ROTARY ACTUATOR

TECHNICAL FIELD

The present invention relates generally to the field of rotary actuators, and more specifically to high performance small size rotary actuators.

BACKGROUND ART

Several types of rotary actuators are generally known. For example, vane-based rotary hydraulic actuators have been produced as well as purely electric motor based rotary actuators.

BRIEF SUMMARY OF THE INVENTION

With parenthetical reference to the corresponding parts, portions or surfaces of the disclosed embodiment, merely for the purposes of illustration and not by way of limitation, provided is a rotary actuator (100) having a reference structure (110), an output member (113) arranged for rotary movement relative to the reference structure about an axis, a first linear motor (116) having a first member (119) and a second member (122), the first linear motor configured and arranged to selectively apply an output force urging the first member and the second member apart along a generally linear direction, the first linear motor first member coupled to the reference structure, the first linear motor second member coupled to the output member and configured and arranged to cause a torque between the output member and the reference structure in a first direction about the axis when the first linear motor applies the output force, a second linear motor (131) having a first member (134) and a second member (137), the second linear motor configured and arranged to selectively apply an output force urging the second linear motor first member and the second linear motor second member apart along a generally linear direction, the second linear motor first member coupled to the reference structure, and the second linear motor second member coupled to the output member and configured and arranged to cause a torque between the output member and the reference structure in a direction about the axis opposite the first direction when the second linear motor output force is applied.

The first linear motor (216) may comprise a single acting hydraulic motor. The first linear motor first member may have a prismatic chamber and/or the first linear motor second member may have a piston (222). The prismatic chamber may be a cylinder (219). The first linear motor may have a piston link (248) arranged between the piston and the output member. The first linear motor first member may be rigidly mounted to the reference structure. The piston link and/or the piston may be connected through a ball joint. The piston link and the output member may be connected through a pivot joint (228) or pin joint. The first linear motor and the second linear motor may each have a direction of action which may be generally parallel. The output member may have a shaft. The output member may have a first pivot bearing (228) coupled to the first motor second member and/or a second pivot bearing (240) coupled to the second motor second member. The first pivot bearing and the second pivot bearing may be separated by an offset in a dimension parallel to the axis.

The first pivot bearing, the second pivot bearing, and the axis may be collinear. The first linear motor first member may have a cylinder and the first linear motor second member may have a piston, the piston having a first surface and a second surface. The first surface may form a first chamber (245) with the cylinder and the second surface form a second chamber (255) with the cylinder. The cylinder may have a generally cylindrical surface. The cylindrical surface may have a hole between the piston first surface and the piston second surface. The rotary actuator may further have a drive link coupled to the piston. The drive link may traverse the hole.

The second linear motor (231) may have a single acting hydraulic motor. The first linear motor and the second linear motor may have an equivalent hydraulic fluid volume displaced for a given linear motor linear distance of actuation. The first linear motor and the second linear motor may be hydraulically balanced. The output member may be coupled to an aircraft control surface. The rotary actuator may further have a position sensor configured and arranged to measure an angle between the output member and the reference structure. The rotary actuator may further have a servo controller.

In another aspect, provided is an actuator (300) for rotating a shaft (313) about an axis (319), which has: a housing (303), a first single acting cylinder (322) disposed in the housing and having a first piston (328) and a first connecting link (349) therein, a crank (334) attached to the shaft, a second single acting cylinder (325) disposed in the housing and having a second piston (331) and a second connecting link (349) therein, in which the first and second connecting links may be attached to different locations on the crank, and in which the actuator is configured and arranged such that actuation of the first acting cylinder causes the crank to rotate in a first direction and actuation of the second single acting cylinder causes the crank to rotate in a second direction opposite the first direction.

The first and second cylinders may be oriented substantially parallel. The first and second cylinders may be both configured and arranged to each have a pre-load to provide a force in the same general direction to remove a backlash. The shaft may rotate on a set of bearings disposed in the housing. The shaft may be connected to an aircraft control surface. The actuator may be configured and arranged to move the crank from a first position to a second position by applying an additional pressure to one of a first pressure chamber and a second pressure chamber. The actuator may be configured and arranged to be able to maintain a position of the crank by providing a substantially equal pressure inside the first and second pressure chambers.

The actuator may be configured and arranged to maintain a position of the crank by not allowing hydraulic fluid to flow in or out of the first or second pressure chambers. The first and second single acting cylinders may have a cross section which may be not circular. The first connecting link may be connected to the first piston through a ball joint (352). The first connecting link and the output member may be connected through a pivot joint or pin joint. The first and second single acting cylinders may be separated by an offset in a dimension parallel to the axis. The first and second single acting cylinders may share a common bore. The actuator may be configured and arranged such that the first single acting cylinder expels a substantially equal volume of hydraulic fluid to a volume of hydraulic fluid drawn in by the second single acting cylinder for a movement of the shaft. The actuator may further have a position sensor arranged and configured to measure an angle between the shaft and the housing. The actuator may further have a servo controller.

In another aspect, provided is a method of operating an actuator having a reference structure (110), an output member (113) arranged for rotary movement relative to the reference structure about an axis, a first linear motor (116) having a first member (119) and a second member (122), the first linear motor configured and arranged to selectively apply an output force urging the first member and the second member apart along a generally linear direction, the first linear motor first member coupled to the reference structure, the first linear motor second member coupled to the output member and configured and arranged to cause a torque between the output member and the reference structure in a first direction about the axis when the first linear motor applies the output force, a second linear motor (131) having a first member (134) and a second member (137), the second linear motor configured and arranged to selectively apply an output force urging the second linear motor first member and the second linear motor second member apart along a generally linear direction, the second linear motor first member coupled to the reference structure, the second linear motor second member coupled to the output member and configured and arranged to cause a torque between the output member and the reference structure in a direction about the axis opposite the first direction when the second linear motor output force may be applied, having the steps of: causing the first linear motor to apply a first non-zero force and the second linear motor to apply a second non-zero force, whereby a backlash may be reduced.

