WO2020123833A1

WO2020123833A1 - Humanoid lower body robot electro hydrostatic actuating ankle

Info

Publication number: WO2020123833A1
Application number: PCT/US2019/066023
Authority: WO
Inventors: David Geiger
Original assignee: Moog Inc.
Priority date: 2018-12-14
Filing date: 2019-12-12
Publication date: 2020-06-18

Abstract

A robotic ankle comprising a lower leg and a foot configured to rotate about a pitch axis and a roll axis, first and second electric motors, first and second hydraulic pumps driven by the respective motors, first and second hydraulic piston assemblies hydraulically connected to the respective pumps and each comprising a housing and an actuating rod connected to a piston separating first and second chambers in the housing, one of the housing or the actuating rod connected to the lower leg and the other of the housing or the actuating rod connected to the foot, and the first and second hydraulic piston assemblies configured to actuate the foot relative to the lower leg about the pitch axis and about the roll axis, whereby rotation of the foot relative to the lower leg about the pitch axis and about the roll axis is controllable by the first and second motors.

Description

HUMANOID LOWER BODY ROBOT

ELECTRO HYDROSTATIC ACTUATING ANKLE

TECHNICAL FIELD

[0001] The present disclosure relates generally to the field of humanoid robotic joints, and more particularly to an electro hydrostatic actuated humanoid robotic ankle joint.

BACKGROUND ART

[0002] Humanoid robots are known in the prior art. Such robots are provided with joints designed to allow for the robot to move in a manner resembling human movement. For example, U.S. Patent No. 9,327,785, entitled“Humanoid Robot Implementing a Ball and Socket Joint,” is directed to a humanoid robot ankle joint comprising two elements connected by a spherical joint with three degrees of freedom in rotation, the joint being moved by three actuators each acting in one of the three degrees of freedom.

BRIEF SUMMARY

[0003] With parenthetical reference to the corresponding parts, portions or surfaces of the disclosed embodiment, merely for purposes of illustration and not by way of limitation, an improved robotic ankle (16) is provided comprising: a lower leg member (18); a foot member (19); an ankle joint (20) between the lower leg member and the foot member; the ankle joint having an ankle center (23); the foot member configured to rotate about a pitch axis (24) extending through the ankle center and to rotate about a roll axis (25) extending through the ankle center; a first electric motor (31 A) adapted to be supplied with a current and to operatively provide a torque on a first output shaft (40A); a first hydraulic pump (32A) driven by the first output shaft of the first electric motor; a first hydraulic piston assembly (33A) hydraulically connected to the first hydraulic pump and comprising a first housing (34A) having a first chamber (35A) and a second chamber (36A), and a first piston (37A) separating the first and second chambers of the first housing; a first actuating rod (38 A) connected to the first piston and configured to move linearly with the first piston relative to the first housing; one of the first housing or the first actuating rod connected to the lower leg member and the other of the first housing or the first actuating rod connected to the foot member; the first hydraulic piston assembly configured to actuate the foot member relative to the lower leg member within a range of motion about the pitch axis; a second electric motor (31B) adapted to be supplied with a current and to operatively provide a torque on a second output shaft (40B); a second hydraulic pump (32B) driven by the second output shaft of the second electric motor; a second hydraulic piston assembly (33B) hydraulically connected to the second hydraulic pump and comprising a second housing (34B) having a first chamber (35B) and a second chamber (36B), and a second piston (37B) separating the first and second chambers of the second housing; a second actuating rod (38B) connected to the second piston and configured to move linearly with the second piston relative to the second housing; one of the second housing or the second actuating rod connected to the lower leg member and the other of the second housing or the second actuating rod connected to the foot member; the second hydraulic piston assembly configured to actuate the foot member relative to the lower leg member within a range of motion about the pitch axis; the first hydraulic piston assembly and the second hydraulic piston assembly configured to actuate the foot member relative to the lower leg member within a range of motion about the roll axis; whereby rotation of the foot member relative to the lower leg member about the pitch axis and about the roll axis is controllable by the first electric motor and the second electric motor.

