Title: Leg joint assist device for leg type movable robot
Abstract: An assist device that applies an auxiliary driving force to a joint in parallel with a driving force of a joint actuator between a thigh portion and a crus portion, which are a pair of link members of a leg. The assist device generates the auxiliary driving force by use of spring device, such as a solid spring or an air spring. A member supporting a rod member connected to the spring device is provided with a device for transmitting a bending and stretching motion of the leg at the joint (a relative displacement motion between the thigh portion and the crus portion) to the spring device to generate an elastic force of the spring device, and for discontinuing the transmission of the bending and stretching motion to the spring device. This transmitting device is controlled in accordance with a gait of a robot. Thus, a burden on the joint actuator is reduced where necessary and favorable utilization efficiency of energy can be stably ensured.
Patent Number: 6,962,220 Issued on 11/08/2005 to Takenaka, et al.
| Inventors:
|
Takenaka; Toru (Wako, JP);
Gomi; Hiroshi (Wako, JP);
Hamaya; Kazushi (Wako, JP);
Takemura; Yoshinari (Wako, JP);
Matsumoto; Takashi (Wako, JP);
Yoshiike; Takahide (Wako, JP);
Nishimura; Yoichi (Wako, JP);
Akimoto; Kazushi (Wako, JP)
|
| Assignee:
|
Honda Giken Kogyo Kabushiki Kaisha (Tokyo, JP)
|
| Appl. No.:
|
490802 |
| Filed:
|
September 24, 2002 |
| PCT Filed:
|
September 24, 2002
|
| PCT NO:
|
PCT/JP02/09757
|
| 371 Date:
|
March 25, 2004
|
| 102(e) Date:
|
March 25, 2004
|
| PCT PUB.NO.:
|
WO03/028960 |
| PCT PUB. Date:
|
April 10, 2003 |
Foreign Application Priority Data
| Sep 27, 2001[JP] | 2001-298677 |
| Current U.S. Class: |
180/8.6; 700/260; 901/1; 901/9; 901/2; 318/568.12; 180/8.1; 74/490.01 |
| Intern'l Class: |
G06F 019/00 |
| Field of Search: |
180/81,85,86
901/1,2,9,46
700/245,246,254,260,261
318/568.11,568.12,568.16,568.2
74/490.01,490.03,490.05
|
References Cited [Referenced By]
U.S. Patent Documents
| 5808433 | Sep., 1998 | Tagami et al.
| |
| 6401846 | Jun., 2002 | Takenaka et al.
| |
| 6564888 | May., 2003 | Gomi et al.
| |
| 6802382 | Oct., 2004 | Hattori et al.
| |
| 2004/0261561 | Dec., 2004 | Takenaka et al.
| |
| Foreign Patent Documents |
| 11-300660 | Nov., 1999 | JP.
| |
| 2001/-198864 | Jul., 2001 | JP.
| |
| 2001/-287177 | Oct., 2001 | JP.
| |
Primary Examiner: Luby; Matthew
Attorney, Agent or Firm: Rankin, Hill, Porter & Clark LLP
Claims
1. A leg joint assist device for generating an auxiliary driving force on a specific
joint of a legged mobile robot in parallel with a driving force of a joint actuator
driving the specific joint, the robot comprising a plurality of legs, extending
from a body, configured by connecting a plurality of link members sequentially
from a body side through the plurality of joints, wherein at least one joint amongst
a plurality of the joints of each of a plurality of the legs is defined as the
specific joint in the legged mobile robot, the leg joint assist device comprising:
spring means, provided to be able to transmit a relative displacement motion
of a pair of the link members connected by the specific joint, the relative displacement
motion being caused by actuation of the specific joint, for generating the auxiliary
driving force while storing elastic energy in synchronization with the relative
displacement motion in a state where transmission of the relative displacement
motion is continued, and for restoring a state where the elastic energy is released
in a state where transmission of the relative displacement motion is discontinued;
motion transmission continuation/discontinuation means for continuing and discontinuing
transmission of the relative displacement motion of the pair of link members to
the spring means; and
control means for controlling continuation/discontinuation of transmission of
the relative displacement motion to the spring means by the motion transmission
continuation/discontinuation means, depending on a state of motion of each of the legs.
