A QUADRUPED LEGGED ROBOT DRIVEN BY LINEAR ACTUATORS

Field of the Invention

The present invention relates to the field of legged robots. More particularly, the invention relates to a quadruped legged robot driven by pneumatic linear actuators.

Background of the Invention

One of the main advantages of an articulated walking robot is in its ability to traverse very rough, uneven, and cluttered terrains. This feature is a key property in various applications. For example, maintenance of hazardous structures such as nuclear reactors, planetary exploration, and transportation in places where paved roads does not exist. All these applications require a reliable and mobile machine which has the ability to adjust its motion pattern with respect to changes in the environment. The present invention aims to provide an autonomous four-legged (quadruped) walking machine capable of traversing various classes of rough terrains. The four-legged walking machine of the present invention is inspired by many species of wild animals capable of such motion; examples are mountain goats, tigers, cats, dogs, horses, monkeys, mules... etc.

Prof. Marc Raibert developed the first self-balancing hopping robots at the MIT Leg Lab. Raibert 's quadruped robot [Raibert et al., "Running on Four Legs As Though They Were One", IEEE J. of robotics and automation, Vol. RA-2, No. 2, June 1986] was capable of running on four legs, trotting, pacing, bounding, by using simple control laws. In this work only

quadruped gaits that use the legs in pairs (trotting, pacing, bounding) were considered, which enabled to reduce the quadruped control to that of a virtual biped equivalent.

1

Raibert ' s pioneering work laid the foundations for many studies in the field of quadruped legged robots.

The insect-like walking robot described by Marc-Andre Lavoie et al . , ("Design of an insect-like walking robot by Peris", Society of Automotive Engineers, Inc. 2004) was designed to achieve straight line running on six legs having 12 degrees of freedom actuated by means of DC motors, and pneumatic and hydraulic cylinders actuators. In this design the legs of the robot were implemented by a pneumatic cylinder and a torsion spring was employed in the shoulder part for damping vibrations in the angular movement of the leg.

The "Scout" quadruped robot design demonstrated walking, turning, climbing and running capabilities, with one degree of freedom per leg. In the Scout design RC-Servo motors were used as rotary hip actuators for actuating four stiff legs (Scout I), and in a later design passive compliant prismatic legs (Scout H)[M. Buehler et al., "SCOUT: A simple quadruped that walks, climbs, and runs", Proc. Of the 1998 IEEE Int. Conf . on Robotics & Automation, May 1998] [D. Papadopoulos and M. Buehler, "Stable Running in a Quadruped Robot with Compliant Legs", Proc. Of the 2000 IEEE Int. Conf. on Robotics & Automation, April 2000] .

A robot apparatus that is able to perform jumping is described in US Patent No. 6,484,068. The robot apparatus in this patent aims to simulate the shape of an animal (pet robot) , and accordingly it is constructed from leg structures comprising two parts connected by a connecting member forming

a knee. The two part legs are rotatably actuated by means of a servo motor driving a rotary member linked to the connecting member by means of two connecting rods forming a four-point link mechanism. A coil spring mounted on the leg structure is employed to permit the robot apparatus to perform jumping.

A four legged robot designed for climbing walls for assisting in fire fighting in buildings is described in Chinese publication CN1569287.

Heretofore legged robot designs did not provide suitable solutions allowing to simplify the construction and control, of legged robots, and for providing relatively inexpensive designs suitable for industrial, agriculture, military, and load transformation applications.

It is therefore an object of the present invention to provide a simplified legged robot employing linear actuators.

It is another object of the present invention to provide a simplified legged robot actuated by linear actuators which is suitable for transferring loads over long distances to predefined destinations.

It is a further object of the present invention to provide a simplified legged robot actuated by linear actuators having efficient energy consumption and capable of traveling in rough terrains autonomously.

It is yet another object of the present invention to provide a simplified and reliable legged robot, which is relatively inexpensive and low weight (with respect to payload) , which

- A - is easy and simple to assemble and disassemble, having uniform symmetric design and which utilizes actuators as structural components.

Other objects and advantages of the invention will become apparent as the description proceeds.

Summary of the Invention

The present invention provides a simplified legged robot actuated by linear actuators which is suitable for performing various tasks, such as, inter alia, transferring loads over long distances to predefined destinations and traveling through rough terrains autonomously.