The method may further have the steps of: receiving a commanded output member characteristic, and adjusting the first non-zero force relative to the second non zero force when the output member has an actual characteristic which does not match the commanded output member characteristic. The output member characteristic may be an angle relative to the reference structure. The method may further have the step of increasing the second non-zero force relative to the first non zero force when the output member has an angle less than the commanded output member angle position, whereby a torque may be applied between the output member and the reference structure.

In another aspect, provided is a hydraulic actuator (400) having a cylinder (419) having a generally cylindrical shaped inner surface with a longitudinal axis and a first end and a second end, the inner surface having a hole (470) arranged between the first end and the second end, a piston (422) configured and arranged for sliding movement within the cylinder, the piston having a first surface and a second surface, the first surface and the second surface facing generally opposite directions along the longitudinal axis, the first surface forming a first chamber (494) with the cylinder and the second surface forming a second chamber (495) with the cylinder, a first hydraulic port (492) in fluid communication with the first chamber, a second hydraulic port (493) in fluid communication with the second chamber, a drive link (448) having a first end and a second end and arranged to pass through the hole, the drive link first end coupled to a position on the piston between the first surface and the second surface, in which the actuator may be configured and arranged to cause a movement of the drive link relative to the cylinder when the piston moves relative to the cylinder.

The drive link does not pass through the first chamber or the second chamber. The hydraulic actuator may further have a reference structure and a pivot joint between the drive link and the reference structure configured and arranged to allow a rotary movement between the drive link and the reference structure about an axis. The cylinder may be mounted to the reference structure. The hydraulic actuator may further have a drive shaft (413) configured and arranged for rotary movement relative to the cylinder. The drive shaft may be coupled to the drive link. The cylinder may have a non-circular cross section. The drive link may be coupled to the piston through a pivot or pin joint. The drive link may be coupled to the piston through a universal joint. The drive link may be coupled to the piston through a ball joint. The first chamber and the second chamber may be hydraulically balanced.

The actuator may be configured and arranged such that the first chamber expels a substantially equal volume of hydraulic fluid to a volume of hydraulic fluid drawn in by second chamber for a movement of the piston relative to the cylinder. The hydraulic actuator may further have a position sensor configured and arranged to measure an angle between the drive link and the cylinder. The hydraulic actuator may further have a servo controller.

In another aspect, provided is an actuator power system having a bent axis hydraulic pump (740) having a first hydraulic port (733), a second hydraulic port (735), and an input drive shaft, a gear assembly (750) having a gear shaft mechanically coupled to the bent axis pump input drive shaft for providing a mechanical advantage to cause the bent axis pump to rotate at a lower speed than the gear shaft, in which the actuator power system may be configured and arranged to cause a fluid flow between the first hydraulic port and the second hydraulic port when the gear shaft may be rotated. The actuator power system may further have an electric motor (760) coupled to the gear shaft. The actuator power system may further have a hydraulically balanced rotary actuator configured and arranged to be powered from the bent axis hydraulic pump.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a first embodiment of the rotary actuator.

FIG. 2 is a side view of a second embodiment of the rotary actuator.

FIG. 3 is a perspective of a third embodiment of the rotary actuator.

FIG. 4 is a front view of the rotary actuator shown in FIG. 3.

FIG. 5 is a side view of the rotary actuator shown in FIG. 3.

FIG. 6 is a perspective view of the embodiment shown in FIG. 3 with its case removed.

FIG. 7 is a front view of the embodiment shown in FIG. 6.

FIG. 8 is a side view of the embodiment shown in FIG. 6.

FIG. 9 is an elevational view of a piston and connecting rod assembly of the rotary actuator shown in FIG. 6.

FIG. 10A is a cross-sectional view taken along lines 10A-10A in FIG. 9.

FIG. 10B is an exploded perspective view of a portion of the assembly shown in FIG. 10A.

FIG. 11 is a side section view of a fourth embodiment of the rotary actuator taken along lines 11-11 in FIG. 12.

FIG. 12 is a front view of the fourth embodiment of the rotary actuator.

FIG. 13 is a perspective view of the piston assembly of the rotary actuator shown in FIG. 12.

FIG. 14 is a side section view of the piston assembly shown in FIG. 13.

FIG. 15 is an enlarged view of the circular dashed section shown in FIG. 14.

FIG. 16 is a front view of a fifth embodiment of the rotary actuator.

FIG. 17 is a side section view of the rotary actuator shown in FIG. 16.

FIG. 18 is an isometric view of an alternative piston assembly.

FIG. 19 is a top view of the alternative piston assembly shown in FIG. 18.

FIG. 20 is a side view of the alternative piston assembly shown in FIG. 18.

FIG. 21 is a side section view of the alternative piston assembly shown in FIG. 18.

FIG. 22 is a side view of another embodiment of the rotary actuator with its case removed.

FIG. 23 is a system diagram of a rotary actuator system.

FIG. 24 is a section view of a first version pump shown in FIG. 23.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate.