[0004] The first electric motor may be a variable speed bidirectional electric motor adapted to operatively provide a torque on the first output shaft at varying speeds and by direction, the second electric motor may be a variable speed bidirectional electric motor adapted to operatively provide a torque on the second output shaft at varying speeds and by direction, the first hydraulic pump may be a reversible variable speed hydraulic pump, the second hydraulic pump may be a reversible variable speed hydraulic pump, and rotation of the foot member relative to the lower leg member about the pitch axis and about the roll axis may be controllable by adjusting the speed and/or direction of the first variable speed bidirectional electric motor and the speed and/or direction of the second variable speed bidirectional electric motor. The first electric motor may comprise a brushless DC servo-motor and the second electric motor may comprise a brushless DC servo-motor. The first hydraulic pump may be selected from a group consisting of a fixed displacement pump, a variable displacement pump, a two-port pump, and a three-port pump.

[0005] The first piston may comprise a first surface area exposed to the first chamber of the first housing and a second surface area exposed to the second chamber of the first housing, and the second piston may comprise a first surface area exposed to the first chamber of the second housing and a second surface area exposed to the second chamber of the second housing, and the first surface area may be substantially equal to the second surface area. The first housing may comprise a cylinder having a first end wall, the piston may be disposed in the cylinder for sealed sliding movement therealong, and the first actuator rod may be connected to the piston for movement therewith and may comprise a portion sealingly penetrating the first end wall.

[0006] The robotic ankle may comprise a controller (50, 50A, 50B) that receives input signals and outputs command signals to the first electric motor and/or the second electric motor to control rotation of the foot member relative to the lower leg member about the pitch axis and about the roll axis. The robotic ankle may comprise a regenerative power stage (56A, 56B) to the first electric motor and/or the second electric motor and the first electric motor and/or the second electric motor may be controlled by the controller to operate in a regeneration mode. The robotic ankle may comprise an electric storage device (55, 55A, 55B) connected to the first electric motor and/or the second electric motor.

[0007] The controller (50) may output command signals to the first electric motor and the second electric motor to control rotation of the foot member relative to the lower leg member about the pitch axis and about the roll axis. The robotic ankle may comprise a first regenerative power stage (56A) to the first electric motor and a second regenerative power stage (56B) to the second electric motor and the first electric motor and the second electric motor may be controlled by the controller (50) to operate in a regeneration mode. The robotic ankle may comprise an electric storage device (55) connected to the first electric motor and the second electric motor. The robotic ankle may comprise a first position sensor (51 A) configured to sense a position of the first piston and to provide an input signal to the controller (50), and a second position sensor (5 IB) configured to sense a position of the second piston and to provide an input signal to the controller (50).

[0008] The robotic ankle may comprise a first controller (50A) that receives input signals and outputs command signals to the first electric motor and a second controller (50B) that receives input signals and outputs command signals to the second electric motor. The robotic ankle may comprise a first regenerative power stage (56A) to the first electric motor and a second regenerative power stage (56B) to the second electric motor and the first electric motor may be controlled by the first controller (50A) to operate in a regeneration mode and the second electric motor may be controlled by the second controller (50B) to operate in a regeneration mode. The robotic ankle may comprise a first electric storage device (55A) connected to the first electric motor and a second electric storage device (55B) connected to the second electric motor. The robotic ankle may comprise a first position sensor (51 A) configured to sense a position of the first piston and to provide an input signal to the first controller (50A), and a second position sensor (51B) configured to sense a position of the second piston and to provide an input signal to the second controller (50B).

[0009] The first housing (34A) may be connected to the lower leg member and the first actuating rod (38 A) may be connected to the foot member. The second housing (34B) may be connected to the lower leg member and the second actuating rod (38B) may be connected to the foot member. The first actuating rod (138) may be connected to the lower leg member and the first housing (134) may be connected to the foot member.