2. The leg joint assist device according to claim 1, wherein the control means
controls the motion transmission continuation/discontinuation means to discontinue
transmission of the relative displacement motion of the pair of link members to
the spring means at least during a first predetermined period in a state where
each of the legs is lifted off a floor.
3. The leg joint assist device according to claim 1, wherein, while the legged
mobile robot is moving with a predetermined gait which has been decided in advance,
the control means controls the motion transmission continuation/discontinuation
means to continue transmission of the relative displacement motion of the pair
of link members to the spring means at least during a second predetermined period
in a state where each of the legs lands on the floor.
4. The leg joint assist device according to claim 3, wherein the second predetermined
period in the state where each of the legs lands on the floor is determined such
that relative displacement amounts between the pair of link members at start time
and stop time of the second predetermined period are approximately equal.
5. The leg joint assist device according to claim 3, comprising means for controlling
a driving force of the joint actuator such that, while the motion transmission
continuation/discontinuation means is continuing transmission of the relative displacement
motion of the pair of link members to the spring means, a sum of the auxiliary
driving force by the spring means and the driving force of the joint actuator becomes
a desired driving force determined to follow a desired gait of the legged mobile robot.
6. The leg joint assist device according to claim 5, wherein the means for controlling
the driving force of the joint actuator estimates the auxiliary driving force by
the spring means based on a variation of the relative displacement amount between
the pair of link members from the start time of the second predetermined period
and characteristic data of the auxiliary driving force of the spring means, which
is obtained in advance.
7. The leg joint assist device according to claim 1, wherein the spring means
is a gas spring which elastically generates the auxiliary driving force by compression
or expansion of gas.
8. The leg joint assist device according to claim 1, wherein the joint actuator
is an electric motor.
9. The leg joint assist device according to claim 2, wherein, while the legged
mobile robot is moving with a predetermined gait which has been decided in advance,
the control means controls the motion transmission continuation/discontinuation
means to continue transmission of the relative displacement motion of the pair
of link members to the spring means at least during a second predetermined period
in a state where each of the legs lands on the floor.
10. The leg joint assist device according to claim 9, wherein the second predetermined
period in the state where each of the legs lands on the floor is determined such
that relative displacement amounts between the pair of link members at start time
and stop time of the second predetermined period are approximately equal.
11. The leg joint assist device according to claim 9, comprising means for controlling
a driving force of the joint actuator such that, while the motion transmission
continuation/discontinuation means is continuing transmission of the relative displacement
motion of the pair of link members to the spring means, a sum of the auxiliary
driving force by the spring means and the driving force of the joint actuator becomes
a desired driving force determined to follow a desired gait of the legged mobile robot.
12. The leg joint assist device according to claim 11, wherein the means for
controlling the driving force of the joint actuator estimates the auxiliary driving
force by the spring means based on a variation of the relative displacement amount
between the pair of link members from the start time of the second predetermined
period and characteristic data of the auxiliary driving force of the spring means,
which is obtained in advance.
13. The leg joint assist device according to claim 9, wherein the spring means
is a gas spring which elastically generates the auxiliary driving force by compression
or expansion of gas.
14. The leg joint assist device according to claim 9, wherein the joint actuator
is an electric motor.
Description
TECHNICAL FIELD
The present invention relates to a leg joint assist device which generates an
auxiliary driving force to a joint of a leg of a legged mobile robot such as a
biped mobile robot, to assist a joint actuator which is for driving the joint.