The inventor hereof developed a legged robot which legs are actuated by means of linear actuators capable of applying leg movement within three allowable degrees of freedom. More particularly, each of the robot's legs is actuated by means of three linear actuators each of which is comprised of an elongated hollow body having an opening at one of its ends from which a movable shaft may be contracted thereinto or extracted therefrom along a longitudinal axis thereof, wherein the robot ' s leg is constructed from a first linear actuator attached to the body of the robot by means of a joint capable of providing two degrees of freedom to said leg, and wherein the second and third linear actuators are attached to said leg at points situated more or less at the same level along its length (i.e., located more or less with the same distances from the ends of the actuator) in selected angular positions with respect thereto, such that it may be moved within the two degrees of freedom provided by the

joint. This configuration may be employed for altering the length of each leg by prolonging or shortening its first linear actuators, and for rotating it about two rotational axes relative to the body of the robot by means of its second and third actuators.

Preferably, the body of the robot is made from a substantially flat board or frame and the second and third linear actuators are configured to allow rotating each leg about longitudinal and lateral axes relative to said body. Preferably, the second and third linear actuators are attached to the robot's leg such that an angle in the range of 20° to 70°, preferably 30° to 60°, most preferably of more or less 45°, is obtained between said leg and said second actuator, and between said leg and said third actuator, when said robot is in an initial state in which a 90° angle is obtained between each leg and the lateral axis, and between each leg and the longitudinal axis, of the robot's body. It was realized that this configuration of the legged robot of the invention substantially improves its efficiency, reduces the energy consumption due to the reduced actuator movements needed during locomotion.

The linear actuators may be implemented from types of electric, hydraulic or pneumatic linear actuators, or combinations thereof. In a preferred embodiment of the invention all of the linear actuators of the robot are implemented by type(s) pneumatic actuator (s). It was found that this configuration (uniform symmetric design using actuators as structural components) substantially improve the robot's reliability, reduces its weight (with respect to payload) and its manufacture costs, and simplifies the robot's construction, assembly and disassembly.

The robot is preferably a quadruped robot equipped with power supply (s) and management control means for allowing it to move autonomously. A quasi-static locomotion scheme is preferably implemented by the control means, wherein at any given time at least three of the robot's legs are pressing the ground against gravity, while lifting a fourth leg to a new foothold position. In a preferred embodiment of the invention employing pneumatic actuators a system for supplying the actuators pressurized gas (e.g., air) streams is attached to the body of the robot, comprising: an air compressor; a combustion engine having a fuel tank, for driving the air compressor; a gas tank capable of being filled with pressurized gas supplied from the air compressor; and valve manifold capable of directing streams of pressurized gas to the actuators.

Control means (e.g., computer, controller) is preferably used for controlling the valve manifold such the pressurized air streams are directed to specific actuator (s) for affecting leg(s) movement (s). The pneumatic actuators typically comprise a plunger, and a first chamber and a second chamber defined by the position of said plunger inside the actuator hollow interior, wherein each of said chambers is accessible via a port provided in said actuators. An actuator operating mechanism may be used for operating the pneumatic actuators by means of two normally-closed valves each of which connected to one of the chamber ports of the actuator, and a controllable three-state valve (e.g., 5/3 valve) capable of directing the streams of pressurized gas to an inlet port of one of the normally-closed valves, wherein the state of said normally-closed valves is altered by means of a pneumatic input.

In one aspect the present invention is directed to a legged robot comprising at least four legs each of which attached to a body of said robot by means of a joint capable of providing two degrees of freedom, wherein each leg comprises: a first linear actuator capable of shortening or elongating the length of said leg; a second linear actuator capable of rotating said leg about a longitudinal axis of said body; and a third linear actuator capable of rotating said leg about a lateral axis of said body, wherein each leg is substantially constructed from said first linear actuator, and wherein said second and third linear actuators are connected to said leg at points situated more or less at the same level along its length .

The first, second and third linear actuators may be implemented by a type of electric, hydraulic or pneumatic actuator .

Advantageously, the legs of the robot further comprise linear guiding means .

Optionally, the moving shafts of the second and third linear actuators are connected to in each leg by means of pivots. Alternatively, the moving shafts of the second and third linear actuators are connected to the legs by means of joints capable of providing two degrees of freedom. Preferably, the joints used are selected from the group consisting of: spherical joints, spherical bearing joints, universal joints, or an assembly of two pivot joints interconnected in a series arrangement.

Preferably, at least one of the first, second or third, linear actuators is a pneumatic actuator comprising two pneumatic ports, and wherein said robot further comprises a gas tank for storing pressurized gas, pneumatic valve means connected to said gas tank and capable of directing streams of said pressurized gas to an actuator control mechanism capable of supplying said gas streams to said ports.

The robot may further comprise sensing means capable of producing indications responsive to the length of the legs.

