Machine element or mechanism – Mechanical movements – Reciprocating or oscillating to or from alternating rotary
Reexamination Certificate
1999-09-15
2001-06-26
Herrmann, Allan D. (Department: 3682)
Machine element or mechanism
Mechanical movements
Reciprocating or oscillating to or from alternating rotary
C254S103000
Reexamination Certificate
active
06250170
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention pertains to a load directing trunnion mount for a linear actuator that is constructed to receive all of the tensile forces exerted on the actuator shaft or lead screw of the linear actuator. In this manner, the load directing trunnion mount relieves a transmission drive element (for example, a drive gear or a sprocket or pulley) and the transmission housing enclosing the drive element from tensile forces exerted on the actuator shaft during use of the linear actuator.
(2) Description of the Related Art
A linear actuator of the type with which the present invention is concerned is basically a mechanism that converts rotational movement into linear movement. The mechanism includes a drive assembly that can be controlled to selectively rotate a screw threaded shaft or lead screw of the actuator in opposite directions. The drive assembly typically includes a motor, for example an electric motor, and a transmission coupling the motor output shaft to the lead screw. The transmission assembly can be a gearing assembly, a sprocket and chain assembly or a belt and pulley assembly. The linear actuator also includes a nut assembly that is mounted on the lead screw of the actuator for linear movement of the nut assembly along the lead screw in response to rotation of the lead screw. By rotating the lead screw in opposite directions of rotation, the nut assembly moves in opposite linear directions along the length of the lead screw.
FIG. 1
shows one operative environment of a linear actuator of the type described above. It is emphasized that the particular use made of the linear actuator in
FIG. 1
is illustrative only. Linear actuators of the type shown are used in a variety of different environments where it is desired to convert reciprocating rotary movement to reciprocating linear movement.
FIG. 1
is a schematic representation of a cross section through a supporting frame of an adjustably elevating exercise treadmill of the prior art. The figure shows a cross section through a frame member
12
of the treadmill frame that supports the running deck (not shown) of the treadmill. The right-hand end of the frame member
12
is shown broken away, but the right-hand end of the frame member would rest on the supporting surface
14
on which the exercise treadmill is placed. The left-hand end or the elevating end of the treadmill frame is supported on a pair of bell cranks
16
, only one of which is shown in FIG.
1
. The bell cranks
16
are mounted to opposite frame members
12
of the frame by a pivot shaft
18
. One arm
22
of each bell crank extends downwardly from the pivot shaft
18
to a cylindrical roller
24
mounted on the distal end of the arm. The roller
24
supports the forward or left-hand elevating end of the treadmill frame on the support surface
14
. The second arm
26
of each bell cranks extends upwardly from the pivot shaft
18
. The distal end of each second arm
26
is mounted by a pivot connection
28
to a nut assembly
32
mounted on the lead screw
34
of the linear actuator. The nut assembly
32
can have internal screw threading that is complementary to the external screw threading of the lead screw, or can be a recirculating ball type nut assembly or other type of nut assembly commonly employed with linear actuators of this type. The lead screw
34
is mounted for rotation inside a transmission housing
36
by a pair of bearings mounted in opposite walls of the transmission housing. The transmission housing
36
contains a transmission mechanism that includes a drive element, for example a gear, sprocket or pulley, that is secured to the lead screw
34
for rotation therewith. The drive element is driven by the transmission contained in the transmission housing
36
which in turn is driven by an electric motor
38
. Exercise treadmills of this type commonly have controls (not shown) that can control the electric motor
38
to drive the transmission and ultimately the lead screw
34
in opposite directions of rotation. By controlling the rotation of the lead screw
34
in two directions, linear movement of the nut assembly
32
across the lead screw
34
is also controlled. The linear movement of the nut assembly
32
across the lead screw
34
controls pivoting movement of the bell cranks
16
about their pivot shaft
18
which in turn controls elevating movement, of the left-hand end of the treadmill shown in FIG.
1
. For example, operation of the electric motor
38
to rotate the lead screw
34
causing the nut assembly
32
to move to the left as viewed in
FIG. 1
will result in the bell cranks
16
rotating in a counterclockwise direction about its pivot shaft
18
and thus elevating the left-hand or forward end of the treadmill frame shown in FIG.
1
. Controlling the electric motor
38
to rotate the lead screw
34
in the opposite direction causing the nut assembly
32
to move to the right as shown in
FIG. 1
will cause the bell cranks
16
to move in a clockwise direction about their pivot shaft
18
resulting in the lowering of the treadmill frame shown in FIG.
1
.
Transmission housings
36
of the type shown in
FIG. 1
are commonly connected to the frame members
12
of the treadmill by a pivot pin
42
extending through a hole in a flange or flanges
44
of the transmission housing and a hole in a flange
46
mounted on the treadmill frame. When a load is placed on the treadmill, for example, by a jogger on the treadmill, the load is transmitted through the bell crank
16
to the lead screw
34
as a tensile force on the lead screw. This tensile force exerted on the lead screw
34
is transmitted to the transmission housing
36
and ultimately to the flanges
44
of the transmission housing that are connected by the pivot pin
42
to the flange
46
of the frame.
FIG. 2
shows a detailed view of a prior art linear actuator of the type employed in a treadmill such as that shown in FIG.
1
. In
FIG. 2
, like parts of the linear actuator described in reference to
FIG. 1
have the same reference numbers.
FIG. 2
shows a distal portion
52
of the lead screw that extends outside the transmission housing
36
and has the nut assembly
32
mounted thereon. An opposite proximal portion
54
of the lead screw extends into the transmission housing
36
.
FIG. 3
is a partial view showing the prior art transmission housing
36
in cross section and the proximal portion
54
of the lead screw mounted in the transmission housing as well as the drive element mounted on the lead screw proximal portion.
Referring to
FIG. 3
, the transmission housing has a first end wall
56
with a first shaft opening
58
passing therethrough. An opposite second end wall
62
, shown to the left in
FIG. 3
, encloses an interior volume
64
of the transmission housing with the first end wall
58
. A cylindrical recess
66
is formed into the second end wall
62
. The recess
66
is concentric with the first opening
58
through the housing first end wall
56
. The proximal portion
54
of the lead screw extends through the first opening
58
of the housing and into the cylindrical recess
66
of the housing second end wall
62
. Beginning at the right hand end of the lead screw proximal portion
54
shown in
FIG. 3
, the proximal portion is mounted for rotation in the first opening
58
by a bearing or bushing
68
mounted in the opening. A circular washer
70
is then mounted on the proximal portion
54
of the lead screw. The washer
70
seats against the bushing
68
and an annular shoulder
72
formed in the interior of the transmission housing first end wall
56
. A thrust bearing
74
is then mounted on the lead screw proximal portion
54
seating up against the washer
70
. The drive element is then mounted on the lead screw proximal portion
54
. In
FIG. 3
, the drive element is a gear
76
, but the drive element could be a sprocket for a chain drive or a pulley for a belt and pulley drive, depending on the particular transmission employed. The gear
76
has a circular recess
78
fo
Evertowski Mark S.
Hill Jason J.
Emerson Electric Co.
Herrmann Allan D.
Howell & Haferkamp L.C.
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