[0010] The robotic ankle may comprise a first fluid reservoir (41, 41A) connected to the first hydraulic pump and the first hydraulic piston assembly, and the first hydraulic pump, the first hydraulic piston assembly and the first reservoir may be connected in a substantially closed hydraulic system. The first fluid reservoir (41) may be connected to the second hydraulic pump and the second hydraulic piston assembly, and the second hydraulic pump, the second hydraulic piston assembly and the first fluid reservoir may connected in a substantially closed hydraulic system. The robotic ankle may comprise a second fluid reservoir (41B) connected to the second hydraulic pump and the second hydraulic piston assembly, and the second hydraulic pump, the second hydraulic piston assembly and the second reservoir may be connected in a substantially closed hydraulic system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a representative perspective view of a first embodiment of an improved humanoid robot.

[0012] FIG. 2 is a front view of the humanoid robot shown in FIG. 1.

[0013] FIG. 3 is an enlarged right view of the robotic ankle shown in FIG. 2.

[0014] FIG. 4 is a view of the robotic ankle shown in FIG. 3 pitched counter-clockwise 45 degrees about its pitch axis.

[0015] FIG. 5 is a view of the robotic ankle shown in FIG. 3 pitched clockwise 45 degrees about its pitch axis.

[0016] FIG. 6 is an enlarged front view of the robotic ankle shown in FIG. 2.

[0017] FIG. 7 is a view of the robotic ankle shown in FIG. 6 rolled clockwise 45 degrees about its roll axis.

[0018] FIG. 8 is a view of the robotic ankle shown in FIG. 6 rolled counter-clockwise 45 degrees about its roll axis. [0019] FIG. 9 is a schematic system diagram of the electro-hydraulic actuator system shown in FIG. 2.

[0020] FIG. 10 is a schematic system diagram of an alternative embodiment of the electro- hydraulic actuator system shown in FIG. 2.

[0021] FIG. 11 is a schematic diagram of each of the electro-hydraulic actuator units shown in FIG. 9.

[0022] FIG. 12 is a view of an alternative embodiment of the robotic ankle shown in FIG. 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] 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., crosshatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description. 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.

[0024] Referring to the drawings, and more particularly to FIGS. 1 and 2, an improved robotic ankle is provided, of which a first embodiment is generally indicated at 16. In this embodiment, robotic ankle 16 is part of humanoid robot 15 and generally comprises lower leg member 18 connected at ball joint 20 to foot member 19. Ball joint 20 generally comprises ball 21 at the end of lower leg 18 disposed in correspondingly-sized socket 22 in the heel portion of foot 19. Joint 20 allows foot portion 19 to be rotated in at least two degrees of freedom about center 23 of joint 20. Thus, the connection between lower leg 18 and foot 19 provides for rotation of foot 19 about two axes of rotation 24 and 25 that intersect at right angles at ankle center 20. FIG. 1 provides a frame of reference about joint center 23 that includes pitch axis 24 and roll axis 25 orientated perpendicular to pitch axis 24.

[0025] Ankle actuator system 17 actuates foot 19 relative to lower leg 18 at joint 20. Ankle actuator system 17 includes two side-by-side electro hydrostatic actuators 30A and 30B. Referring now to FIG. 9, in a first embodiment actuator 30A of actuator system 17 is schematically indicated as including variable speed bidirectional electric servomotor 31 A, bidirectional or reversible pump 32A driven by motor 31 A, and double-acting hydraulic piston assembly 33A. Actuator 30B of actuator system 17 is schematically indicated as including variable speed bidirectional electric servomotor 3 IB, bidirectional or reversible pump 32B driven by motor 3 IB, and double-acting hydraulic piston assembly 33B. Controller 50 supplies a signal to regenerative power stage 56A, which in turn supplies a current of the appropriate magnitude and polarity to motor 31 A, and controller 50 supplies a signal to regenerative power stage 56B, which in turn supplies a current of the appropriate magnitude and polarity to motor 3 IB.