Control means are preferably used for receiving indications produced by the sensing means, and for controlling the operation of the valve means and actuator control mechanism.

The actuator control mechanism may comprise two normally- closed valves each of which connected to a pneumatic port of a pneumatic actuator, wherein the state of said normally- closed valves is capable of being altered by means of a pneumatic input. The actuator control mechanism preferably further comprises a controllable three-state valve capable of directing the streams of pressurized gas to an inlet port of one of the normally-closed valves.

The angle between the legs and the second linear actuators, and between the legs and the third linear actuators, in an initial state, in which there are more or less straight angles between said legs and said body, may be in the range of 20° to 70° .

The robot may further comprise an internal combustion engine and an air compressor capable of filling the gas tank with pressurized gas.

Preferably, specific gait patterns are employed such that at every instance three legs of the robot touches the ground. An inertial measurement unit may be used for adapting foothold positions to maintain robot stability. Additionally, obstacle detection sensors may be used for detecting possible obstacles along the robot's path.

In another aspect the present invention is directed to a robot leg having three degrees of freedom comprising a first linear actuator capable of elongating or shortening the length of said leg, a joint connected to one end of a body section of said first linear actuator and capable of providing two degrees of freedom, and a second and third linear actuators connected to said leg at points situated more or less at the same level along its length, wherein said leg is substantially constructed from said first linear actuator. The robot leg may further comprise linear guide means, foot element connected to a moving shaft of the first linear actuator, and/or sensing means capable of producing indications responsive to the length of the leg.

Brief Description of the Drawings

The present invention is illustrated by way of example in the accompanying drawings, in which similar references consistently indicate similar elements and in which:

Fig. 1 schematically illustrates the structure of the quadruped robot of the invention;

Fig. 2 is a block diagram showing the energy flow in a preferred embodiment of the invention;

Fig. 3 exemplifies one preferred embodiment of the quadruped robot of the invention wherein the joints are implemented by spherical joints;

Figs. 4A to 4F illustrate a preferred embodiment of the invention wherein the joints are implemented by spherical bearing joints, wherein Fig. 4A illustrates a perspective view of the quadruped robot, Fig. 4B illustrates a suitable type of rod-end spherical bearing, Fig. 4C illustrates the connectivity of the lateral motion actuators, Fig. 4D illustrates the structure of the legs of the robot, Fig. 4E illustrates the linear guide used in each leg, and Fig. 4F illustrates the structure of the attachment assemblies used in the robot's legs;

Fig. 5 is a block diagram schematically illustrating a preferred pneumatic control for the linear actuators; Fig. 6 is a flowchart of a preferred control system for the four-legged robot of the invention; and Figs. 7A to 7C illustrates a preferred embodiment employing universal joints in the robot shoulder, wherein Fig. 7A is a perspective view of the robot, Fig. 7B shows a perspective view of the leg actuator with a universal joint, and Fig. 7C is a perspective view of a universal joint.

It should be noted that the embodiments exemplified in the Figs, are not intended to be in scale.

Detailed Description of Preferred Embodiments

Developing a four-legged walking machine is challenging in many aspects. One may categorize these challenges into three categories :

i) The mechanical design of the robot.

In the present invention each leg has three DOFs (degrees of freedom) - two rotational about shoulder/hip joint and the third is ^' leg elongation/retraction. All three DOFs are actuated by linear actuators, and most preferably pneumatic actuators, which were found to be advantageous. It was found that by constructing the robot's legs from such pneumatic actuators precludes the need for stabilizing and energy storing springs in the robot's legs.

ii) The robot's motion planning.

Given the robot's high number of DOFs, conventional robotics path planning algorithms are often too complex, in terms of very high computational complexity. Thus in the present invention a quasi-static locomotion planning scheme was employed. In quasi-static locomotion the robot time scale may be slowed down with no effect on the robot's motion. Hence the inertia forces are kept low with respect to contact forces with the environment and therefore almost do not affect the robot's motion. Specifically, quasi-static locomotion scheme permits gait patterns which maintain the robot in static equilibrium during every instance of its' motion .

iii) The control of the robot.

This challenge is actually related to the motion planning problem since the control strategy should assure that the robot actually follow the path designed by the motion planner. For this purpose a new control algorithm was

developed for assuring the stability of the four-legged walking machine of the invention.

