second drive means 
which is affixed to the rotatable member 22 and adapted to rotate 
therewith. The second drive means preferably includes an arm 36 which is 
affixed to the rotatable member 22 and a pair of spur gears 38 and 40 
journalled on the end of the arm 36 so as to be free to rotate with 
respect to the arm 36, but not with respect to each other. For example, 
the spur gears 38 and 40 could be pinned to a common shaft, to thereby 
force the spur gears to rotate in unison. 
The mechanical movement of the present invention further includes a third 
drive means which is fixed to ground, so as to be incapable of either 
rotational or linear movement. The third drive means is preferably a 
grounded gear 42. The grounded gear 42 is preferably a circular internal 
or ring gear which is centered about the axis of rotation 26 of stem 24. 
The gear 42 may be grounded in any suitable manner, for example, by 
affixing the gear 42 to the conduit 30. This is preferably accomplished by 
mounting the gear 42 on the valve actuator housing. The grounded gear 42 
is adapted to engage the spur gear 38, and the internal sector gear 32 is 
adapted to engage the spur gear 40. As will be explained in more detail 
later, the center of the rotatable member 22 rotates about the fixed axis 
26, and the sector gear 32, although fixed to rotatable member 18, is 
concentric with rotatable member 22. The frame 12, the rotatable members 
18 and 22 and the shaft 24 may be manufactured from any material of 
suitable strength, such as, cast iron. The gears may also be manufactured 
from any material of suitable strength, such as, a stamped metal. 
The operation of the mechanical movement of the present invention will now 
be described in detail in connection with FIGS. 3A through 3E. In FIGS. 3A 
through 3E, the outer edge 50 of the shaft 24 is coincident with the locus 
of the central axis of rotatable member 22 as the shaft 24 rotates through 
360 degrees. In addition, it should be noted that the eccentricity between 
the shaft 24, the rotatable member 22, and the rotatable member 18 is such 
that in the "dead center" position shown in FIG. 3A the central axis 26 of 
shaft 24 is spaced a distance e from the central axis of the rotatable 
member 22. Likewise, the central axis of the rotatable member 22 is spaced 
a distance e from the central axis of the rotatable member 18. Thus, the 
central axis 26 of shaft 24 is spaced a distance 2e from the central axis 
of rotatable member 18. If the movement is moved off "dead center" by 
clockwise or rotational movement of the shaft 24 or if the movement is 
initially off "dead center" and if a linear force input is applied to the 
frame 12, the shaft 24 and the rotatable member 22 will begin to rotate in 
a clockwise direction through an angle .beta.. The rotatable member 18 
will rotate in the counterclockwise direction about its moveable central 
axis the same angle .beta.. Thus, in FIG. 3B the rotatable members 18 and 
22 have rotated through an angle of 45 degrees and the frame 12 has moved 
downward a distance 0.586 e. In FIG. 3C the members 18 and 22 have rotated 
through an angle of 90 degrees, and the frame 12 has moved downward a 
distance 2e. In FIG. 3D the members 18 and 22 have rotated through 135 
degrees, and the frame 12 has moved downward a distance 3.414 e. In FIG. 
3E the members 18 and 22 have rotated through 180 degrees, and the frame 
12 has moved downward a distance 4e. If the shaft 24 were used as a 
rotatable input and rotated continuously, it is apparent that the frame 12 
will follow a reciprocating linear path having a total stroke equal to 4e. 
In order to emphasize the importance of minimizing the sideward thrust on 
rotational members 18 and 22 by providing a positive coupling 
therebetween, FIG. 4 shows a graph of side thrust for a unit linear input 
thrust versus the angular position, as measured by the angle .beta., of a 
mechanical movement not including the positive coupling of the present 
invention. This graph is a theoretical representation in that it assumes 
zero friction between all moving parts. It can easily be seen from FIG. 4, 
that as the rotatable members 18 and 22 approach 90 degrees, the position 
shown in FIG. 3C, infinite sideward thrust builds up on the members 18 and 
22. In practice, prior art movements of the present type, without the 
positive coupling of the present invention, tended to bind near the 90 
degree position. Thus, it can be seen that under light load conditions 
prior art movements of the present type would tend to build up stress 
approaching the 90 degree position and then experience a rapid decrease in 
stress just past the 90 degree position. This would result in a snap 
action past the 90 degree position, putting undue stress on both the 
output shaft and the linear input device. Under heavy load conditions it 
is apparent that prior art movements would tend to bind near the 90 degree 
position and even cause shearing of input and output members. 
FIG. 5 illustrates a graph of the output torque at shaft 24 of the present 
invention as the angle .beta. varies from zero to 180 degrees. Once again, 
this is a theoretical graph in that it assumes no friction between moving 
parts. It is evident that at 0 degrees and at 180 degrees, output torque 
is zero. This is because at 0 degrees and 180 degrees the mechanical 
movement is at "dead center." The movement of the present invention cannot 
be activated by a linear input when it is in the "dead center" position. 
Either a rotational input or some momentum is required to move the 
rotatable members 18 and 22 off "dead center." However, as the movement 
moves off dead center it is apparent from FIG. 5 that there is a 
sinusoidal variation in the output torque between 0 and 180 degrees. This 
output torque peaks at 90 degrees and because of the positive coupling of 
the present invention, the output torque between 45 and 135 degrees 
remains relatively smooth. Prior art movements of the present type would 
experience a marked decrease in output torque near the 90 degree position, 
as suggested by FIG. 4. However, the positive coupling shown in FIGS. 1 
and 2 tends to smooth out the operation of the mechanical movement of the 
present invention by eliminating wide variations in torque near the 90 
degree position and thereby reducing stress on the shaft 24 and the linear 
input 14. 
The particular form of positive coupling between members 18 and 22 shown in 
FIGS. 1 and 2 is preferred since such a gearing arrangement reduces gear 
tooth load to a minimum level. However, many other types of possible 
couplings and gearing arrangements may be suitable and would fall within 
the scope of the present invention. 
The mechanical movement of the present invention is particularly 
advantageous for use in applications that require approximately 90 degrees 
of rotational movement, such as the operation of the valve shown in FIGS. 
1 and 2. It is evident from FIG. 5 that the torque varies substantially 
between 0 degrees and 45 degrees and between 135 degrees and 180 degrees. 
On the other hand, the torque remains fairly constant between 45 degrees 
and 135 degrees. Thus, one skilled in the art can select a 90 degree range 
of operation to suit the characteristics of the particular device being 
actuated. 
Additionally, it is within the scope of the present invention in 
applications other than that shown in FIGS. 1 and 2, to utilize the gear 
42 as a rotational input to the mechanical movement. In addition to the 
butterfly valve illustrated in FIGS. 1 and 2, the mechanical movement of 
the present invention is equally effective for use as an actuator in ball 
valves, various eccentric valves, and any device requiring approximately 
90 degrees of actuation. 
Accordingly, a mechanical movement has been provided which may be 
manufactured from only a few easily fabricated parts. The mechanical 
movement is quite compact and can operate in a relatively small space. 
Furthermore, the mechanical movement of the present invention is quite 
sturdy and can transmit a substantial amount of force. 
While there has been described what is at present considered to be the 
preferred embodiment of the present invention, it will be obvious to those 
skilled in the art that various changes and modifications may be made 
therein, without departing from the invention, and it is, therefore, aimed 
in the appended claims to cover all such changes and modifications as fall 
within the true spirit and scope of the invention.