Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-09-09
2001-07-03
Hoffman, T (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S0400MM, C475S149000
Reexamination Certificate
active
06255751
ABSTRACT:
FIELD OF THE INVENTION
The present invention is generally directed to electric servo actuators and, more particularly, to a compact electric servo actuator having an integrated servo motor and gearhead assembly.
BACKGROUND
Electric servo actuators have many functions and are found in a variety of industrial applications. They are used to control positions, velocities or torques applied to various machine components. Typical applications include machine tools, packaging equipment as well as web processing equipment. Electric servo actuators are selected based upon the design parameters for a particular application. The design parameters that influence the selection process include the torque, rotational speed and power requirements. With respect to electric servo actuator design, it is well known in the art that power is proportional to the product of torque times rotational speed. Using this basic design principle, design engineers can modify the output torque from a servo motor by decreasing the servo motor's output rotational speed.
In practice, gear reducers are often used to convert the high rotational speed of servo motors into a higher torque, lower rotational output speed. Many types of gear reducers are available. One type of gear reducer is a planetary style reducer. This particular style of reducer uses a planetary arrangement of gears to apply a reduction ratio that is in an in-line (concentric) configuration. Planetary gear reducers are generally characterized by their small size, robustness, quiet operation, and low backlash. In typical applications, planetary gear reducers are made in modular form and are mounted to a standard servo motor to achieve the required speed reduction.
FIG. 1
illustrates a typical design configuration having a servo motor
15
operably connected to a gear reducer
16
. As shown in
FIG. 1
, adapter
17
is mounted to output shaft
18
of servo motor
15
. Similarly, pinion
19
attaches to adapter
17
opposite servo motor
15
. Gear reducer
16
receives as input pinion
19
and is selected to produce the desired output torque and rotational speed at shaft
20
.
Conventional design configurations such as those exemplified in
FIG. 1
have several shortcomings. For example, in situations where space and size are of concern, the addition of the components necessary to couple the servo motor with the gear reducer severely limits design options. Conventional configurations address this concern by using right angle gearheads and motors. However, this approach requires additional components and hence leads to a more expensive and heavier system.
Moreover, the conventional approach requires service personnel to manually couple the gear reducer to the servo motor. Often, this process requires special and proprietary mounting methods to fasten the gear reducer to the servo motor. Additionally, the process can result in improper installation or misalignment of the gear reducer with respect to the servo motor's output shaft. For example, if the modular gear reducer is not fastened to the servo motor properly, the strength of the pinion-shaft joint is weakened and can result in premature failure of the components.
Accordingly, there arises a need to provide for an electric servo actuator having substantially the same performance characteristics as a conventional motor and gearhead configuration but with the added feature of being very compact in relation to the conventional approach. Such an electric servo actuator and gearhead configuration would provide greater flexibility with respect to size and space considerations and substantially reduce installation and maintenance costs. The present invention addresses and overcomes the shortcomings of the prior art.
SUMMARY
The present invention generally provides a compact integrated servo motor and gear reducer assembly maintained within a unitary housing. The compact integrated servo motor and gear reducer assembly can be used in applications requiring high torque output but yet with size and/or space limitations. The present servo motor and gear reducer assembly may, for example, also reduce installation and maintenance costs associated with the operation of servo motors and gear reducer assemblies.
In a preferred embodiment of the invention, a servo motor and gear reducer are provided within a unitary housing. The servo motor is supported within the unitary housing at its distal end with bearings near the rear of the unitary housing. At its proximal end, the servo motor is supported with bearings and its output shaft is operatively connected directly to the gear reducer. In a preferred embodiment of the present invention, the gear reducer is a planetary gear system. Hence, the servo motor's output is operatively connected directly to the sun gear of the planetary gear system. In one embodiment, the servo motor rotor and the sun gear may be constructed as a unitary piece (or with the sun gear pressed onto a shaft area of a unitary piece). Furthermore, the bearings supporting the servo motor at its proximal end are contained substantially within and concentric with the planetary gear system. As a result of this configuration, the axial length of the overall assembly is reduced.
In operation, the servo motor rotates the input shaft of the planetary gear reducer, specifically, the sun gear. The output from the planetary gear system is transferred to a planet carrier. The planet carrier has a unitary design and is fully supported with a pair of bearings. As used herein, the term “fully supported” includes large diameter bearings on both sides (e.g., axially) of the planet gears. At least one prior design placed two bearings on the output shaft side of the gear system. However, this leads to planet gears which are supported in a cantilevered fashion. The present invention overcomes this shortcoming by placing bearings on either side of the planet/sun gear system. Also, as noted above, the sun gear bearing is placed axially within the planet carrier bearings.
Another feature of the present invention is that the bearings supporting the servo motor at its distal end are located axially within and concentric with the servo motor's windings. This feature of the present invention further contributes to the compactness of the overall assembly design.
As discussed above, the present invention provides for a compact integrated servo motor and gear reducer assembly contained within a unitary housing. Hence, all of the moving components, including the servo motor, planetary gear system, and support bearings, are contained within the unitary housing. In a preferred embodiment of the present invention, input and output ports are provided to allow for lubrication. As a result of this design, the moving parts of the of the present invention can be lubricated with a simple low pressure oil circulation system. Therefore, the integrated servo motor and gear reducer assembly of the present invention is capable of operating at increased power levels as compared to conventional servo motor and gear reducer assemblies.
Each of the identified features contribute toward a goal of optimizing the power density of the motor in view of cross-sectional constraints. This allows for embodiments, which are constructed in accordance with the principles of the present invention, offering a short axial length given power and diameter requirements.
Therefore, according to one aspect of the invention, there is provided an integrated rotary servo actuator apparatus, comprising: a rotor, having an output shaft; a stator; a planetary gear system, including a sun gear, a plurality of planet gears and an outer ring gear, wherein the sun gear is directly connected to said output shaft and a load shaft is connected to said planet gears; first and second bearings for supporting said planetary gear system, said first and second bearings located on opposing sides of said planetary gear system; and a third bearing for supporting said output shaft, wherein said third bearing is arranged and configured to be axially aligned within
Hoffman T
Merchant & Gould P.C.
Torex Corporation
Waks Joseph
LandOfFree
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