This invention relates to linear drive actuators, and more particularly to portable, compact linear drive actuators.
Linear driver actuators used with portable hand tools commonly include a hydraulic cylinder coupled to an internal or external gas or electricity powered hydraulic pump. The hydraulic cylinder and pump require periodic inspections and maintenance. Also, the hydraulic cylinder and pump limit the size of the actuator.
Linear drive actuators are desirable because they are compact and lightweight. Unfortunately, they use roller screws that need lubrication and produce heat.
It is an object of the present invention to provide a durable, lightweight, compact and versatile linear drive actuator that uses a roller screw as the mechanical linear drive mechanism.
It is another object of the present invention to provide a linear drive actuator that uses a roller screw with greater lubrication and heat dissipating features.
Disclosed herein is a linear drive actuator that includes an improved linear drive mechanism that uses a solid or hollow, threaded roller screw shaft with a low clearance, high capacity roller bearing, herein after called a thrust bearing, integrally formed or shaped on its proximal end. An inner race with a plurality of non-helical grooves is formed on the proximal end of the shaft. Disposed longitudinally and axially around the inner race is a plurality of parallel rollers that include a plurality of teeth. Disposed around the rollers is a cylindrical outer race with a set of non-helical grooves configured to mesh with the teeth on the rollers.
Mounted over the distal end of the roller screw shaft is a roller screw nut. The roller screw nut includes an outer race, a plurality of grooved rollers axially aligned inside the outer race, and an inner race. When the roller screw shaft is rotated, the roller screw nut moves axially over the roller screw shaft. A hollow extension tube longitudinally aligned with the roller screw shaft and configured to axially move with the roller screw nut.
Surrounding and covering the roller screw housing and the extension tube is a closed main housing configured to be filled with lubricating fluid. The extension tube is sufficient in length, so its distal end extends from the distal end of the main housing and connects to an end termination or a tool implement.
The proximal end of the roller screw shaft connects to a drive axle from a gearbox assembly located in a gearbox housing. The gearbox housing is attached to a motor housing containing at least one primary motor. Located adjacent to the motor housing is a volume compensator housing with an internal filling cavity. A sealing piston divides the filling cavity into a lubricating holding chamber filled with a lubricant fluid and an air chamber that communicates with atmospheric air.
The gearbox housing and motor housing include fluid passages that allow lubricating fluid to flow back and forth through the main housing and into and around the roller screw shaft and the elongated tube. During operation, lubricating fluid flows through the motor housing, through the gearbox housing, through the roller screw shaft, through the extension tube and into the main housing. During operation, the axial movement of the nut body and the extension tube changes the volume of the main housing which causes lubricating fluid to flow back and forth between the lubricating holding chamber and the main housing. The lubricating fluid further acts as a heat transfer media which conducts heat away from the gearbox, the motors, the thrust bearing and roller nut to the main housing where the heat can-be readily conducted to the external environment, cooling the system.
Disclosed herein in
The improved linear drive mechanism 100, (shown in
Mounted on the screw shaft 102 is a thrust bearing retainer plate 112 aligned over the distal opening formed on a gearbox housing 61 that houses a multiple gear and torque sensing system 60.
Mounted over the section distal end of the screw shaft 102 is a roller screw nut 136. The roller screw nut 136 includes an outer race, a plurality of grooved rollers axially aligned inside the outer race 138, and an inner race 140. When the roller screw shaft 102 is rotated, the roller screw nut 136 moves axially over the screw shaft 102. A hollow extension tube 145 is longitudinally aligned with the screw shaft 102 and configured to axially move with the roller screw nut 136. Attached to the distal end of the roller nut 137 is a hollow, elongated extension tube 145
Surrounding and covering the roller screw housing 137 and the extension tube 145 is a closed main housing 150. The extension tube 145 is sufficient in length so its distal end extends from the distal end opening on a main housing 150 and connects to a terminating end element of a tool implement (not shown).