[0026] FIG. 11 is a schematic view for both electro-hydraulic actuators 30A and 30B. As described above and with reference to FIG. 11, each actuator 30A, 30B includes, respectively, variable speed bidirectional electric servomotor 31A, 31B, bidirectional or reversible pump 32A, 32B driven by motor 31A, 31B, and double-acting hydraulic piston assembly 33A, 33B. In this embodiment, each motor 31A, 31B is a brushless D.C. variable- speed servo-motor that is supplied with a current. Each motors 31 A, 3 IB has an inner rotor with permanent magnets and a fixed non-rotating stator with coil windings. When current is appropriately applied through the coils of the stator, a magnetic field is induced. The magnetic field interaction between the stator and rotor generates torque which may rotate output shaft 40A, 40B, respectively. When the supplied current is of one polarity, the motor will rotate in one direction. When the supplied current supplied is of the opposite polarity, the motor will rotate in the opposite direction. Accordingly, each motors 31 A, 3 IB will selectively apply a torque on its respective output shaft 40A, 40B in one direction about axis x-x at varying speeds and will apply a torque on its respective output shaft 40 A, 40B in the opposite direction about axis x-x at varying speeds. Other motors may be used as alternatives. For example, a variable speed stepper motor, brush motor or induction motor may be used.

[0027] In this embodiment, each pumps 32A, 32B is a fixed displacement bi-directional internal two-port gear pump. The pumping elements, namely gears, are capable of rotating in either direction, thereby allowing hydraulic fluid to flow in either direction. This allows for oil to be added into and out of the system as the system controller closes the control loop of position or pressure. The shaft of at least one gear of each pump 32A, 32B is connected to output shaft 40 A, 40B of motor 31 A, 3 IB, respectively, with the other pump gear following. The direction of flow of each pump 32A, 32B depends on the direction of rotation of motor 31A, 31B and output shaft 40A, 40B, respectively. In addition, the speed and output of each pump 32A, 32B is variable with variations in the speed of motor 31A, 31B, respectively. Other bi-directional pumps may be used as alternatives. For example, a variable displacement pump may be used.

[0028] In this embodiment, each hydraulic piston assembly 33A, 33B includes, respectively, piston 37A, 37B slidably disposed within cylindrical housing 34A, 34B such that piston 37A, 37B may be driven in both directions relative to housing 34A, 34B. Each piston 37A, 37B sealingly separates left chamber 35A, 35B from right chamber 36A, 36B, respectively. As shown in FIG. 11, one side or port 42 of each pump 32A, 32B communicates with left chamber 35A, 35B via fluid line 44, respectively, and the opposite side or port 43 of each pump 32A, 32B communicates with right chamber 36A, 36B via fluid line 45, respectively. Each piston 37A, 37B is connected to actuating rod 38A, 38B, respectively. Each bidirectional motor 31A, 31B turns bidirectional pump 32A, 32B and bidirectional pump 32A, 32B is hydraulically connected to equal area piston actuator 33A, 33B, respectively. Each pump 32A, 32B and piston actuator 33A, 33B is a hydrostatic transmission, so as pump 32A, 32B spins in a first direction, piston 37A, 37B and rod 38A, 38B move in a first direction and as pump 32A, 32B spins in the other direction, piston 37A, 37B and rod 38A, 38B move in the other direction, respectively. Thus, each piston 37A, 37B will extend or move rod 38 A, 38B to the left when bidirectional motor 31 A, 3 IB is rotated in a first direction, thereby rotating bidirectional pump 32A, 32B in a first direction and drawing fluid through port 42 from line 44 and chamber 35A, 35B, respectively. Each piston 37A, 37B will retract rod 38 A, 38B or move to the right when bidirectional motor 31 A, 3 IB is rotated in the other direction, rotating bidirectional pump 32A, 32B in the other direction and drawing fluid through port 43 from line 45 and chamber 36A, 36B, respectively.