Fig. 1 schematically illustrates a general structure of a preferred embodiment of the quadruped robot 10 of the invention. In the side view shown in Fig. 1 only two legs 15 of the quadruped robot 10 are seen. The four leg structure (as of robots 20 and 30 shown in Figs. 3 and AK, respectively) of robot 10 permits stable locomotion on general terrains, which allows robot 10 to stably support itself during motion by planning quasi-static locomotion schemes, wherein at any given time three of the robot's legs 15 are pressing the ground against gravity, while lifting a fourth leg to a new foothold position.

Robot 10 comprises two pairs of legs, 15r and 15f, wherein said pairs of legs are attached to opposing sides of a rectangular body 10a forming the body of robot 10. Each of the legs 15 is constructed from a linear actuator 161, preferably a pneumatic actuator. The advantages, inter alia, of pneumatic actuators are mainly in their physical strength, reliability, agility, control simplicity, and that they are simple to integrate, efficient and simple in terms of mechanical construction. In addition, pneumatic cylinders provide natural compliance at the joints, which is useful for stabilizing the mechanism. The body 10a of robot 10 is used as a platform for mounting various power source (s), management and control means such as air compressor 11, controllable valve manifold 12, controller 13, power source 14, fuel tank 9, and air tank 18, and for carrying payloads. In preferred embodiments of the invention air tank 18 is attached to the bottom face of body 10a.

The legs 15 are attached to the robot ' s body 10a by means of joints 17u suitable for allowing the legs 15 rotary motion in two DOFs. As shown in Fig. 3, each leg 15 possesses three actuated degrees of freedom, one is elongation and retraction (Ml) of the linear actuator 161 from which each leg 15 is constructed, and two rotational DOFs that allow rotation of the leg about a longitudinal axis (M2) and about a lateral axis (M3) of robot 20. This number of degrees of freedom allows each leg 15 to contact the environment at any point within its reachable work space.

Energy supply is a limiting factor that determines the robot's autonomous operational range. In order to obtain a reasonably large operational range, a scheme based on a small internal combustion engine driving an air compressor, is used in the preferred embodiment of the invention. The selection of fuel as an energy source yields higher power-per-weight ratio than battery operated electric motors. In fact, battery operated electric motors are often characterized by specific energy consumption of 1-200 watt-hours per kg, while fuel operated engines have a much higher energy consumptions of 30 to 1,100 watt-hours per kg.

Fig. 2 is a block diagram showing a preferred energy flow scheme for the quadruped robot 10 of the invention. In this energy flow scheme the air compressor 11 consists of an internal combustion engine 11a driving an air compressor unit lib. The fuel from fuel tank 9 is fed into internal combustion engine 11a, wherein the fuel' s chemical energy is converted into a mechanical energy. The combustion engine 11a drives the air compressor lib that compresses air into air tank 18. Air tank 18 is used for storing energy in the form of pressurized air. Responsive to control signals received

form controller 13, controllable valve manifold 12 directs pressurized air streams from the compressed air tank 18 through connecting tubes and control valves into the pneumatic cylinders 16 of the robot. Control signals generated by the controller 13 are used for opening and/or closing the control valves in order to drive the pneumatic cylinders 16 according to the desired motion paradigm.

Though in the preferred embodiment of the invention linear pneumatic actuators are employed, it should be understood that the quadruped robot of the invention may be also implemented with other types of linear actuators, such as for example electric or hydraulic actuators. In specific embodiment of the invention, for example, the robot legs may be constructed from a pneumatic actuator while the two rotary motion actuators may be implemented by electric or hydraulic linear actuators. Of course, if pneumatic actuators are not used the air compressor 11, air tank 18 and valve manifold 12, will not be required, and in case hydraulic actuators are employed other types of supporting and power supply and control means will be needed, the selection and operation of which is within the ability of one of ordinary skills in mechanical engineering.

Fig. 3 illustrates an exemplary embodiment of the invention showing a possible construction scheme of the body 20a and legs 15 of robot 20 (without the air compressor, air tank, fuel tank, and pneumatic/hydraulic/electronic control means shown in Fig. 1) . In this example body 20a is implemented by a flat board having elevated lateral sides .

As seen in Fig. 3, each leg 15 further comprises a longitudinal motion linear actuator 16r, used for rotating

leg 15 about joint 17u in the longitudinal direction (M2) , and a lateral motion linear actuator 16q, used for rotating leg 15 about joint 17u in the lateral direction (M3) . Longitudinal and lateral motion linear actuators, 16r and 16q, are attached to bottom face of body 20a of robot 20 by means of joints 17s. The moving shafts 16s of linear actuators, 16r and 16q, are attached by pivots 17i to an attachment element 15s which is tightly wrapped and affixed over linear actuator 161 of each leg 15. A rotatable foot element 19 is preferably attached by means of passive pivot (or alternatively by means of spherical or universal joints) 17b to the end of each moving shaft 16r of linear actuators 161 of leg 15.