As shown more clearly in
During assembly, the motors 50, 55 are axially aligned in the motor mounts 48, 49, respectively, so the drive shaft 52 on each motor 50 extends through the transverse plate 45. A pinion gear 54 is attached to each drive axle 52. Formed on the transverse plate 45 is at least one fluid hole 47 that allows the lubricating fluid 300 to flow back and forth through the transverse plate 45. In one embodiment, the drive shaft on the primary electric motor 50 is connected to pinion gear in the gearbox housing. Surrounding the pinion gear is a coaxially carrier ring with an appropriate number of equal size planet gears mounted thereon. The planet gears include teeth that mesh with exterior teeth on the pinion gear. Surrounding the carrier ring is a coaxially aligned outer ring gear with inner teeth that mesh with teeth on the planet gears. The outer ring gear is fixed relative to the pinion gears so the carrier ring and the pinion gears rotate inside the outer ring gear. The gear ratio of the roller screw shaft 20 to the primary electric motor 160 and the pinion gear is approximately 1:5 but can vary over a wide range depending on the final application of the liner drive actuator 10.
Positioned in front of the motor assembly bracket 41 is a multiple gearbox assembly and torque sensing system 60. The gearbox assembly 60 includes a gear box housing 61 with a distal end opening 62 and a proximal end opening 64. Formed inside the gear box 61 housing is a gear cavity 65 configured to receive the multiple gear system 68. Attached to the distal end opening 62 is a thrust bearing retainer plate 120.
The multiple gear system 68, shown in
The second and third stage ring gear sleeve and flange 73 is supported radially and axially by the gearbox housing 61 but may rotate within the gearbox housing 61. It is supported in the circumferential direction (rotationally) by a plurality of coil springs 76 which progressively compress as the output torque of the system increases. The deformation of these coil springs 76 results in the progressive rotation of the second and third stage ring gear sleeve and flange 74, the second stage ring gear 78 and the cylindrical extension elements 80. Cylindrical extension elements 80 are positioned to apply a normal force to profile incorporated into the inner surface of friction brake element 84. The rotation of these extension elements 80 in response to the output torque of the gearbox provides the control feedback for the system thus acting as a torque sensing system. In the current embodiment, the progressive rotation of control profile 91 relative to the stationary external gearbox housing 61 is used to open or close a control switch (not shown) for the secondary motor 55.
The internal surface of the cylindrical extension element 80 bears upon a profile or cam shape 85 on the interior surface of the friction brake element 84. The cylindrical extension element 80 rotates progressively along with all the other components in response to the deformation of the coil spring supports 76. Prior to the application of the ring gear brake, when the output force of the actuator 10 is low, the cam shape 85 is positioned so a control switch (not shown) is closed and the secondary motor 55 is activated which causes the ring gear 70 to rotate, reducing the gear ratio from the primary motor 50 to the output drive pins 71. The output speed of the gearbox 60 decreases as the actuator's internal drive torque and overall output force increases.
Located in front of the gear box housing 61 is an improved linear drive mechanism 100 that includes a hollow roller screw shaft 102 with a wide cylindrical inner race 126. Attached to the front or distal end of the gear box housing 61 is a end cap 115. Formed inside the end cap 115 is an inner cavity 66 that forms the outer race 122 to holds a separately inserted outer race 122. During assembly, the proximal end of the screw shaft 102 is inserted into the closed cavity. Disposed between the outer race 122 and the inner race 126 are a plurality of rollers 130. In combination, the screw shaft 102, outer race 122, the inner race 126 and rollers 130 form a thrust bearing similar too the low clearance high capacity roller bearing disclosed in U.S. patent application Ser. No. 15/523,620, filed on May 1, 2017, now incorporated by reference.
The screw shaft 102, shown more clearly in
The inner race 126 is integrally formed on the proximal end of the screw shaft 102. As shown in
The roller screw nut 134 is similar to the geared planetary roller screw shown in U.S. Pat. No. 2,683,379 (Strandgren) which is now incorporated herein. The roller screw nut 134, shown in
When the screw shaft 102 is rotated, the roller nut 134 moves longitudinally over the screw shaft 102. Formed on the distal end of the roller nut 134 is a recessed circular groove 139 that receive a tab 149 formed on the proximal end of the extension tube 145 to securely connect the nut body 137 to the extension tube 145.