The disclosed embodiments provide high performance rotary actuators and rotary actuator systems, which are driven by linear motors. Referring now to the drawings, and more particularly to FIG. 1, a side view of a first embodiment of the rotary actuator is disclosed. Rotary actuator 100 includes reference structure 110, first linear motor 116, second linear motor 131, and output member 113. As shown in FIG. 1, reference structure 110 is generally a rigid frame or housing. Output member 113 is also a generally rigid structure. Output member 113 is coupled to reference structure 110 through pivot joint 114. Pivot joint 114 allows rotary movement between reference structure 110 and output element 113 about axis 115. (Axis 115, as shown in FIG. 1, has a direction perpendicular to the page.) Pivot joint 114 may also contain a sensor which measures the angle and/or torque between reference structure 110 and output member 113.

Linear motor 116 has two main parts which include first member 119 and second member 122. First member 119 and second member 122 are coupled for linear movement relative to one another. When linear motor 116 is activated, a force is applied urging first member 119 and second member 122 apart along direction 160.

Linear motor 131 is similar to linear motor 116. Linear motor 131 has two main parts, first member 134 and second member 137. First member 134 and second member 137 are coupled for linear movement relative to one another. When linear motor 131 is activated, a force is applied urging first member 134 and second member 137 apart along direction 163.

First member 119 of linear motor 116 is coupled to reference structure 110 at coupling 125. Second member 122 is coupled to output member 113 at coupling 128. Couplings 125 and 128 may include a pivot joint, universal joint, or ball joint. Couplings 125 and 128 may also be a rigid mounting if a portion of first member 119 and second member 122 are able to rotate relative to each other. The actuation of linear motor 116 urges second member 122 to be driven rightwards relative to first member 119 along line 160. This actuation effectively urges coupling 125 and coupling 128 apart. Stated another way, linear motor 119 causes a force to be applied between reference structure 110 at point 125 and output member 113 at point 128 in a direction that urges the two apart. Because coupling 128 is above line 165 formed between coupling 125 and pivot joint 114, the force applied by linear motor 116 causes torque 169 between reference structure 110 and output member 113.

Linear motor 131 is similarly connected between reference structure 110 and output element 113, however, linear motor 131 is arranged to selectively cause a torque 166 to be applied between reference structure 110 and output element 113 which has a direction opposite torque 169. More specifically, first member 134 of linear motor 131 is coupled to reference structure 110 at coupling 143. Second member 137 is coupled to output member 113 at coupling 140. Couplings 143 and 140 may include a pivot joint, universal joint, ball joint, or may also be a rigid mounting if a portion of first member 134 and second member 137 are able to rotate relative to each other. The actuation of linear motor 131 urges second member 137 to be driven rightwards relative to first member 134. This actuation effectively urges coupling 143 and coupling 140 apart. Stated another way, linear motor 131 causes a force to be applied between reference structure 110 at point 143 and output member 113 at point 140 in a direction that urges the two apart. Because pivot joint 140 is below line 167 formed between coupling 143 and pivot joint 114, the force applied by linear motor 131 causes torque 166 between reference structure 110 and output member 113.

Because pivot joint 140 is below the line 167, compared to pivot joint 128 which is above the line 165, the torques 166, 169 applied by each respective linear motor are in opposite directions. Linear motors 116 and 131 only need to be able to produce a force in a single direction between reference structure 110 and output element 113. There is no need for linear motors 116 and 131 to be able to provide a force in both directions, i.e. both “pushing” and “pulling”. It is only necessary that linear motors 116 and 131 are arranged to cause opposite direction torques to be applied between reference structure 110 and output member 113. While only a single acting linear motor is necessary for rotary actuator 110, dual acting linear motors can be used in rotary actuator 110 without departing from the spirit of the invention. Also, linear motors 116 and 131 can be replaced with single acting linear motors which both only provide a “pulling” force instead of a “pushing” force, since the motors would still be able to produce opposite torques.

Linear motors 116 and 131 may be electrical motors, single acting hydraulic actuators, pneumatic actuators, linear drive screw, or any other similar motor type. Rotary actuator 110 may also include a servo controller.

Rotary actuator 100 can be operated in multiple different operational modes. A first method of operation is a low backlash mode. In the low backlash mode, a minimum threshold force is always applied by each linear motor 116, 131 while rotary actuator 100 is in use. Under this mode, because the mechanical linkages of the system are always under compression, any tolerance or “play” in joints 114, 125, 128, 140, and 143 will be “forced to one side” of their region of “play” and effectively prevented from causing a backlash. For example, if rotary actuator 100 is first commanded to apply a clockwise torque to output member 113 and then subsequently apply a counterclockwise torque, because the mechanical linkages in rotary actuator 100 are always in compression, significant backlash will not occur. More specifically, in order to apply clockwise torque 169 to output member 113, linear motor 116 may be commanded to apply 20 N of force while linear motor 131 is commanded to apply a minimum threshold force of 10 N. A force of 10 N is thus being counteracted between the motors, and this 10 N of counteraction force is passed through the mechanical linkage between the motors. Because each element of rotary actuator 100 is therefore under compression caused by the counteraction force, none of the joints of rotary actuator 100 will be free to “jiggle.” Next, when rotary actuator 100 is commanded to apply a counterclockwise torque 166, linear motor 116 is commanded to apply the minimum threshold force of 10 N while linear motor 131 is commanded to apply a force of 20N. This causes the net torque on output member 113 to shift from clockwise to counterclockwise while all of the joints of rotary actuator 100 remain in compression. A typical prior art rotary actuator which has a single dual acting motor is not capable of maintaining all joints of its mechanical linkage in compression when switching between applying clockwise and counterclockwise torques, and therefore suffers from backlash when individual mechanical linkage joints switch from being in compression and tension.

