Foot system for jointed leg type walking robot

An improved foot system for a jointed leg type walking robot capable of more stably walking on both even and uneven ground surfaces by providing a jointed leg type foot system with a front toe cylinder and a rear toe cylinder each communicated with a front toe assembly and a rear toe assembly. In addition, it is capable of more stably landing on uneven ground surface and absorbing landing impacts more efficiently, which includes a lower foot body; an upper foot body mounted on the top of said lower foot body; a gas accumulator formed within the lower foot body; a front toe assembly pivotally attached to a predetermined portion of the lower foot body; and a rear toe assembly pivotally attached to a predetermined portion of the lower foot body.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a foot system for a jointed leg type 
walking robot, and particularly to an improved foot system for a jointed 
leg type walking robot capable of more stably walking on both even and 
uneven ground surfaces by providing a jointed leg type foot system with a 
front toe cylinder and a rear toe cylinder each communicated with a front 
toe assembly and a rear toe assembly, respectively. 
2. Description of the Conventional Art 
In the industrial field, the use of robots increases strongly for handling 
harmful chemicals, radioactive materials and the like which are very 
dangerous to humans. Among the methods of enabling a robot to move upon 
the ground, a method of using a jointed leg type walking system has been 
introduced. For the jointed leg type foot system, a flat or circular plate 
has been used, however the trial of improving the structure of a foot 
system is not introduced. 
Referring to FIG. 1, there is shown a construction of a conventional 
jointed leg type walking robot. As shown therein, the robot is provided 
with a head 1 equipped with a visual sensor 2 mounted at a predetermined 
portion thereof. An upper body 3, a predetermined upper portion of which 
is pivotally connected to a predetermined portion of the head 1, is 
provided with a pair of arms 4. One end of each arms 4 is pivotally 
connected to a respective side of the upper body 3 and the other ends 
thereof are each pivotally provided with a hand 5. A bottom surface of the 
upper body 3 is rotatably connected to a predetermined portion of a lower 
body 6. A front waist joint 7 is rotatably connected to a predetermined 
forward portion of the lower body 6. A rear waist joint 8 is also 
rotatably connected to a predetermined rearward portion of the lower body 
6. An upper end of each of a pair of front hip joints 9 is pivotally 
connected to a predetermined portion of the front waist joint 7 and a 
lower end of each front hip joints is pivotally connected to a front knee 
joint 10 which is also pivotally connected to a front ankle joint 11. 
Here, each front ankle joint 11 is pivotally provided with a front foot 
12, the bottom surface of which is directed to contacting with an even 
ground surface 17. Meanwhile, the rear legs consists of the same structure 
as the front legs, so the descriptions thereof are omitted. 
What kind of problem a jointed leg type walking robot with conventional 
foots can have, will now be explained with reference to FIG. 1 and FIGS. 
2A to 2D. 
To begin with, the robot performs some task in accordance with a control 
signal outputted from a microcomputer (not shown) mounted at a 
predetermined portion thereof, receiving a visual signal outputted from 
the visual sensor 2. Here, the walking operation of the robot is also 
conducted by a combined moving operation of the front/rear waist joints 7 
and 8, the front/rear hip joints 9 and 13, and the front/rear knee joints 
10 and 14, the front/rear ankle joints 11 and 15, and the front/rear feet 
12 and 16. Here, since each foot 12, 16 is pivotally connected to each 
ankle joint 11, 15, it is generally required that each of the bottom 
surfaces thereof is always facing parallel with the even ground surface, 
so that the stable walking operation without slippage on the ground 
surface can be achieved. 
However, as are well shown in FIGS. 2A to 2D, the conventional foot system 
has disadvantages in that the robot often slips on uneven ground surfaces 
due to its pivotal moment at the front/rear ankle joints 11 and 15, which 
occurs when a foot 12, 16 lands on an uneven ground surface or moves the 
body forwards during the support phase. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a foot 
system for a jointed leg type walking robot. 
It is another object of the present invention to provide an improved foot 
system for a jointed leg type walking robot capable of more stably walking 
on both even and uneven ground surfaces by providing a jointed leg type 
foot system with a front toe cylinder and a rear toe cylinder each 
communicated with a front toe assembly and a rear toe assembly. In 
addition, it is capable of more stably landing on uneven ground surface 
and absorbing landing impacts more efficiently. 