[0029] In this embodiment, oil reservoir 41 compensates for thermal oil expansion and contraction within the systems and is controlled by check valves 46A and 46B. Connection ports 48A and 48B are used to fill the system with oil. Line 49 provides a pump casing leakage relief conduit to reservoir 41. The electrohydraulic actuator is a closed hydraulic system in that fluid is not supplied to the system from an external source in operation. Nor is fluid permitted to drain to an external sump in operation. Rather, reservoir 41 is either discharged or recharged, as appropriate, to accommodate differential fluid volumes. Motors 31 A and 3 IB are required to provide torque and consume power when motions work against gravity.

[0030] Controller 50 receives feedback from sensors in the system and controls motors 31A and 31B accordingly. Controller 50 controls the current to motors 31A and 31B at the appropriate magnitude and direction. With reference to FIG. 9, motor controller 50 supplies current command signals 58A and 58B to power stages 56A and 56B, respectively, which in turn supply current of the appropriate magnitude and polarity to motors 31 A and 3 IB, respectively, with such commands based in part on angular position feedback from respective resolvers 61A and 61B. Thus, controller 50 provides commands to vary the speed and direction of motors 31A and 31B, respectively. The positions of rods 38A and 38B are monitored via position transducers 51A and 5 IB, respectively, and the position signals are then fed back to motor controller 50. In addition or alternatively, the pressure in lines 44 and 45 to chambers 35A, 35B and 36A, 36B may be monitored with pressure transducers, respectively, and the pressure signals may be fed back to motor controller 50. Variable speed bidirectional motors 31A and 31B and pumps 32A and 32B control the speed and force of pistons 37A, 37B, and in turn rods 38A and 38B, respectively, by changing the flow and pressure acting on piston 37A and 37B. This is accomplished by looking at the feedback of position transducers 51 A and 5 IB and/or pressure transducers and then closing the control loop by adjusting the speed and direction of motors 31A and 31B accordingly. While in this embodiment position sensors 51 A and 5 IB are magnetostrictive linear position sensors, other position sensor may be used. For example, an LVDT position sensor may be used as an alternative.

[0031] As shown, the top end of each cylinder housing 34A, 34B of each actuator unit 30A and 30B is pivotally connected at pivot connections 26A and 26B, respectively, to lower leg portion 18. As shown in FIG. 3, in the non-pitched and non-rolled position, such pivot connections 26A and 26B are at the same height on lower leg portion 18 and are offset up lower leg 18 from ankle center 23 relative to vertical axis z-z by distance 52.

[0032] The outer end of each actuating rod 38 A, 38B of each actuator unit 30A and 30B includes a ball end and is rotationally connected at ball joints 28 A and 28B, respectively, to foot portion 19. As shown in FIG. 3, in the non-pitched and non-rolled position, ball joint 28 A is offset on foot 19 horizontally from roll axis 25 on a first side of roll axis 25 by distance 53A. As shown in FIG. 3, in the non-pitched and non-rolled position, ball joint 28B is offset on foot 19 horizontally from roll axis 25 on a second side of roll axis 25 by distance 53B. In this embodiment, distance 53A and 53B are the same. However, it is contemplated that distances 52, 53A and 53B could be varied depending on the desired dynamics. Accordingly, connections 26A, 26B, 28A and 28B are located relative to ball joint 20 and joint center 23 so that actuators 30A and 30B may be controlled to rotate foot portion 19 up or down about pitch axis 24 relative to lower leg portion 18. Connections 26 A, 26B, 28A and 28B are also located relative to ball joint 20 andjoint center 23 so that actuators 30A and 30B may be controlled to rotate foot portion 19 left or right about roll axis 25 relative to lower leg portion 18. Thus, in this embodiment ankle actuator system 17 provides +/-45 degrees of angular movement, both in pitch and roll, between leg portion 18 and foot portion 19 of ankle joint 16.