Rotary actuator 100 can also be operated in a low friction mode, in which only one motor is active at a time. By preventing continuous tension in the mechanical linkage which is present in the low backlash mode of operation, the friction experienced by the individual linkage joints is reduced. The low friction mode of operation helps reduce wear rates of the joints and linear motors. Also, because each motor is not continuously on, efficiency increases may also be realized with the low friction mode compared to the low backlash mode of operation.

It is also possible to selectively adjust the mode of operation of rotary actuator 100 depending upon a particular need of the system at a given time.

FIG. 2 is a side partial section view of a second embodiment rotary actuator. Rotary actuator 200 includes major components of reference frame 210, first single acting hydraulic motor 216, second single acting hydraulic motor 231, and output member 213. Rotary actuator 200 is arranged to drive driven member 250, which is rigidly coupled to output member 213.

First hydraulic motor 216 has cylinder 219 and piston 222. Cylinder 219 is rigidly mounted to reference frame 210. Piston 222 is configured and arranged within cylinder 219 to allow piston 222 to slide left and right within cylinder 219, while maintaining a seal between the outer surface of piston 222 and the inner cylindrical wall of cylinder 219. Piston 222 and cylinder 219 form chamber 245, which is in fluid communication with hydraulic port 246. Piston 222 has a pivot joint 247, which is coupled to the left end of connecting link 248. The right end of connecting link 248 is coupled to output member 213 through pivot joint 228.

Output member 213 is coupled to reference structure 210 through pivot joint 214, which allows output member 213 to rotate relative to reference structure 210 about axis 215. Pivot joint 214 has rotary position sensor 217, which senses the angle between reference structure 210 and output member 213 and outputs this angle information on output line 218. Driven member 250 is rigidly coupled to output member 213 and pivot joint 214 such that driven member 250 rotates together with output member 213 relative to reference structure 210.

Second hydraulic motor 231 has cylinder 234, which is rigidly mounted to reference frame 210, and piston 237. Piston 237 is configured and arranged within cylinder 234 to allow piston 237 to slide left and right within cylinder 234, while maintaining a seal between the outer surface of piston 237 and the inner cylindrical wall of cylinder 234. Piston 237 and cylinder 234 form chamber 255, which is in fluid communication with hydraulic port 256. Piston 237 has a pivot joint 257, which is coupled to the left end of connecting link 258. The right end of connecting link 258 is coupled to output member 213 through pivot joint 240.

Hydraulic fluid is provided by ports 246 and 256 to single acting linear hydraulic motors 216 and 231 respectively. The output force produced by linear motors 216 and 231 is directly dependent upon the pressure of the fluid in ports 246 and 256 respectively. The pressure in ports 246 and 256 can be controlled with standard hydraulic valves.

The operation of rotary actuator 200 is substantially similar to rotary actuator 100. More concretely, hydraulic motors 216 and 231 both produce “pushing” forces between reference structure 210 and output member 213 which respectively cause torques of opposite polarity to be applied between reference structure 210 and output member 213. Similarly, in the operation of rotary actuator 100, motors 119 and 131 produce opposite torques between reference structure 110 and output member 113. Also, rotary actuator 200 can be operated in a low backlash mode and low friction mode similar to the modes of operation for the rotary actuator 100.

The dimensions of linear hydraulic motors 216 and 231 are substantially the same. More specifically, the cross sectional area of cylinder 219 is substantially the same as the cross sectional area of cylinder 234. These dimensions cause a volume of hydraulic fluid to flow in through port 246 when piston 222 is displaced rightwards to be equivalent to the volume that flows into port 256 for an equivalent rightwards displacement of piston 237. When rotary actuator 200 is “centered”, meaning piston 222 is displaced by an equivalent amount as piston 237, rotation of output member 213 causes a rightwards displacement of piston 222 which is substantially equivalent to the leftwards displacement of piston 237. This characteristic of “balanced displacement” of rotary actuator 200 has significant positive implications for the overall hydraulic system used to drive rotary actuator 200. Because the total hydraulic volume actively in the hydraulic system, excluding the hydraulic reservoir, will remain generally constant in a system having only “balanced displacement” actuators such as rotary actuator 200, the efficiency of the system is significantly improved. Compared to a non-balanced hydraulic system, the work potential of high pressure fluid is not lost each time the total in system hydraulic volume decreases.

Turning to FIGS. 3-10, and initially to FIG. 3, third embodiment rotary actuator 300 has a housing 303 that is formed with a main body 306 that surrounds a shaft 313 (best shown in FIGS. 6 and 8). The shaft 313 may be mounted on bearings (not shown) at opposite ends and may be provided with an output member 316 that may be integrally formed or attached to the shaft 313 such that the output member 316 rotates about the central longitudinal shaft axis 319. The housing 303 also includes two cylinders 322 and 325 extending from main body 306. Cylinders 322 and 325 define chambers for pistons 328, 331 (shown in FIGS. 6 and 8). Pistons 328 and 331 have a circular cross-section suitable for use in the cylinders 322 and 325. Cylinders 322 and 325 in this embodiment are single acting hydraulic cylinders as described in greater detail below. It will be understood by those of ordinary skill in the art based on this disclosure that the term cylinder is used to describe the barrel of a linear motor and is not intended to be limited to any specific shape and other shapes of chambers for receiving different shaped pistons would also be suitable. For example, cylinder may refer to a barrel with a non-circular cross section, or a barrel with generally prismatic shape. The cylinders 322 and 325 have longitudinal axes 323, 324 respectively that are disposed on opposite sides of the shaft axis 319 as best shown in FIG. 4.