As mentioned above, and shown in
The linear drive actuator 10 includes a lubricating and cooling system 220 used to continuously lubricate and cool the actuator during operation. The system 220 includes volume compensation housing 222 located adjacent to the motor assembly 40 and opposite the multiple gearbox and torque sensing system 60. The volume compensation housing 222, shown in
Extending into the proximal end opening 226 is an end cap 228 that includes an end plate 230 and a cylindrical body 232 that extends perpendicularly from the inside surface of the end plate 230. The inside void area in the cylindrical body 232 forms a filling cavity 234. An o-ring 237 is mounted between the inside surface of the volume compensation housing 222 and the outside surface of the cylindrical body 232 to form a water tight seal.
Located inside the filling cavity 234 a transversely aligned piston 240 that divides the filling cavity 234 into a rear air chamber 242 and a front lubricant holding chamber 246. An air hole 244 is formed on the end plate 230 which connects the air chamber 242 to the atmosphere. The piston 240 is configured to slide inside the cylindrical body 232. An o-ring 248 is placed between the outer edge of the piston 240 and the inside surface of the cylindrical body 232 to create a watertight seal.
Between the intermediate wall and the piston 240 is a coil spring 250 configured to create a rearward biasing forcing on the piston 240.
Dispensing into the lubricating holding chamber 246 is a lubricating fluid 300, such as mineral oil. Formed on the intermediate wall is a fluid hole 260 that enables lubricating fluid 300 to flow into the lubricant holding chamber 246. Formed on the front plate 224 is a fluid hole 225
During operation, the piston 240 moves longitudinally inside the filling cavity 234 in response to differences in pressure between the atmosphere and the pressure exerted on the lubrication volume created by movement of the roller nut bearing housing and the extension tube 145 discussed further below.
During assembly, lubricating fluid 300 is poured into the lubricating holding chamber 246 formed in the volume compensation housing 222. Lubricating fluid 300 then flows into the front cavity 228 of the volume compensation housing 222 around the primary and secondary motors 55, 60 through the motor bracket and into the gearbox cavity. The lubrication fluid 330 then flows around the thrust bearing 120, around the screw shaft 102 and into the roller screw bore 108. The lubrication fluid 300 then flows into the extension tube 145. The entire system is closed so that when the volume for the lubricating fluid 300 inside the extension tube 145 changes, lubricating fluid 300 flows back and forth between the filling cavity and the extension tube 145 according to pressure differences between the atmosphere and the extension tube 145. For example, when the extension tube 145 is extended, the volume for the lubricating fluid 300 inside the extension tube 145 is increased which draws lubricating fluid 300 from the lubrication fluid chamber 246 into the motor bracket, through the gearbox housing 61, into and around the screw shaft 102. The piston 240 moves so atmospheric air 200 is drawn into the air chamber 24. When the extension tube 140 is retracted, the volume for lubricating fluid 300 inside the extension tube 145 is reduced which causes lubricating fluid 300 to flow back into the lubrication fluid chamber 246. Air inside 320 the air chamber 242 is forced outward. The piston moves to accommodate the changes of volume of the lubricating fluid 300 in the chamber 246.
In compliance with the statute, the invention described has been described in language more or less specific as to structural features. It should be understood, however, that the invention is not limited to the specific features shown, since the means and construction shown comprises the preferred embodiments for putting the invention into effect. The invention is therefore claimed in its forms or modifications within the legitimate and valid scope of the amended claims, appropriately interpreted under the doctrine of equivalents.
This invention has application in the tools and machinery industry. More specifically, in industries that require linear drive activators and roller screws and roller bearings.
This utility patent application is based on and claims the filing date benefit of U.S. provisional patent application (Application 62/480,183) filed on Mar. 31, 2017.
Filing Document | Filing Date | Country | Kind |
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PCT/US18/25760 | 4/2/2018 | WO | 00 |
Number | Date | Country | |
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62480183 | Mar 2017 | US |