[0033] With reference to FIG. 9, when one or both of actuators 30A and 30B need to absorb gravitational forces and impact forces, each of motors 31A and 3 IB is configured to operate as an electric generator that converts torque generated from such forces on the system into electricity that is stored in battery or capacitor bank 55. Thus, actuator system 17 includes regenerative energy functionality. As shown, motor controller 50 supplies current command 58A to regenerative power stage 56A, which in turn supplies the current at an appropriate magnitude and polarity to motor 31A to power electro-hydraulic actuator 30A. The position of piston 37A or actuator rod 38A of actuator 30A is monitored via linear feedback position sensor 51 A, and such position signals are then fed back to motor controller 50. Motor controller 50 also supplies current command 58B to regenerative power stage 56B, which in turn supplies the current at an appropriate magnitude and polarity to motor 3 IB to power electro-hydraulic actuator 30B. The position of piston 37B or actuator rod 38B of hydraulic actuator 30B is monitored via linear feedback positional sensor 5 IB, and such position signals are then fed back to motor controller 50. In this manner, system 17 controls the motion of humanoid robotic ankle joint 16 during the active or“power stroke of the joint.” A significant percentage of the total motion is resisting the effects of a gravity load. During the “regenerative stroke of the joint,” the effects of gravity will generate a force on one or both of pistons 37A and 37B of hydraulic actuators 30A and 33B, which in turn produces pressure on respective pumps 32A and 32B, which in turn produces a torque on respective shafts 40A and 40B and to respective servomotors 31A and 31B. Under these conditions and in the regenerative mode, electric motor 31A and electric motor 3 IB are each configured to act as an electric generator. Regenerative power stages 56A and 56B and motor controller 50 detect the armature current 59A and 59B generated by motor 31A and 31B, respectively, in this capacity and transfers such current of the appropriate magnitude and polarity of motor 31A and/or motor 3 IB into battery 55. Such stored electrical energy may then be used to power one or both of motors 31 A and 3 IB and control the movement of electro-hydraulic actuator 17 in the active or“power stroke of the joint” mode. Since a humanoid robot may have limited battery power capacity, capturing regenerative power is beneficial. This regenerative power circuit takes advantage of a mode in which motor 31A and/or motor 3 IB is controlled to operate as a generator in a regeneration mode.

[0034] In the embodiment 17 shown in FIG. 9, a single common motor controller 50 is shown controlling both actuator units 30A and 30B, a common battery or capacitor 55 is shown for storing regenerative power from both motors 31A and 31B, and a common reservoir 41 is shown for both hydraulic piston assemblies 33 A and 33B. However, is contemplated that each actuator unit 30A and 30B may have its own motor controller, each actuator unit 30A and 30B may have its own battery or capacitor, and/or each actuator unit 30A and 30B may have its own reservoir. For example, FIG. 10 shows an alternative distributed embodiment 117 in which each actuator unit 30A and 30B has its own motor controller 50A and 50B, respectively, each actuator unit 30A and 30B has its own regeneratively chargeable battery or capacitor 55 A and 55B, respectively, and each actuator unit 30A and 30B has its own hydraulic reservoir 41A and 41B, respectively. In this embodiment, a master signal is supplied to each of two distributed motor controllers 50A and 50B. Each motor controller 50A and 50B supplies a signal to respective power stage 56A and 56B which in turn supplies the current of the appropriate magnitude and polarity to respective motors 31A and 31B. The position of each rod 38A and 38B is monitored via position sensors 51 A and 5 IB, respectively, and the position signals are then fed back to their associated motor controllers 50A and 50B, respectively. Thus, in this manner, the system may control the stroke of each actuator unit 30A and 30B entirely independently.

