Electromechanical screw drive actuator
View Patent ↗An electromechanical linear actuator assembly having in-line axial load support of its screw drive shaft is provided. The bearing support structure provides a single in-line ball bearing accommodated within a hardened end fitting and a screw pivot recess in the axial screw drive shaft. For axial loading in an opposite direction, a number of smaller ball bearings are provided around the outer periphery of the screw shaft in a groove, and are retained within the hardened end fitting by a bearing retainer. End rod support bearings providing heat compensation and lubrication fluid transfer are also provided. A braking mechanism having increased life and more consistent load engagement is also provided. Further, integrated electronics may be provided for position sensing and power efficiency control.
1. A linear actuator, comprising:
a drive screw shaft rotatable by a source of motive power;
a nut threadably engaged on the drive screw shaft for linear translation therealong;
a hollow extension rod drivably coupled to the nut, the extension rod adapted to accommodate the drive screw shaft therein;
an end fitting having a bearing recess therein;
a housing attached to the end fitting and supported upon the end fitting in a fixed relationship thereto; and
a ball bearing seated in the bearing recess;
wherein the drive screw shaft includes a screw pivot recess in a first end thereof sized to accommodate the ball bearing in-line with an axial plane of the drive screw shaft.
2. The actuator of claim 1 , wherein the screw pivot recess, the ball bearing, and the bearing recess are arranged such that axial loading of the screw drive shaft is transferred to the end fitting without being carried by the housing of the actuator.
3. A linear actuator, comprising:
a drive screw shaft rotatable by a source of motive power;
a nut threadably engaged on the drive screw shaft for linear translation therealong;
a hollow extension rod drivably coupled to the nut, the extension rod adapted to accommodate the drive screw shaft therein;
an end fitting having a bearing recess therein;
a ball bearing seated in the bearing recess;
the drive screw shaft including a screw pivot recess in a first end thereof sized to accommodate the ball bearing in-line with an axial plane of the drive screw shaft;
the drive screw shaft further defining a bearing race around its outer periphery in proximity to the first end;
a plurality of ball bearings accommodated in the bearing race; and
a bearing retainer fixably attached to the end fitting, the bearing retainer having an axial groove adapted to accommodate the plurality of ball bearings.
4. The actuator of claim 3 , wherein the bearing race, the plurality of ball bearings, and the axial groove are arranged such that axial loading of the screw drive shaft is transferred to the end fitting without being carried by a housing of the actuator.
5. A linear actuator, comprising:
a drive screw shaft rotatable by a source of motive power;
a nut threadably engaged on the drive screw shaft for linear translation therealong;
a hollow extension rod drivably coupled to the nut, the extension rod adapted to accommodate the drive screw shaft therein;
an end fitting having a bearing recess therein;
a ball bearing seated in the bearing recess;
the drive screw shaft including a screw pivot recess in a first end thereof sized to accommodate the ball bearing in-line with an axial plane of the drive screw shaft;
an extension tube surrounding the screw shaft, the extension tube having an exit end through which the extension rod passes; and
an external bearing support member positioned in proximity to the exit end between an inner surface of the extension tube and an outer surface of the extension rod, the external bearing support member having a spiraled groove in an inner surface thereof.
6. The actuator of claim 5 , wherein the external bearing support member further comprises knurling on an outer surface thereof.
7. The actuator of claim 5 , further comprising an internal rod guide bearing affixed to a second end of the drive screw shaft opposite the first end, the internal rod guide bearing supporting an inner surface of the extension rod, the internal rod guide further including at least one transfer groove therein.
8. The actuator of claim 7 , wherein the internal rod guide is constructed from an acetal resin.
9. The actuator of claim 5 , further comprising an internal rod guide bearing affixed to a second end of the drive screw shaft opposite the first end and in close planar proximity to the external bearing support member, the internal rod guide bearing supporting an inner surface of the extension rod.
10. A linear actuator, comprising;
a drive screw shaft rotatable by a source of motive power;
a nut threadably engaged on the drive screw shaft for linear translation therealong;
a hollow extension rod drivably coupled to the nut, the extension rod adapted to accommodate the drive screw shaft therein;
an end fitting having a bearing recess therein;
a ball bearing seated in the bearing recess;
the drive screw shaft including a screw pivot recess in a first end thereof sized to accommodate the ball bearing in-line with an axial plane of the drive screw shaft; and
the extension rod including a threaded end adapted receive a load end fitting therein.