In one specific embodiment the location of attachment elements 15s along the length of linear actuator 161, and the distances between joints 17s and joint 17u, of a leg 15, are preferably set such that an angle of about 45° is obtained between body 20a of robot 20 and the longitudinal and lateral motion actuators 16r and 16q, when the angle between linear actuator 161 and body 20a is about 90° and half of the retractable lengths of moving shafts 16s of actuators 16r and 16q is extracted. This construction is a compromise between two optimization criteria, one is to achieve maximum rotational torque, and the other is to achieve maximum rotational motion for the given ^' piston stroke. This leg construction was found beneficial for improving efficiency and for reducing linear movements of actuators 16r and 16q.

Longitudinal and lateral motion linear actuators 16r and 16q may be implemented by any suitable type of linear actuators capable of delivering the required motion powers, such as, but not limited to, electrical actuators (e.g., Phoenix

Mechano LBA5.7 ) , hydraulic actuators, and pneumatic actuators (e . g . , Baccara 1198405451 of Baccara Automation Control, Kibbutz Geva, Israel) . Preferably, longitudinal and lateral motion linear actuators 16r and 16q are implemented by pneumatic linear actuators, which were found preferable due to their advantageous characteristics discussed hereinabove.

In the exemplary embodiment shown in Fig. 3 spherical joints (e.g., Konlog 350140) were used for implementing joints 17u and 17s, used for connecting linear actuators 161 of legs 15, and longitudinal and lateral actuators 16r and 16q, to body 20a of robot 20, and the attachment of the longitudinal and lateral motion actuators 16r and 16q was implemented by means of pivots 17i. Figs. 4A to 4F illustrate a preferred embodiment of the invention wherein rod-end spherical bearing joints (37s shown in Fig. 4B) are employed in quadruped robot 30. In addition, the body 30a of robot 30 is made from a rectangular frame structure, preferably made from aluminum profiles, which may include one or more flat boards 30b for mounting the pneumatic/hydraulic/electric sources/controls (not shown), and/or other means or loads.

With reference to Fig. 4A, in robot 30 pairs of longitudinal motion actuators 36r are rotatably connected to the body 30a by means of attachment elements 37c, wherein to each actuator 36r there is attached a rod-end spherical bearing 37s rotatably attached to attachment element 37c by means of pivots 38p. Attachment element 37c comprises two parallel palates adapted to fixedly attach over a side of the frame structure of body 30a. As shown in Fig. 4B, rod-end spherical bearing 37s (e.g., Konlog End rod M16 350140) comprises a rotatable spherical member 37b having a through bore 37h suitable for receiving pivot 38p, which thus provides

actuators 36r two DOFs: i) rotations about pivot 38ρ; and ii) rotations about the longitudinal axis of actuators 36r. The moving shaft 36s of actuators 36r are attached to legs 35 of robot 30 by means rod-end spherical bearing joints 37s, wherein said spherical bearing joints 37s are rotatably attached by means of pivots 38p to attachment assemblies 31 fixedly attached to legs 35.

As shown in Fig. 4C lateral motion actuators 36q are attached to body 30a by means of an attachment element 38, wherein rod-end spherical bearing joint 37s attached to each actuator 36q are rotatably attached to attachment element 38 by means of pivots 38p. Attachment element 38 is preferably made in a shape of an isosceles right-angled triangle having two parallel plates 38r on its large base for fixedly attaching it over a side of the frame of body 30a. Each of the pivots 38p is attached between two parallel plates provided on the two other sides of attachment element 38. This attachment structure was found advantageous as it combines two attachment elements into a single element which allows relatively large rotational angles of the actuators about the rod end.

As best seen in Fig. 4D the leg 35 of robot 30 is made from a linear actuator 35a such that its length may be changed by retracting/extracting its moving shaft 35b. The foot element 39 attached to the end of moving shaft 35b comprises two linear guiding rods 32g of linear guide mechanism 32, said linear guiding rods 32g are passed along opposing sides of, and in parallel to, leg 35. Leg 35 is rotatably attached to body 30a of robot 30 by means of rod-end spherical bearing 37s which is attached to attachment element 35s by means of a pivot 38p. Attachment element 35s is preferably configured in

a shape of a straight angled triangle having attachment plates attached to its two sides, thereby allowing it to be firmly attached (e.g., by screws) over a corner of the frame of body 30a.