[0035] FIGS. 1-8 show an embodiment 16 in which housings 34A and 34B of actuator units 30A and 30B are connected to lower leg 18 and actuation rods 38A and 38B of actuator units 30A and 30B are connected to foot 19. However, it is contemplated that this arranged may be reversed such that for one or both of the housings of actuator units 30A and 30B is connected to foot 19 and one or both of the actuating rods of actuator units 30A and 30B is connected to lower leg 18. FIG. 12 shows an alternative embodiment 116 in which housing 134 of actuator unit 130 is connected to foot 19 and actuating rod 138 of actuator unit 130 is connected to lower leg 18. As shown, in this embodiment the bottom end of cylinder housing 134 of actuator unit 130 includes a ball end and is rotationally connected at ball joint 128 to foot portion 19. The outer end of actuating rod 138 of actuator unit 130 is pivotally connected at pivot connection 126 to lower leg portion 18.

[0036] While the presently preferred form of an improved robotic ankle has been shown and described, and several modifications thereof discussed, persons skilled in this art will readily appreciate that various additional changes and modifications may be made without departing from the scope of the invention, as defined and differentiated by the claims.

Claims

CLAIMS What is claimed is:

1. A robotic ankle comprising:

a lower leg member;

a foot member;

an ankle joint between said lower leg member and said foot member;

said ankle joint having an ankle center;

said foot member configured to rotate about a pitch axis extending through said ankle center and to rotate about a roll axis extending through said ankle center;

a first electric motor adapted to be supplied with a current and to operatively provide a torque on a first output shaft;

a first hydraulic pump driven by said first output shaft of said first electric motor; a first hydraulic piston assembly hydraulically connected to said first hydraulic pump and comprising a first housing having a first chamber and a second chamber, and a first piston separating said first and second chambers of said first housing;

a first actuating rod connected to said first piston and configured to move linearly with said first piston relative to said first housing;

one of said first housing or said first actuating rod connected to said lower leg member and the other of said first housing or said first actuating rod connected to said foot member;

said first hydraulic piston assembly configured to actuate said foot member relative to said lower leg member within a range of motion about said pitch axis;

a second electric motor adapted to be supplied with a current and to operatively provide a torque on a second output shaft;

a second hydraulic pump driven by said second output shaft of said second electric motor;

a second hydraulic piston assembly hydraulically connected to said second hydraulic pump and comprising a second housing having a first chamber and a second chamber, and a second piston separating said first and second chambers of said second housing;

a second actuating rod connected to said second piston and configured to move linearly with said second piston relative to said second housing; one of said second housing or said second actuating rod connected to said lower leg member and the other of said second housing or said second actuating rod connected to said foot member;

said second hydraulic piston assembly configured to actuate said foot member relative to said lower leg member within a range of motion about said pitch axis;

said first hydraulic piston assembly and said second hydraulic piston assembly configured to actuate said foot member relative to said lower leg member within a range of motion about said roll axis;

whereby rotation of said foot member relative to said lower leg member about said pitch axis and about said roll axis is controllable by said first electric motor and said second electric motor.

2. The robotic ankle set forth in claim 1, wherein said first electric motor is a variable speed bidirectional electric motor adapted to operatively provide a torque on said first output shaft at varying speeds and by direction, said second electric motor is a variable speed bidirectional electric motor adapted to operatively provide a torque on said second output shaft at varying speeds and by direction, said first hydraulic pump is a reversible variable speed hydraulic pump, said second hydraulic pump is a reversible variable speed hydraulic pump, and whereby rotation of said foot member relative to said lower leg member about said pitch axis and about said roll axis is controllable by adjusting said speed and/or direction of said first variable speed bidirectional electric motor and said speed and/or direction of said second variable speed bidirectional electric motor.

3. The robotic ankle set forth in claim 1, wherein said first electric motor comprises a brushless DC servo-motor and said second electric motor comprises a brushless DC servo motor.

4. The robotic ankle set forth in claim 1, wherein said first hydraulic pump is selected from a group consisting of a fixed displacement pump, a variable displacement pump, a two- port pump, and a three-port pump.