To achieve the above objects, there is provided a foot system for a jointed 
leg type walking robot, which includes a lower foot body; an upper foot 
body mounted on the top of said lower foot body; a gas accumulator formed 
within the lower foot body; a front toe assembly pivotally attached to a 
predetermined portion of the lower foot body; and a rear toe assembly 
pivotally attached to a predetermined portion of the lower foot body.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 3, a foot system for a jointed leg type 4-legged walking 
robot is provided with a lower foot body 100, an upper foot body 200 
fitted to the lower foot body 100, a gas accumulator 300 centrally 
downwardly formed within the lower foot body 100, a front toe assembly 
400, and a rear toe assembly 500. 
The front and rear sides of the lower foot body 100 are respectively 
provided with integrally shortened and downwardly and outwardly extending 
front and rear bracket portions 101, 102, the upwardly and outwardly 
angled bottom surfaces of which define front and rear shoulders 103, 104 
with the recessed lower outer peripheral surface of the lower foot body 
100. Within each front and rear bracket portions 101, 102 there are 
centrally formed a downwardly and outwardly inclined front and rear toe 
cylinder 105, 106 each opened at their bottom end to the thusly defined 
front shoulder 103 (not shown) and rear shoulder 104, and having their 
closed upper ends each communicated with front and rear oil lines 105b, 
106b to the upper surface of the lower foot body 100 atop which abuts the 
bottom surface of a horizontally formed oil path section 202 of the upper 
foot body 200. 
The upper foot body 200 includes an engaging section 201 having a threaded 
portion 201a which is formed on the outer circumferential surface thereof 
and an oil path section 202 integrally formed with the engaging section 
201. 
Here, the oil path section 202 includes an oil path 203 horizontally formed 
within the oil path section 202, the front and rear portion of which is & 
communicated with each of front and rear toe cylinder oil chambers 105a, 
106a of the front and rear toe cylinders 105, 106 through a front and rear 
oil lines 105b, 106b. In addition, the central portion of the oil path 203 
is connected to a gas accumulator oil chamber 301 through a central oil 
line 302 and a damping orifice 303 in order. 
A gas accumulator 300 is centrally provided within the lower foot body 100. 
A gas accumulator oil chamber 301 is formed in the upper portion thereof. 
A piston 304 having a pair of piston rings 304 inserted onto an outer 
circumferential surface thereof reciprocates in the gas accumulator 300. A 
gas chamber 305 is formed below the piston 304. A gas chamber shoulder 307 
is formed between the gas accumulator oil chamber 301 and the gas chamber 
305 so as to limit the movement of the piston 304. 
A gas filling assembly 306 including a gas filling port 306a connected 
between the gas chamber 305 and the sealing screw 306b and mounted on the 
bottom thereof is provided below the gas chamber 305 for charging gas into 
the gas chamber 305. 
In addition, each outwardly downwardly formed toe cylinder 105, 106 
includes cylinder oil chambers 105a, 106a centrally formed therewithin. 
Each toe piston 105c, 106c is disposed in each toe cylinder 105, 106, 
respectively. A front/rear toe rollers 107, 108 each rotatably engaged 
with a front/rear roller pins 107a, 108a are disposed on each bottom of 
the front and rear toe pistons 105c and 106c. The circumferential surfaces 
of the front/rear toe rollers 107, 108 come into rolling contact with a 
front/rear toe bracket guide surfaces 406, 506. In addition, seals 109, 
110 are respectively mounted on an inner circumferential surface of each 
toe cylinder 105, 106 within the lower foot body 100. 
A front toe assembly 400 is disposed in front of the lower foot body 100, 
and a rear toe assembly 500 is disposed behind the lower foot body 100. 
The front toe assembly 400 includes a downwardly outwardly standing front 
toe 401. Here, the front/rear toe 401, 501 has a front/rear toe front side 
401a, 501a, a front/rear toe rear side 401b, 501b, a front/rear toe first 
side 401c, 501c, and a front/rear toe second side 401d, 501d (not shown). 
The upper end of the front/rear toe 401, 501 is pivotally connected to one 
end of the front/rear toe upper link 402, 502 by a front/rear toe first 
upper pin 402a, 502a. The other end of the front/rear toe upper link 402, 
502 is also pivotally connected to a predetermined portion of the lower 
foot body 100 by a front/rear toe second upper pin 402b, 502b. A 
predetermined portion of the front/rear toe 400, 500 is pivotally 
connected to one end of a front/rear toe lower link 403, 503 by a 
front/rear toe first lower pin 403a, 503a. The other end of the front/rear 
toe lower link 403, 503 is also pivotally connected to a predetermined 
portion of the lower foot body 100 by a front/rear toe second lower pin 
403b, 503b. 