Fig. 4E shows a perspective view of linear guidance 32 comprising two parallel guiding rods 32g attached to foot element 39 of leg 35, and a "U"-shaped guide rail 32u having two rail bores 32a in its arms through which guiding rods 32g are movably passed (e.g., Baccara 129480050, containing two linear bearings) . As seen in Fig. 4D, guide rail 32u is attached to the end of the body of linear actuator 35a, preferably by means of screws, such that an end portion body of linear actuator 35a is received between the arms of "U"- shaped guide rail 32u and attached thereto (e.g., by screws).

Attachment assembly 31 of leg 35 also provides guide rails for guiding rods 32g in a form of two parallel bores 31b provided in two fastening elements thereof (32a and 32c in Fig. 4F) . The rails implemented by bores 31b and 32a are adapted to allow smooth passage of guiding rods 32g, thereby allowing them to move therethrough with minimal friction whenever moving shaft 35b of linear actuator 35 is retracted/extracted.

Fig. 4F shows an exploded perspective view of attachment assembly 31 comprising a two part fastening base consisting of a "U"-shaped element 32c and a "T"-shaped element 32a, and two attachment elements 32b and 32e. Fastening base of attachment assembly 31 is configured to fixedly attach to the body of linear actuator 35 such that the arms of "U"-shaped element 32c tightly hug actuator 35 and the "T"-shaped element 32a is attached over said arms by screws, thereby

forming a closure within which a portion of the actuator 35 is tightly held. The base of "ϋ"-shaped element 32c, and the leg of "T"-shaped element 32a, are made wide enough for providing rails (bores 31b) to be passed therethrough.

The attachment element 32b, configured to provide attachment for a longitudinal motion actuator 36r by means of pivot 38p and rod-end spherical bearing 37s, is attached to the outer side of the base of "U"-shaped element 32c. Attachment element 32e, configured to provide attachment for a lateral motion actuator 36r by means of pivot 38p and rod-end spherical bearing 37s, is attached to the outer side of an arm of "U"-shaped element 32c. The arms 32j used for holding pivot 38p in attachment element 32e are preferably formed such that an angle of more or less 45° is obtained between them and the base 32k of attachment element 32e. In this way, the opening provided between arms 32j of attachment element 32e is directed in the direction of the lateral motion actuators 36q such that the joint attached to the end of its moving shaft is received between said arms and can be easily rotated therebetween. This configuration was found advantageous since it allows maximum range of motion for all the joints.

Though linear actuator 35 may be implemented by a suitable type of electric or hydraulic actuator, pneumatic actuators were found to be preferable due to the advantages discussed hereinabove .

In a specific embodiment of the invention leg 35 is implemented by a type of pneumatic actuator capable of working with pressure ranges generally about 0.3-0.5 Mpa, but the robot may be designed for working with other suitable

pressure ranges. The length of pneumatic actuator 35a may generally be in the range of 200 to 600 mm, preferably about 520 mm. Longitudinal motion actuators 36r and lateral motion actuators 36q may be implemented by a type of pneumatic actuator having similar characteristics as actuator 35a. The lengths of longitudinal motion actuators 36r, and of lateral motion actuators 36q, may generally be in the range of 240 to 400 mm, preferably about 352 mm.

Attachment means (e.g., 35s, 32b, 37c), the attachment assemblies 31, and the different parts of linear guide 32, may be manufactured from any suitable plastic or metallic material, preferably from Aluminum. These parts may be manufactured by any suitable process, such as milling, casting, laser cut, CNC, etc. Body 30a of robot 30 is preferably a 0.7 ^χ l meters frame made from aluminum profiles having a cross sectional area in the range of 40*700 mm.

Fig. 5 is a block diagram schematically illustrating a preferred pneumatic control scheme for the linear actuators of the robot. Streams of pressurized air contained in air tank 18 are flown to a specific actuator 47 by means of controllable valve manifold 12. The pressurized air is flown from air tank 18 through tube 18p to controllable valves provided in manifold 12 from which pressurized air streams are directed to selected actuators according to control signals 12c received from controller 13. The pressurized air is directed via the respective air outlet 12o into tube 12p connecting said outlet to a respective actuator operating mechanism 43.

Actuator operating mechanism 43 comprises a 5/3 controllable pneumatic valve 40 (e.g., Baccara 27522412), one-way-valve 46

(e.g., T valve, such as Baccara 21731654), and two pneumatic normally-closed valves 41 and 42 (e.g., Baccara 21752220). Actuator operating mechanism 43 is pneumatically connected to actuator 47 which comprises extraction sensor 48 adapted to provide indicating signals 48s to controller 13 responsive to the extracted length of moving shaft 47s.