In FIG. 6, housing 303 has been removed for clarity to show the arrangement of pistons 328 and 331. Pistons 328 and 331 are connected to crankpins 334 and 337 disposed on opposite sides of the central longitudinal shaft axis 319. Accordingly, downward movement of piston 328 causes the shaft 313 to rotate counterclockwise about axis 319 relative to the orientation of FIG. 6 and downward movement of piston 331 causes the shaft 313 to rotate clockwise about axis 319 relative to the orientation of FIG. 6. As best shown in FIG. 5, the cylinders 322 and 325 may be mounted at different positions along the length of the shaft 313. Additionally, as best shown in FIG. 4, pistons 322 and 325 may be staggered or offset 327 from each other.

Piston 328 has a substantially flat surface 340 at first end 343 that forms an end wall of the pressure chamber when piston 328 is installed inside cylinder 322. Cylinder 322 is single acting as the portion of the chamber adjacent to surface 340 is the only part exposed to working fluid. Accordingly, piston 328 only has to be sealed with respect to one pressure chamber, and piston 328 and connecting rod 349 are not sealed at second end 346. Connecting rod 349 is attached to piston 328 by a ball and pin structure 352 that is described in greater detail below. Legs 362, 365 of the connecting rod 349 are connected to crankpin 334 on shaft 313 as described in greater detail below. Piston 331 has a flat surface 332 and is installed in cylinder 331 and connected to crankpin 337 by connecting rod 349 in the same manner as piston 328.

Turning to FIG. 9, piston 328 and connecting rod 349 are shown in greater detail. Top surface 340 of piston 328 is exposed to the working fluid. Piston 328 has rings 350, 353 for sliding, sealing engagement inside the cylinder as known to those of ordinary skill in the art. Connecting rod 349 has a pair of legs 362, 365 extending downward and slightly outward to second ends 357, 358. Legs 362, 365 have openings 363, 366 disposed therethrough for receiving the crankpins 334 or 337. Openings 363, 366 are typically provided with bearing surfaces 367 (FIG. 10A) such as bushings or the like as will be known to those of ordinary skill in the art. Turning to FIG. 10A, connecting rod 349 is connected to piston 328 by pin 356 mounted inside a ball 359. Connecting rod 349 has an opening 354 for receiving the ball 359. The ball 359 has a central opening for receiving the pin 356. The piston 328 has a central axial opening 329 for receiving the first end 351 of the connecting rod 349 and has a pair of transverse openings 364, 368 disposed on opposite sides of piston 328 for receiving the pin 356 in the transverse direction (indicated by arrow 369) relative to the piston axis 370. Pin 356 is disposed through the opening in the ball 359 and through transverse openings 364, 368 in piston 328 and is secured in position by a connecting member 373. As best shown in FIG. 10B, the connecting member 373 has body 375 with flange 377 at one end 379 and has a cap 381 with a flange 383 at one end 385. When the two parts of the connecting member 373 are attached, the flanges 377, 383 prevent the pin 356 from sliding out of the ball 359 and the transverse openings 364, 368 in the piston 328. Body 375 of the connecting member 373 has elongate sections 387 extending in the direction of the longitudinal axis 388. Elongate sections 387 have a reduced width section 389 located toward the distal end 390. The reduced width sections 389 extend to fingers 391 that have the same width as the remainder of the elongate sections 387 for a section 392 and then an angled section 393 terminating at the distal end 390. Cap 381 has a cylindrical portion 393 with openings 396 disposed around the circumference. A ring 397 is formed on the opposite side of the openings 396 and the ring 397 terminates at a distal end 399.

Hollow pin 356 is installed through transverse openings 364, 368 in the opposite sides of piston 328 and through ball 359 and is secured by placing the body 375 of connecting member 373 through the pin 356 and attaching cap 381 to distal end 390 of body 375. When cap 381 is being engaged with body 375, fingers 391 deflect inward and then snap into openings 396 and ring 399 fits into reduced width section 389 on body 375.

The ball and pin structure 352 described above provides mechanical advantage and reduces the size and weight of connecting rod 349 and pin 356. Pin 356 transmits the force received from the pressure chamber into ball 359, and ball 359 transmits the force from pin 356 into crankshaft 313. Use of ball 359 instead of a pivot joint allows an additional degree of freedom useful in releasing stress from any misalignment.

Other structures for joining the connecting rod 349 to the piston 328 may also be suitable as will be evident to those of ordinary skill in the art.

The first, second, and third embodiments provide several surprising advantages. Rotary actuators 100, 200, and 300 have the advantage of being able to be selectively operated in a low backlash mode, which provides a higher degree of precision in controlling an output member. Additionally, since the low backlash mode operation is optional, precision operation can be substituted with a low wear mode of operation.

Additionally, rotary actuators 100, 200, and 300 have the advantage of being balanced hydraulic actuators. More specifically, in a balanced hydraulic actuator system an equivalent amount of hydraulic fluid enters the expanding chambers as volume of fluid that is exiting the shrinking chambers. Having a fluid and force balanced actuator system allows for multiple advantages. Balanced hydraulic systems provide greater hydraulic pump efficiency. Additionally, hydraulic pumps such as a bent axis hydraulic pump which are more suited for balanced hydraulic operation can be used. Further, balanced forces allow for the design of simpler servo controllers because the servo control algorithms and hydraulic pressure control valves do not need to account for a right/left force differential.