BACKGROUND ART
In a legged mobile robot with a plurality of legs, each of the legs is configured
by sequentially connecting a plurality of link members through a plurality of joints
from a body. For example, in a biped mobile robot with two legs like a human, each
of the legs is configured by sequentially connecting the link members, which correspond
to a thigh portion, a crus portion, and a foot portion, through a hip joint, a
knee joint, and an ankle joint, respectively, from a body of the robot. In addition,
in the legged mobile robot of this kind, a motion of each of the legs for moving
the robot is produced by applying a driving force (torque) to each of the joints
of each of the legs by using a joint actuator such as an electric motor.
Incidentally, in the mobile robot of this kind, when, for example,
a movement speed thereof is increased, forces (moment) acting on the joints of
each of the legs are likely to be relatively large in a foot landing state of each
of the legs (a state of a supporting leg period of each of the legs), due to floor
reaction forces or the like. Consequently, driving forces (torque), which should
be generated to the joint actuators to resist the forces, are likely to be relatively
large. For example, in a case of allowing the biped mobile robot to run with a
gait (a motion pattern of legs) similar to the gait of a running human, the driving
force to be generated to the joint actuator of the knee joint becomes large, particularly
in a supporting leg period of each of the legs, according to the knowledge of the
inventor and the like. In this case, when the joint actuator is an electric motor,
the aforementioned driving force is generated by a regenerative operation or a
powering operation of the electric motor. With any of these operations, however,
it is required to energize the electric motor or a power source such as a battery
with a high current. Thus, an energy loss by Joule heat or the like is likely to
be large. Further, since the electric motor with a large capacity is required,
the size and weight of the electric motor become large.
Meanwhile, as disclosed in Japanese Patent Laid-Open Publication No. 2001-198864
(especially FIG. 9 of this publication), for example, a biped mobile robot is known
in which a spring is provided between two link members (a thigh portion and a crus
portion) connected by a knee joint of each leg.
While moving horizontally, this biped mobile robot converts kinetic energy
in the horizontal direction of the robot into elastic energy of the spring and
stores the elastic energy, thus producing a jumping motion of the robot by the
use of the elastic energy. In the biped mobile robot provided with the springs
as above, a part of a driving force to be generated in each of the knee joints
is provided by the elastic force of the spring during a part of the period when
the robot is in the running motion or the like. Thus, a burden on the joint actuators
of the knee joints can be reduced. However, in this biped mobile robot, the elastic
force of the spring is always acting between the thigh portion and the crus portion
of each of the legs. Therefore, while the biped mobile robot is moving, a situation
occurs where the elastic force of the spring acts in an opposite direction to the
driving force which should be generated in each of the knee joints. In such a situation,
a driving force generated to the joint actuator of each of the knee joints becomes
unnecessarily large. As a result, it becomes difficult to improve utilization efficiency
of the total energy of the robot.
The present invention was accomplished in light of the above-described circumstances,
and it is an object of the present invention to provide a leg joint assist device
for a legged mobile robot, which is enabled to reduce burdens on joint actuators
as necessary and to stably ensure favorable utilization efficiency of energy.
DISCLOSURE OF THE INVENTION
A novel leg joint assist device for a legged mobile robot is a leg joint assist
device for generating an auxiliary driving force on a specific joint of a legged
mobile robot in parallel with a driving force of a joint actuator driving the specific
joint, the robot comprising a plurality of legs, extending from a body, configured
by connecting a plurality of link members sequentially from a body side through
the plurality of joints, wherein at least one joint amongst a plurality of the
joints of each of a plurality of the legs is defined as the specific joint in the
legged mobile robot, the leg joint assist device comprising: spring means, provided
to be able to transmit a relative displacement motion of a pair of the link members
connected by the specific joint, the relative displacement motion being caused
by actuation of the specific joint, for generating the auxiliary driving force
while storing elastic energy in synchronization with the relative displacement
motion in a state where transmission of the relative displacement motion is continued,
and for restoring a state where the elastic energy is released in a state where
transmission of the relative displacement motion is discontinued; motion transmission
continuation/discontinuation means for continuing and discontinuing transmission
of the relative displacement motion of the pair of link members to the spring means;
and control means for controlling continuation/discontinuation of transmission
of the relative displacement motion to the spring means by the motion transmission
continuation/discontinuation means, depending on a state of motion of each of the legs.