The 5/3 controllable pneumatic valve 40 is a three state valve having five pneumatic ports, one of which is used as air inlet 4Oi, two other ports (not shown) are used as air discharge ports, and the remaining two ports are used as air outlets 40ol and 40o2. The states of 5/3 controllable pneumatic valve 40 are determined by control signals received via control inputs 40sl and 40s2. Air outlets 40ol and 40o2 of 5/3 controllable pneumatic valve 40 are connected to air inlets 41i and 42i of normally-closed valves 41 and 42, respectively, by means of respective tubes, 40pl and 40p2. The air outlets of normally-closed valves 41 and 42 are connected by tubes to pneumatic ports 47i2 and 47il, respectively, through which the chambers 47cl and 47c2 of actuator 47 may be respectively accessed. The volumes of actuator's chambers 47cl and 47c2 are determined by the location of plunger 47p along its length.

One-way-valve 46 is preferably a type of T-valve (pneumatic OR gate) having two one way air inlets 46x1 and 46i2, and one air outlet 46o. The state of pneumatic normally-closed-valves 41 and 42 is determined according to the pneumatic output provided from air outlet 46o of one-way-valve 46, such that whenever a stream of pressurized air is provided to one of its air inlets, 46il or 46x2, the state of normally-closed- valves 41 and 42 is changed into their "open" state and paths

therethrough from chamber ports 47il and 47i2 to the respective tubes 40pl and 40p2 is thereby provided.

In this way moving shaft 47s of pneumatic actuator 47 may be extracted/retracted by providing appropriate control signals 12c to valve manifold 12 for selecting a specific actuator, and respective control signal 40sl or 40s2 for extracting or contracting, respectively, moving shaft 47s.

Air tank 18 is preferably a type of pressure vessel made from Stainless steel, steel, or Aluminum, or any other suitable metal alloy, having a suitable volume. Controllable valve manifold 12 may be implemented by standard controllable pneumatic manifolds comprising 12 controllable valves, preferably 5/3 valves, such as, for example Baccara 27522412.

Fig. 7 illustrates a preferred embodiment of a quadruped robot 40 of the invention wherein universal joints 37n (Fig. 7C) are used for attaching actuators 35a (Fig. 7B) of legs 35 to the robot body 40a. In this preferred embodiment the longitudinal motion actuators 36r and lateral motion actuators 36q (Fig. 7A) are attached to legs 35 and body 40a by means of rod-end spherical bearing joints 37s, it should be however understood that universal joint 37n may similarly used for connecting actuators 36r and 36q.

With reference to Fig. 6, in the preferred embodiment of the invention the control system of the four-legged robot is composed of the following hardware and software components: i) Localization System 61: this component is composed of a Global Positioning System (GPS) and an Inertial Measurement Unit (IMU) . The IMU unit is based on three-axis acceleration sensor (s) and three-axis rate gyroscope (e.g., a Crossbow

technology NAV 420CA IMU) . The data form these two sensors is combined to provide the location and orientation of the robot. ii) Location and orientation of the robot is provided as inputs to the Motion Planning System 62 (e.g., processing means such as Panasonic Toughbook) . The motion planning system 62 is preferably operated by means of a map (e.g., three-dimensional terrain map) of the environment and an obstacle detection sensor 63 for detecting possible obstacles along the robot's path. The obstacle sensor 63 may be implemented as a stereo vision system, a laser scanner, or radar (e.g., Point Grey Research digiclops, Sick Laser Scanner LMS 221-30206, FMCW-Radar (A. Foessel 2000)). The motion planning system 62 also receives information from the user on the exact destination of the robot motion, and on one or more navigation routes for approaching it. Then the motion planning system 62 decides what should be the actual extraction length of the moving shafts in the pneumatic actuators at every instance. iii) The Controller 13 (e.g., processing means such as Panasonic Toughbook, Schneider Electric Twido controller) receives the desired extraction lengths of moving shafts of the pneumatic actuators and the actual extracted length of each of said shafts as measured by extraction sensor (48 in Fig. 5), which are preferably a type of potentiometers (e.g., Spectrum sensors & control Inc. model 5903) , optical encoders (e.g. Encodertech LM720CPI-3T) or LVDTs (Linear Variable Differential Transformer e.g., Sentech Inc. model 75PCDC) . The controller 13 may also receive measurements of the contact force or the pressure in every pneumatic cylinder by, means of a pressure sensor such as Omega.com PXM219-010G10V pressure sensor.

iv) Using these inputs the controller 13 determines which Control Valves (e.g., Baccara model 5320) should be opened and which should be closed . v) According to these determinations the control valves close or open the air flow to and from the Pneumatic actuators (e.g., Baccara air cylinder model MGQ).