Rotary actuators 100, 200, and 300 also have the advantage of having a very thin envelope. More specifically, as shown in FIG. 7, the horizontal width of rotary actuator 300 is much smaller than comparable prior art systems. Since cylinders 328 and 331 are staggered and offset from each other, a thin actuator envelope is achieved that is not possible if the cylinders 328, 331 are not staggered and offset. Additionally, because each piston connecting rod 349 in rotary actuator 300 has a double leg (FIG. 6, 362 & 365) pivot joint connection, and a high surface area, ball joint (352), very high forces can be applied without damaging the joints, which in turn allow for a shorter lever arm and thin envelope.

Additionally, since the linear actuators only need to be single acting they provide lower part counts, lower cost, and simpler design in comparison to prior art double acting linear actuators. The single acting linear motors used in actuators 100, 200, and 300 also provide the advantage of having a low hydraulic leakage rate. More specifically, prior art double action hydraulic pistons typically have a piston link which passes through a high pressure chamber which acts upon one side of the piston. Such prior art systems require a high pressure seal across the piston link surface, which are problematic to design and maintain, and often result in significant leakage. Because the only high pressure seals in the disclosed embodiments are between the piston outer surface and the cylinder inner surface, there is not a high level of hydraulic fluid leakage as would occur in a prior art piston link seal.

FIGS. 11-15 provide views of a fourth embodiment of the rotary actuator. FIG. 11 is a side cross section view of rotary actuator 400 taken along section line 11-11 in the front view FIG. 12. As shown in FIGS. 11-12, rotary actuator 400 includes housing 410, output shaft 413, cylinder 419, piston 422, connecting link 448, and slide bearing 447. FIG. 11 also shows left end plate 490 and right end plate 491. End plate 490 has been removed in FIG. 12.

Housing 410 is formed of a rigid non-permeable material such as cast iron, steel, composite, high strength plastic, or other similar material. Housing 410 provides a surface for bolting or mounting actuator 400 to a reference structure. Cylinder 419 is formed as a through-bore of housing 410. Cylinder 419 has a generally hollow cylindrical shape with first end 471 and a second end 472. Approximately halfway between first end 471 and second end 472 the upper wall of cylinder 419 has hole 470.

Piston 422 is arranged and configured for sliding engagement within cylinder 419. As shown in FIG. 11, piston 422 has a generally cylindrical shape with a generally rectangular prism shaped region 401 cut into the cylinder. More specifically, as shown in the orientation of FIG. 11, piston 422 has the general shape of a cylinder arranged on its side. Piston 422 has a left vertical circular end surface 473 which has a diameter substantially similar to the inside diameter of cylinder 419. Following a clockwise outer perimeter of cylinder 422, the upper edge of surface 473 connects to horizontal cylindrical surface 475. Horizontal cylindrical surface 475 has ridges facing cylinder 419 and is configured for holding seals between piston 422 and cylinder 419. Such seals are ring shaped and made from Teflon or some other similar material. Cylindrical surface 475 extends rightwards to connect to annular vertical surface 476. Annular vertical surface 476 extends downwards to flat horizontal surface 477. Flat horizontal surface 477 extends rightwards to connect to semi cylindrical surface 478 which has a cylindrical axis oriented perpendicular to the page as shown in FIG. 11. Surface 478 extends first downwards, then rightwards, and back upwards to flat horizontal surface 479. Surface 479 is parallel and in the same plane as surface 477. Surface 479 extends rightwards into annular vertical surface 480. Annular surface 480 has an outer diameter. This outer diameter is substantially equal to the diameter of cylinder 419. Surface 480 extends upwards to connect to horizontal cylindrical surface 481. Horizontal cylindrical surface 481 also has ridges facing cylinder 419 and configured for holding seals. Surface 481 extends rightwards to vertical circular surface 474. Surface 474 extends downward and connects back to cylindrical surface 481 at 482. As shown in FIGS. 11, 481 and 482 are pointing to the same cylindrical surface cut by the section plane. The surface pointed at by 481 and 482 are also the same surface as pointed to at 475 and 483. The surface at 482 extends leftwards to 483. The surface at 483 makes contact with the lower end of vertical circular surface 473, completing a clockwise perimeter walk around piston 422.

Passing through the central region of cylindrical surface 478 is vertical through-bore 485. Arranged in close tolerance within cylindrical surface 478 is cylindrical slide bearing 447. Slide bearing 447 is free to slide against piston surface 478 in two degrees of freedom including lateral sliding into and out of the page (as oriented in FIG. 11) and also rotation about the axis of cylindrical surface 478.

Slide bearing 447 is a generally cylindrical shape with its cylindrical axis coaxial with the cylindrical axis of surface 478. Slide bearing 447 has cylindrical through-bore 486, which holds lower end 448a of rod shaped connection link 448 in sliding engagement. More specifically, link 448 is able to slide relative to slide bearing 447 along line 487. Connecting link 448 extends through hole 470 where it connects with output member 413, and continues extending its upper end 448b into chamber 403. Chamber 403 is defined by an upper wall of housing 410, end plates 490 and 491, and upper wall of cylinder 419. Chamber 403 is in fluid communication with hole 470, region 401, and fluid port 499 which is arranged in the upper wall of housing 410.

Output member 413 is arranged spanning hole 470 and is coupled to pivot joint 414. Pivot joint 414 allows output member 413 to rotate relative to housing 410 about an axis 415 directed perpendicular to the page as shown in FIG. 11. Output member 413 has cylindrical through-bore 488 which forms a sleeve around link member 448 holding link 448 in tight non-moving engagement. Pivot joint 414 is also coupled to link 448, causing movement of link 448 to be limited to rotary movement about axis 415.