A downwardly outwardly extended front/rear toe bracket 404 (not shown), 504 
having a downwardly inwardly slanted front/rear toe roller guide 404a, 
504a, on which the front/rear toe rollers 107, 108 come into rolling 
contact, is mounted on the front/rear toe rear side 401b, 501b. 
On each of the front/rear toes 401, 501, a tip 405, 505 is attached to each 
of the front/rear toes 401, 501 to protect the front/rear toes 401, 501 
from the shock damages caused when the robot walks on the ground surface. 
To begin with, an operation of a foot system for a jointed leg type 
4-legged walking robot according to the present invention will now be 
explained with reference to FIGS. 4A through 4E. 
Of which, FIG. 4A shows the foot system when the foot is lifted during the 
leg-swing phase of the leg and the front and rear toe assembly thereof are 
fully extended by the gas pressure. FIG. 4B shows the foot system when the 
rear toe is pushed upwards to its neutral position. Then, the oil is 
forced to flow from rear toe cylinder 106 to the gas accumulator 300 
through the damping orifice 303. In this case, the gas accumulator piston 
moves downwards to its middle position from the upper limit, compressing 
the gas. FIG. 4C shows the foot system when the rear toe is pushed upwards 
to its upper limit making the gas accumulator piston move to its lower 
limit by the discharged oil from the rear toe cylinder 106. Since the gas 
accumulator piston is at its lower limit, the front toe 401 can not be 
pushed upwards. But the foot can be rotated without restriction, as the 
oil can flow from the front toe cylinder 105 into the rear toe cylinder 
106 freely. FIG. 4D shows the foot system when both the front and rear 
toes 401 and 501 are in the neutral position. When e.g. the foot is 
rotated clockwise to its upright position in FIG. 4C with the gas 
accumulator piston at its lower limit. FIG. 4E shows the foot system when 
the foot is rotated further in FIG. 4, making the rear toe 501 moves to 
its lower limit and the front toe 401 moves to its upper limit also with 
the gas accumulator piston at its lower limit. It is to be noted that the 
imaginary connecting line between the two toe tips has the center of 
rotation at its middle position during the change of the state from FIG. 
4C through FIG. 4E. 
In addition, FIG. 5A through FIG. 5F show an operation of the foot system 
and a leg of the robot according to the present invention. 
Of which, FIG. 5A shows the foot system when the fully lifted foot is on 
the point of landing after the swing phase of the leg. the working state 
of the foot is shown in FIG. 4A. FIG. 5B shows the foot system when the 
foot is at the beginning of the landing phase. The rear toe touches the 
ground at first and is pushed upwards by the weight of the robot body as 
shown in FIG. 4B. During this working phase of the foot the landing impact 
energy will be changed into heat energy by the damping orifice 303 through 
which the oil from the rear toe cylinder 106 flows into the accumulator. 
The amount of the absorbed energy is proportional to the oil flow rate 
through the damping orifice 303 multiplied by the pressure drop across it, 
which in return proportional to the square root of the flow rate. FIG. 5C 
shows the foot system when the foot is completely landed using the rear 
toe. The working state of the foot us shown in FIG. 4C and the landing 
impact absorbing function of the foot is no more effective. The initial 
charge pressure of the gas chamber 305 should be determined so that the 
pressure of the gas chamber 305 can keep the equilibrium with the load 
pressure by the body weight, when its volume is minimum. FIG. 5D shows the 
foot system when the leg and the foot are rotated clockwise to its upright 
position during the supporting phase of the foot. The working state of the 
foot is shown in FIG. 4D. FIG. 5E shows the foot system when the foot is 
rotated further at the end of the supporting phase. The working state of 
the foot is shown in FIG. 4E. FIG. 5F shows the foot system when the foot 
is at the beginning of the swing phase of the leg. The working state of 
the foot is similar to that shown in FIG. 4A, except that the front toe 
401 is in its neutral position. 
FIGS. 6A through 6D show an operation of the foot system and a leg of the 
robot on uneven ground surface according to the present invention. 
Of which, FIG. 6A shows the foot system when the foot is at the beginning 
of the landing phase as shown in FIG. 5B. The rear toe can be landed on 
uneven surface safe and firm with high probability, since it contacts the 
ground surface with small area. FIG. 6B shows the foot system when the 
foot is completely landed using the front and rear toes 401 and 501 as 
shown in FIG. 5C. similar to the rear toe, the front toe 401 also can be 
landed on uneven surface safe and slipless with high probability. FIG. 6C 
shows the foot system when the leg and the foot are rotated clockwise to 
its upright position during the supporting phase of the foot as shown in 
FIG. 5D. Since the center of rotation of the foot lies on the ground 
surface, the contact points of the front and rear toe with the ground 
surface remain unchanged. FIG. 6D shows the foot system when the foot is 
rotated further at the end of the supporting phase as shown in FIG. 5E. 