Controller 13 may be implemented by means of a computer (e.g., personal computer with a Pentium processor) equipped with one or more memory devices, such as, hard disks, NV-RAM, flash memories, for storing data (e.g., terrain maps), and computer software associated with the robot motion, and/or any other required data or software. The control system of the robot may further comprise a RF receiver, or transceiver, for receiving remote control signals, or for changing navigation paths during operation. RF transmission may be employed by the robot to transmit various types of information to a remote user, such as, for example, status and location indications, how much fuel is left in fuel tank 9, and/or the status of a power source 14.

Data acquisition means (e.g., National Instruments DAQ-Pad) and A/D and D/A conversion means (e.g., Phidget InterfaceKit 8/8/8) are typically used to interface between controller 13 and the various sensors and controllable valves. These are standard components to be used in a conventional manner and thus they will not be discussed herein in details for the sake of brevity.

Though in the embodiments described hereinabove spherical joints and rod-end spherical bearing joints were employed, it should be understood that other types of joints may be similarly employed. In fact, in a specific preferred

embodiment of the invention the legs and the actuators are attached in the robot by means of universal joints, such as Emerson-ept UMDN50-4*β-100D.

A motion planning algorithm that solves the associated path planning problem is preferably a search algorithm that finds a path under the equilibrium and reachability constraints. That is, in quasi-static motion planning the robot should be in a static equilibrium in every instance along the path. In addition every point along the path should be a feasible configuration of the robot in the sense that the configuration can be admitted by the mechanism under structural design and joints angle/length limitations.

The four-legged robot of the invention generally consists of four legs each equipped with three DOFs, and of a central body that has additional six un-actuated DOFs (translation and rotation of the central body as a single rigid body) . Thus the c-space (configuration space) dimension of the four- legged robot of the invention is eighteen. Current state of the art motion planning algorithm (e.g., Choset et al. 2005) can find a path in not more than three-dimensional c-spaces. Therefore the problem of finding a path in the robot's eighteen dimensions c-space should be treated differently. For example, two possible options to solve this problem are : 1) First, to decompose the problem into two sub-problems. The first sub-problem is to find a sequence of contact points on the ground. Then the second sub-problem is finding a path for all the actuated joints that will move the robot from each set of contact points to the following one. Hence this methodology generates a 3-4-3 gait in which the robot stands on only 3 legs and reach with the forth leg to a new foothold position. Then the robot move its central body forward to

advance the location of the robot's center of mass, and finally the robot lift off another leg and move it to a new foothold position. This sequence is being repeated over and over again while the robot moves .

2) A second option for the motion planning is to select a specific gait pattern for the mechanism. A gait is a way of moving the legs in order to locomote, and gait pattern is the specific sequence of foots attach and detach the ground. A gait pattern is governed by few parameters such as step size, step duration, phase difference between the legs motion, etc. Then the motion planning system adjusts the gait parameters according to the changes in the environment. Accordingly, a feasible path in the gait parameters space is searched and then, by using the gait definition, the actual configuration associated with every instance of the gait can be computed.

It should be noted that the quadruped robot of the invention may be configured for exhibiting various gaits types, including, but not limited to, walking, running and jumping.

The control algorithm of the robot is preferably designed to assure that even if the robot deviates from the designed path it will eventually return to this path. A basic and simple way to achieve this goal is by guaranteeing asymptotic stability of all points along the trajectory. An asymptotically stable state of the robot is a state that attracts all neighboring states. Hence the control strategy may be based on discretizing the path into waypoints. Then, if the robot is located at its' initial state and the controller assure that the next point on the discretized path is asymptotically stable the flow of the robot's dynamical system will drive the robot toward the next point on the path. If then the controller will insure that this point is

no longer stable and it will assure that the next point on path is stable then the robot will continue to move along the path toward the third point, and so on for the entire path. This method is the common trajectory tracking method in robotics while having set-point stable controllers. This method is also assured to work as long as the previous state is within the basin of attraction of the next state.

All of the abovementioned parameters are given by way of example only, and may be changed in accordance with the differing requirements of the various embodiments of the present invention. Thus, the abovementioned parameters should not be construed as limiting the scope of the present invention in any way.

The above examples and description have of course been provided only for the purpose of illustration, and are not intended to limit the invention in any way. As will be appreciated by the skilled person, the invention can be carried out in a great variety of ways, employing more than one technique from those described above, all without exceeding the scope of the invention.