Arranged on left and right ends of cylinder 419, and attached to housing 410, are end plates 490 and 491 respectively. Hydraulic port 492 passes through end plate 490 to connect to chamber 494 which is formed by cylinder 419 and piston surface 473. Similarly, hydraulic port 493 passes through end plate 491 to connect to chamber 495 which is formed by cylinder 419 and piston surface 474. Around upper end 448b of link 448 is slide bearing 447′. Slide bearing 447′, which is substantially similar to slide bearing 447, is only shown for demonstrative purposes in FIGS. 11-15. This embodiment does not have slide bearing 447′, but FIGS. 11-15 show how easily slide bearing 447′ can be added together with a second piston symmetrical to piston 422 in chamber 403.

FIGS. 13-15 show views of the piston assembly shown in FIG. 11, including piston 422, connecting link 448, pivot joint 414, and slide bearing 447. Note that in FIGS. 13-15 connecting link 448 is in a vertical orientation, whereas in FIGS. 11 and 12, connecting link 448 is in a rotated configuration.

Comparing the changes from FIG. 11 to FIG. 15, it can be observed how slide bearing 447 has rotated counter clockwise, and that connecting link lower end 448a has slid downwards relative to slide bearing 447, penetrating into bore hole 486.

Rotary actuator 400 generally operates by adjusting the hydraulic pressures in ports 492 and 493 to cause piston 422 to move leftwards or rightwards, which in turn causes connecting link to act as a rotating lever, which then causes output link 413 to also rotate.

As an example, we consider rotary actuator 400 being in a state as shown in FIG. 11 in which it is desired to rotate output member 413 counter clockwise. First, ports 492 and 493 would be connected to hydraulic control lines, housing 410 would be mounted on a reference structure, and output shaft/link 413 would be connected to a member to be rotationally driven. The hydraulic pressure in port 492 would then be increased while the hydraulic pressure in port 493 is decreased. This causes the pressure in chamber 494 to increase, and the pressure in chamber 495 to decrease. When the pressure in chamber 494 falls below the pressure in chamber 495, a net rightwards force is effectively applied on piston 422. More concretely, the pressure placed by the fluid in chamber 494 applies a rightwards force on circular surface 473. A similar leftwards force is created by the pressure in chamber 495 on circular surface 474. Since the pressure in 494 is greater than 495, the rightwards force is greater than the leftwards force, resulting in a net rightwards force applied to piston 422. This force is effectively mediated on piston 422 through housing 410 and endplates 490 and 491.

The rightwards force on piston 422 is communicated as a rightwards force on lower end of connecting link 448a through slide bearing 447. Because connecting link 448 is rigidly coupled to output shaft 413, and because link 448 and output shaft 413 are coupled to pivot joint 414, connecting rod 448 can only move as a rotation about pivot joint 414. The rightwards force applied to connecting link 448 causes connecting link 448 to act as a lever with a fulcrum at pivot joint 414. Therefore, the rightwards force applied by piston 422 is converted into a counterclockwise torque on connecting link 448 which is then passed to output shaft 413.

As piston 422 slides rightwards relative to housing 410, connecting link 448 rotates counterclockwise relative to housing 410. As connecting link 448 rotates counterclockwise, the bottom end 448a of link 448 must slide downwards relative to sliding bearing 447. In other words, since link bottom end 448a must travel in an arc relative to pivot joint 414, the vertical height of bottom end 448a relative to piston 422 must change as the angle of rotation of connecting link 448 changes. Also, as connecting link 448 rotates counterclockwise relative to housing 410, slide bearing 447 must also rotate counterclockwise relative to piston 422 since connecting link 448 is encircled in low tolerance by slide bearing 447.

If there is any error in the alignment between the connecting link 448, piston 422, and cylinder 419, slide bearing 447 is free to slide into or out of the page as shown in FIG. 11 in order to relieve such misalignment. For example, if cylinder 419 is not perfectly orthogonal to the plane that connecting link 448 rotates in, such as if the right end of cylinder 419 tilts slightly up out of the page, slide bearing 447 will be able to slide upwards/downwards as piston 422 moves left and right in order to maintain unstrained contact with connecting link 448.

Because the cross section of cylinder 419 is the same on the left side of piston 422 as on the right side of piston 422, the volume of fluid which must flow in through port 492 must be equal to the volume of fluid flowing out of port 493 for a rightwards movement of piston 422. Thus, rotary actuator 400 is a balanced hydraulic actuator.

The seals arranged between piston 422 and cylinder 419 at 475 and 481, prevent high pressure from chambers 494 and 495 from passing into regions 401 and 403. Thus, the output shaft 413 does not come into contact with any high pressure chamber. Port 499 is used to supply oil which may be needed to lubricate output shaft 413 and connecting link 448, or to drain any oil which leaks across the seals between piston 422 and cylinder 419.

FIGS. 18-21 show a variation of rotary actuator 400 having a second version piston assembly 505 in which cylindrical slide bearing 447 is replaced with ball slide bearing 547. FIG. 18 is a perspective view of second version piston assembly 505 showing piston 522, holding ball slide bearing 547, which embraces connecting link 548. FIG. 19 is a top view of assembly 505 showing the arrangement of the ball slide bearing 547 in piston 522. FIG. 20 is a side view of piston assembly 505, and FIG. 21 is a sectional side view taken along line 21-21 in FIG. 19. As shown in FIG. 21, ball slide bearing 547 is held in two dimensional rotary engagement to piston 522 through race 507. Race 507 is held in piston 522 by a flanged annular end stop 506. Ball slide bearing 547 allows the lower end 548a of connecting link 548 to linearly slide in and out of the central through-bore of the ball slide bearing 547.

