Machine element or mechanism – Mechanical movements – Reciprocating or oscillating to or from alternating rotary
Reexamination Certificate
2000-08-04
2002-04-16
Bucci, David A. (Department: 3682)
Machine element or mechanism
Mechanical movements
Reciprocating or oscillating to or from alternating rotary
C074S608000, C074S089400, C384S015000
Reexamination Certificate
active
06370975
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention:
The present invention relates to an actuator for displacing a table through operation of a drive source to carry out mechanical work such as the conveying of a work-piece, and an actuator system which comprises a plurality of such actuators.
2. Description of the Related Art
There has heretofore been known an actuator having, as a drive source, an electric motor equipped with a sensor such as an encoder, a tachometer generator, or the like for making it possible to control a rotational speed, a drive torque, a stop position, or the like. The rotational motion from the electric motor is converted into linear motion by a drive force transmission shaft such as a ball screw, a trapezoidal screw, or the like, and the linear motion is transmitted to a table mechanism, which is displaced to convey a workpiece.
An electric motor which is incorporated in such an actuator is illustrated in longitudinal cross section in
FIG. 1
of the accompanying drawings. As shown in
FIG. 1
, the electric motor, generally denoted at
1
, has a coupling
4
interconnecting an end of a ball screw
2
and an end of a motor shaft
3
coaxially with each other. The coupling
4
serves to absorb a misalignment between the axes of the motor shaft
3
and the ball screw
2
, and prevent vibrations which are produced when rotary motion is converted into linear motion and also vibrations which are produced due to rotary motion containing a flexural component perpendicular to the axis as the ball screw
2
becomes longer, from being transmitted to the motor shaft
3
.
One end of the ball screw
2
is rotatably supported by a first bearing
5
comprising balls
5
a
which are obliquely interposed between inner and outer races thereof. Since the balls
5
a
bear loads at a certain angle with respect to the axis of the ball screw
2
as indicated by the broken lines in
FIG. 1
, the balls
5
a
are capable of absorbing a load in a direction substantially perpendicular to the axis of the ball screw
2
and also a load in a direction substantially parallel to the axis of the ball screw
2
.
The motor shaft
3
which is housed in a motor housing
6
has an end rotatably supported by a second bearing
7
and a spring washer
8
, and an opposite end rotatably supported by a third bearing
9
, which is of a double bearing configuration.
The first bearing
5
supports the ball screw
2
in both axial and radially inward directions. The second bearing
7
supports the motor shaft
3
in a radially inward direction for thereby absorbing vibrations and inertial forces that are generated in a radially outward direction by the rotational forces of the motor shaft
3
. The third bearing
9
supports the motor shaft
3
in both axial and radially inward directions. Therefore, in the case where a photosensor P is mounted in the electric motor
1
for detecting the number of revolutions, the rotational speed, or the like of the electric motor
1
, it is possible to position an encoder disk D fixedly mounted on the motor shaft
3
accurately within a clearance A in the photosensor P.
The electric motor
1
which tends to experience a relatively high temperature during operation suffers the problem of different thermal expansions due to different materials and shapes of the parts used. Typically, the motor housing
6
is made of an aluminum-base material for heat radiation, and the motor shaft
3
is made of an iron-base material. The difference between different thermal expansions of the materials of the motor housing
6
and the motor shaft
3
causes the motor housing
6
to be displaced axially, possibly concentrating stresses on the second bearing
7
which supports the motor shaft
3
. Consequently, it is necessary to absorb the difference between these different thermal expansions in some way.
In the conventional electric motor
1
, the spring washer
8
is interposed between balls
7
a
of the second bearing
7
and an inner wall surface of a bracket
6
a
of the motor housing
6
. The difference between the different thermal expansions can be absorbed when the spring washer
8
is elastically deformed, pressing the balls
7
a
in a direction substantially parallel to the axis of the motor shaft
3
.
Actuators for making rotary and linear motion, such as an electric actuator represented by an electric motor and a fluid pressure actuator represented by a fluid cylinder, are controlled by a motor driver and a solenoid-operated valve. These actuators, which include actuators for use in robots, are usually disposed independently of, not integrally with, a controller.
If the electric motor
1
is incorporated as an actuator in an apparatus (not shown), thus providing a drive source, it is necessary to reduce the size and weight of the actuator as much as possible in order to increase the versatility of the actuator.
The coupling
4
which interconnects the motor shaft
3
and the ball screw
2
may bring about resonance in the motor shaft
3
and the ball screw
2
when rotated. When the electric motor
1
, which requires high dynamic characteristics, as with a servomotor, resonates, the positional control accuracy thereof is lowered, and its dynamic characteristics are impaired. If the coupling
4
, which-serves to prevent vibrations from being applied to the motor shaft
3
, were dispensed with and the motor shaft
3
and the ball screw
2
were integrally coupled directly to each other in order to alleviate the above drawbacks, then unwanted vibrations would be transmitted to the motor shaft
3
. As a result, it would be difficult to convey a workpiece continuously stably.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an actuator which allows the operator to select various actuator configurations depending on the environment in which the actuator is to be installed and the application in which the actuator is to be used.
According to a first aspect of the present invention, there is provided an actuator comprising a frame extending linearly for a predetermined length, a plurality of covers detachably and selectively mounted on respective side surfaces of the frame, a drive source, a table mechanism disposed on the frame for displacement in an axial direction of the frame in response to operation of the drive source, and drive force transmitting means for transmitting drive forces from the drive source to the table mechanism.
The covers may include a pair of side covers mounted on transverse side surfaces, respectively, of the frame, a pair of end covers mounted on longitudinal ends, respectively, of the frame, and a top cover engaging upper surfaces of the end covers. The drive force transmitting means may comprise at least a ball screw shaft or a timing belt.
The actuator may further comprise a cylinder disposed axially parallel to and outside of the frame, the cylinder having a piston rod coupled to the table mechanism.
The actuator may further comprise a cylinder disposed axially in the frame, the cylinder comprising a cylinder tube and a piston displaceable in the cylinder tube, the piston having a magnet, the table mechanism including a movable table having an inner wall surface held in sliding contact with an outer circumferential surface of the cylinder tube, the inner wall surface supporting a magnet thereon. The cylinder may comprise one or a plurality of parallel cylinders extending axially along the frame.
The actuator may further comprise a drive control block which houses at least an electric motor, a speed detecting mechanism for detecting a rotational speed of the electric motor, a brake mechanism associated with the electric motor, and a clutch mechanism associated with the electric motor. The drive control block may be composed of a plurality of blocks housing the electric motor, the speed detecting mechanism, the brake mechanism, and the clutch mechanism, respectively, the blocks being detachably coupled together.
Another object of the present invention is to provide an actuator having an electric motor including a motor s
Nagai Shigekazu
Suzuki Masahiko
Bucci David A.
Joyce William C
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
SMC Kabushiki Kaisha
LandOfFree
Actuator and actuator system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Actuator and actuator system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Actuator and actuator system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2858228