5. The robotic ankle set forth in claim 1, wherein said first piston comprises a first surface area exposed to said first chamber of said first housing and a second surface area exposed to said second chamber of said first housing, and wherein said second piston comprises a first surface area exposed to said first chamber of said second housing and a second surface area exposed to said second chamber of said second housing.

6. The robotic ankle set forth in claim 5, wherein said first surface area is substantially equal to said second surface area.

7. The robotic ankle set forth in claim 1, wherein said first housing comprises a cylinder having a first end wall, wherein said piston is disposed in said cylinder for sealed sliding movement therealong, and wherein said first actuator rod is connected to said piston for movement therewith and comprises a portion sealingly penetrating said first end wall.

8. The robotic ankle set forth in claim 1, comprising a controller that receives input signals and outputs command signals to said first electric motor and/or said second electric motor to control rotation of said foot member relative to said lower leg member about said pitch axis and about said roll axis.

9. The robotic ankle set forth in claim 8, comprising a regenerative power stage to said first electric motor and/or said second electric motor and wherein said first electric motor and/or said second electric motor may be controlled by said controller to operate in a regeneration mode.

10. The robotic ankle set forth in claim 9, comprising an electric storage device connected to said first electric motor and/or said second electric motor.

11. The robotic ankle set forth in claim 8, wherein said controller outputs command signals to said first electric motor and said second electric motor to control rotation of said foot member relative to said lower leg member about said pitch axis and about said roll axis.

12. The robotic ankle set forth in claim 11, comprising a first regenerative power stage to said first electric motor and a second regenerative power stage to said second electric motor and wherein said first electric motor and said second electric motor may be controlled by said controller to operate in a regeneration mode.

13. The robotic ankle set forth in claim 12, comprising an electric storage device connected to said first electric motor and said second electric motor.

14. The robotic ankle set forth in claim 11, comprising a first position sensor configured to sense a position of said first piston and to provide an input signal to said controller, and a second position sensor configured to sense a position of said second piston and to provide an input signal to said controller.

15. The robotic ankle set forth in claim 1, comprising a first controller that receives input signals and outputs command signals to said first electric motor and a second controller that receives input signals and outputs command signals to said second electric motor.

16. The robotic ankle set forth in claim 15, comprising a first regenerative power stage to said first electric motor and a second regenerative power stage to said second electric motor and wherein said first electric motor may be controlled by said first controller to operate in a regeneration mode and said second electric motor may be controlled by said second controller to operate in a regeneration mode.

17. The robotic ankle set forth in claim 16, comprising a first electric storage device connected to said first electric motor and a second electric storage device connected to said second electric motor.

18. The robotic ankle set forth in claim 15, comprising a first position sensor configured to sense a position of said first piston and to provide an input signal to said first controller, and a second position sensor configured to sense a position of said second piston and to provide an input signal to said second controller.

19. The robotic ankle set forth in claim 1, wherein said first housing is connected to said lower leg member and said first actuating rod is connected to said foot member.

20. The robotic ankle set forth in claim 13, wherein said second housing is connected to said lower leg member and said second actuating rod is connected to said foot member.

21. The robotic ankle set forth in claim 1, wherein said first actuating rod is connected to said lower leg member and said first housing is connected to said foot member.

22. The robotic ankle set forth in claim 1, comprising a first fluid reservoir connected to said first hydraulic pump and said first hydraulic piston assembly and wherein said first hydraulic pump, said first hydraulic piston assembly and said first reservoir are connected in a substantially closed hydraulic system.

23. The robotic ankle set forth in claim 22, wherein said first fluid reservoir is connected to said second hydraulic pump and said second hydraulic piston assembly and wherein said second hydraulic pump, said second hydraulic piston assembly and said first fluid reservoir are connected in a substantially closed hydraulic system.

24. The robotic ankle set forth in claim 22, comprising a second fluid reservoir connected to said second hydraulic pump and said second hydraulic piston assembly and wherein said second hydraulic pump, said second hydraulic piston assembly and said second reservoir are connected in a substantially closed hydraulic system.