Next, FIG. 7 shows a trajectory of a movement of each toe assembly of the 
foot system according to the present invention. 
As shown therein, F1 denotes a point of the front toe second upper pin 
402b, F2 denotes a point of the front toe second lower pin 403b, F3, F3', 
F3" denote points of the front toe first upper pin 402a, F4, F4', F4" 
denote points of the front toe first lower pin 403a, and F5, F5', F5" 
denote bottom end points of the front toe 400. In addition, F1R denotes a 
radius distance between F1 and F3. F2R denotes a radius distance between 
F2 and F4. 
Meanwhile, R1 denotes a point of the rear toe second upper pin 502b, R2 
denotes a point of the rear toe second lower pin 503b, R3, R3', R3" denote 
points of the rear toe first upper pin 402a, R4, R4', R4" denote points of 
the rear toe first lower pin 503a, and R5, R5', R5" denote bottom end 
points of the rear toe 500. In addition, R1R denotes a radius distance 
between R1 and R3. R2R denotes a radius distance between R2 and R4. In 
addition, "C" denotes a center between F5, F5, F5" and R5, R5', R5". 
The operation of the foot system of the robot with above described points 
will now be explained. 
When the foot is fully lifted during the swing phase of the leg, the front 
and rear toe are fully extended as shown in FIG. 4A. At this time, FIG. 3 
and R3 move downwards up to the point of F3" and R3" with having the 
radius of F1R and R1R, respectively. At the same time, F4 and R4 move 
downwards up to the points of F4" and R4" with having the radius of F2R 
and R2R, respectively. 
When the robot body's weight is applied to the rear toe 501 during the 
landing phase of the foot, as shown in FIG. 4B and FIG. 4C, R3" move up to 
the point of R3' via R3 with the radius of R1R. R4" moves up to the point 
of R4' via R4 with the radius of R2R. R5" moves up to the point of R5' via 
R5 with the radius of CR. 
When the robot body's weight is applied to the rear toe 501 and front toe 
401 equally and the foot is standing vertically during the supporting 
phase, as shown in FIG. 4D, R3' moves to the point of R3 with the radius 
of R1R. R4' moves to the point of R4 with the radius of R2R. R5' moves up 
to the point of R5 with the radius of CR. On the contrary, F3" moves up to 
the point of F3 with the radius of F1R. F4" moves up to the point of F4 
with the radius of F2R. F5" moves up to the point of F5 with the radius of 
CR. 
When the robot body's weight is applied to the front toe 401 at the end of 
the support phase, as shown in FIG. 4E, R3 moves to the point of R3" with 
the radius of R1R. R4 moves to the point of R4" with the radius of R2R. R5 
moves up to the point of R5" with the radius of CR. On the contrary, F3 
moves up to the point of F3' with the radius of F1R. F4 moves up to the 
point of F4' with the radius of F2R. F5 moves up to the point of F5' with 
the radius of CR. 
In this way described above, the foot has its center of rotation located on 
the ground surface which allows the elimination of the ankle joint, the 
contact points of the toes with ground surface do not change during the 
rotation of the foot, and the contact angle between the toe pistons and 
the toe bracket guiding surface can be kept nearly 90 degree during the 
movement of toes so that the toe pistons can be free of the side reaction 
force from toes which can cause sticktion of the piston. As the trajectory 
of the toe movement lies within a narrow band, the hydraulic force of the 
toe pistons acting on the top tips remains almost constant during the 
rotation of the foot, which assures same supporting force of the front and 
rear toes. 
FIG. 8 shows an example of experimental results obtained by the measurement 
of the landing force on the foot when a jointed-leg type foot is walking 
with a conventional foot in the form of a circular plate, and with the 
foot according to the present invention. 
As is shown, in the case of the conventional foot is the form of circular 
plate the landing force indicates sharper increasing rate and higher peak 
value than the foot according to the present invention. FIG. 9 shows the 
movement of the toes under the same experimental condition. As is shown, 
firstly, the rear toe moves upwards when it touches the ground and during 
the rotation of the foot, the rear toe moves downwards while the front toe 
moves upwards. 
Although the preferred embodiments of the present invention have been 
disclosed for illustrative purposes, those skilled in the art will 
appreciate that various modifications, additions and substitutions are 
possible, without departing from the scope and spirit of the invention as 
described in the accompanying claims.