11. A linear actuator, comprising:
a drive screw shaft rotatable by a source of motive power;
a nut threadably engaged on the drive screw shaft for linear translation therealong;
a hollow extension rod drivably coupled to the nut, the extension rod adapted to accommodate the drive screw shaft therein;
an end fitting having a bearing recess therein;
a ball bearing seated in the bearing recess;
the drive screw shaft including a screw pivot recess in a first end thereof sized to accommodate the ball bearing in-line with an axial plane of the drive screw shaft;
the extension rod including a port in a side wall thereof.
12. A linear actuator, comprising:
a drive screw shaft rotatable by a source of motive power;
a nut threadably engaged on the drive screw shaft for linear translation therealong;
a hollow extension rod drivably coupled to the nut, the extension rod adapted to accommodate the drive screw shaft therein;
an end fitting having a bearing recess therein;
a ball bearing seated in the bearing recess;
the drive screw shaft including a screw pivot recess in a first end thereof sized to accommodate the ball bearing in-line with an axial plane of the drive screw shaft; and
a wrap spring brake member having a shaft wear washer, a brake wear washer, and a brake friction bearing placed therebetween, the brake friction bearing having two contact surfaces each including a spiral groove thereon.
13. The actuator of claim 12 , wherein the brake friction bearing is made from an acetal resin.
14. The actuator of claim 12 , wherein the contact surfaces are angled over at least a portion thereof.
15. The actuator of claim 12 , wherein the shaft wear washer and the brake wear washer each have a bearing contact surface, and where in the bearing contact surface has a surface roughness of between approximately 12 to 150 on the rms scale.
16. A linear actuator, comprising:
a drive screw shaft rotatable by a source of motive power;
a nut threadably engaged on the drive screw shaft for linear translation therealong;
a hollow extension rod drivably coupled to the nut, the extension rod adapted to accommodate the drive screw shaft therein;
an end fitting having a bearing recess therein;
a ball bearing seated in the bearing recess
the drive screw shaft including a screw pivot recess in a first end thereof sized to accommodate the ball bearing in-line with an axial plane of the drive screw shaft;
at least one position sensor positioned in proximity to the extension rod to sense a position thereof, and an electronic controller integrated within a housing of the actuator, the electronic controller using the sensed position from the position sensor to control the source of motive power.
17. The actuator of claim 16 , further comprising a second position sensor positioned in proximity to the extension rod to send position thereof, the two position sensors being axially positioned relative to one another to sense a maximum and a minimum linear position of the extension rod.
18. The actuator of claim 17 , wherein the position sensors are Hall effect limit switches.
19. The actuator of claim 16 , wherein the source of motive power is a double-ended shaft motor, further comprising a brake mechanism operably coupled to a back end of the motor.
20. An axial load support and transfer structure for use in a linear screw drive actuator having a drive screw shaft rotatable by a source of motive power, a nut threadably engaged on the drive screw shaft for linear translation therealong, a hollow extension rod drivably coupled to the nut, and the extension rod adapted to accommodate the drive screw shaft therein, comprising:
an end fitting having a bearing recess therein;
a ball bearing seated in the bearing recess;
wherein the drive screw shaft includes a screw pivot recess in a first end thereof sized to accommodate the ball bearing in-line with an axial plane of the drive screw shaft; and
wherein the drive screw shaft further defines a bearing race around its outer periphery in proximity to the first end;
a plurality of ball bearings accommodated in the bearing race; and
a bearing retainer fixably attached to the end fitting, the bearing retainer having an axial groove adapted to accommodate the plurality of ball bearings.
21. The axial load support and transfer structure of claim 20 , wherein the screw pivot recess, the ball bearing, and the bearing recess are arranged such that axial loading of the screw drive shaft in a first axial direction is transferred to the end fitting without being carried by a housing of the actuator, and wherein the bearing race, the plurality of ball bearings, and the axial groove are arranged such that axial loading of the screw drive shaft in a second axial direction is transferred to the end fitting without being carried by a housing of the actuator.