Ball slide bearing 547 operates very similarly to cylindrical slide bearing 447 in rotary actuator 400. However, as viewed in FIG. 21, instead of providing a degree of freedom into and out of the page relative to the piston like slide bearing 447, ball slide bearing 547 provides two degree of freedom, rotary movement between ball slide bearing 547 and piston 522. This second degree of freedom relieves any misalignment of connecting link 548 in which connecting link 548 is not perfectly arranged in the plane of the page shown in FIG. 21.

FIGS. 16-17 show another embodiment of the rotary actuator that is similar to rotary actuator 400 but having four cylinders and four pistons. FIG. 16 is a top view of actuator 600 with end plates removed showing parallel cylinders 619a, 619b, 619c, and 619d. FIG. 17 is a side cross section view taken along line 17-17 in FIG. 16. As shown in FIG. 17, pistons 622a and 622b are arranged in respective cylinders 619a and 619b. Piston 622a and piston 622b are substantially symmetrical about the axis of pivot joint 614. When a clockwise torque is desired on output shaft 613, piston 622a is driven rightwards while piston 622b is driven leftwards. The hydraulic ports driving pistons 622a and 622b may or may not be hydraulically coupled. If they are hydraulically coupled, hydraulic phasing will be easier. If they are not hydraulically coupled, while phasing may be more difficult, the system will be redundant if one of the piston-cylinder pairs is hydraulically compromised. While not shown, pistons 622c and 622d are planar symmetric to pistons 622a and 622b. All four pistons are coupled to output shaft 613.

The embodiments 400 and 600 have several surprising advantages over prior art rotary actuator systems. Rotary actuators 400 and 600, like actuators 100, 200, and 300 have the advantage of being balanced hydraulic actuators. For example, with reference to FIG. 11, as piston 422 moves rightwards, the volume of fluid entering chamber 494 is substantially equal to the volume of fluid exiting chamber 495. In a prior art double acting piston which has a piston rod passing through one chamber, the volume of fluid entering/exiting the piston rod side chamber would be less than the fluid exiting/entering the non piston rod chamber due to the cross sectional area of the piston rod. Additionally, the cross sectional area of the piston rod would cause the force that is applied to a piston for a given hydraulic pressure to be different on the side of the piston without the piston rod. Because rotary actuator 400 has no piston rod which passes through chambers 494 or 495, the magnitude of force applied to piston 422 for a given pressure in chamber 494 is equivalent to the opposite force which would be applied by chamber 495 placed at an equivalent pressure. Having a fluid and force balanced actuator system allows for multiple advantages. Balanced hydraulic systems provide greater hydraulic pump efficiency. Additionally, hydraulic pumps such as a bent axis hydraulic pump which are more suited for balanced hydraulic operation can be used. Further, balanced forces allow for design of simpler servo controllers because the servo control algorithms and hydraulic pressure control valves do not need to account for a right/left force differential.

Additionally, rotary actuators 400 and 600 have the advantage of having a thin profile and low part count as found in actuators 100, 200, and 300. A thin profile allows these actuators to be used in thin wing aircraft designs or other environments requiring a thin profile.

As shown in FIG. 22, multiple rotary actuators 300 can be combined to drive the same output member 316 in order to achieve a high drive torque, or a fault tolerant/redundant system. The actuators 300 are shown with their housing removed for clarity. The actuator shafts 313 of the two actuators 300 are connected such that the shafts 313 of the two actuators 300 form a single unit that can be acted on by all four pistons simultaneously.

FIG. 23 shows an actuator system 700, which includes one or more rotary actuators 720 and an electro hydraulic bent axis pump system 730. System 700 also includes hydraulic reservoir 725 and servo valve system 722. Pump 730 is specifically designed for efficient operation in a balanced hydraulic system.

FIG. 24 provides a side section view of electro hydraulic bent axis pump system 730. Pump system 730 includes the major components of bent axis pump 740, gear box 750, electric motor 760, and housing 731, which holds each of the other components together. Pump system 730, when driven, creates a pressure differential and fluid flow between hydraulic port 733 and 735.

Bent axis pump 740 contains piston heads 737a and 737b which are connected to piston links 738a and 738b respectively. Piston heads 737a and 737b are arranged within a pump body supported by bearings 739. Piston links 738a and 738b are coupled to rotor 744, which is suspended by bearings 741.

Gear box 750 contains gears 751, 752, and 753. Gears 751, 752, and 753 are held in housing 731. Gearbox 750 is mechanically coupled to rotor 744. Motor 760 has output shaft 761 which is coupled to gear box 750. Motor 760 also has stator 762 and rotor 763. Gear box 750 is configured to provided a mechanical advantage which causes bent axis pump rotor to rotate at a speed lower than motor shaft 761.

Pump system 730 is particularly suited to use with balanced hydraulic actuators. Because bent axis pump 740 only has two ports, it is particularly suited to balanced hydraulic actuators which would not cause a need for a third hydraulic port for increasing or decreasing the hydraulic fluid volume of the system. Further, the use of the gear box providing a mechanical advantage allows for prolonged pump system lifetimes, which is particularly appropriate for aircraft applications.

The particular embodiments shown may also be combined with a servo controller. A standard servo controller can be used to control the linear motors to adjust their force or position output based upon a commanded output member torque/position and a measured output member torque/position.

Therefore, while the presently-preferred form of the rotary actuator, rotary actuator system, and method of operating a rotary actuator are disclosed and described, and several modifications discussed, persons skilled in this art will readily appreciate that various additional changes may be made without departing from the scope of the invention.

ROTARY ACTUATOR

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CPC

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