According to the present invention described above, the leg joint assist
device includes the motion transmission continuation/discontinuation means for
continuing/discontinuing transmission of the relative displacement motion of the
pair of link members, caused by the actuation of the specific joint, to the spring
means. Further, in a state where transmission of the relative displacement motion
of the pair of link members is discontinued, the spring means restores the state
where the elastic energy is released (a state equivalent to a natural length state
of a coiled spring). Thus, by controlling the motion transmission continuation/discontinuation
means by use of the control means depending on the state of motion of each of the
legs, it becomes possible to cause the spring means to generate the auxiliary driving
force in a state where the auxiliary driving force by the spring means is required
(for example, a state where a driving force which should act on the specific joint
is relatively large and the spring means can generate the auxiliary driving force
in the same direction to the driving force). It also becomes possible to prevent
the spring means from generating the auxiliary driving force in a state other than
the above.
Hence, according to the present invention, a burden on the joint actuator
can be reduced when necessary. As a result, it becomes possible to allow the legged
mobile robot to move with various kinds of gaits while using a relatively small
joint actuator. In addition, due to the relative displacement motion of the pair
of link members, the spring means stores the elastic energy which generates the
auxiliary driving force. Thus, it becomes possible that the auxiliary driving force
is generated while effectively utilizing kinetic energy of the robot. As a result,
utilization efficiency of the entire energy of the robot can be improved.
Note that, in a biped mobile robot having two legs like a human, it is preferred
that the specific joint be a knee joint.
In the invention described above, it is preferred that the control means control
the motion transmission continuation/discontinuation means to discontinue transmission
of a bending and stretching motion of the pair of link members to the spring means
at least during a first predetermined period in a state where each of the legs
is lifted off a floor. In general, the driving force to be generated at each of
the joints of each of the legs is relatively small in the state where the each
of the legs is lifted off the floor (a state of free leg period of each of the
legs). If the auxiliary driving force by the spring means is generated in such
a state, the auxiliary driving force becomes larger than the driving force originally
required for the specific joint. This is likely to result in a situation where
a further excessive driving force must be generated to the joint actuator of the
specific joint, in order to reduce the auxiliary driving force. Therefore, in the
present invention, transmission of the relative displacement motion to the spring
means is discontinued at least during the first predetermined period in the state
where each of the legs is lifted off the floor, so that the auxiliary driving force
by the spring means is not generated. Thus, the excessive driving force is not
generated in the joint actuator, thereby reducing energy consumed by the joint
actuator. Further, the auxiliary driving force by the spring means is not generated
during the first predetermined period in the state where each of the legs is lifted
off the floor. Thus, a posture of each of the legs is not affected by the spring
means, and thereby the state of the posture of each of the legs is stably controlled
to be in a desired state of the posture.
Moreover, in the present invention, preferably, while the legged mobile
robot is moving with a predetermined gait which has been decided in advance, the
control means controls the motion transmission continuation/discontinuation means
to continue transmission of the bending and stretching motion of the pair of link
members to the spring means at least during a second predetermined period in a
state where each of the legs lands on the floor. Specifically, the auxiliary driving
force by the spring means is not necessarily always generated in the state where
each of the legs lands on the floor while the legged mobile robot is moving. Basically,
it is preferred that the auxiliary driving force be generated under a situation
where the driving force to be generated to the specific joint of each of the legs
becomes relatively large. Therefore, the relative displacement motion is transmitted
to the spring means at least during the second predetermined period in the state
where each of the legs lands on the floor, while the robot is moving with the predetermined
gait. Thus, the auxiliary driving force can be generated by the spring means only
in the situation where the auxiliary driving force is required.
In this case, it is preferred that the second predetermined period in the state
where each of the legs lands on the floor be determined such that relative displacement
amounts between the pair of link members at start time and stop time of the second
predetermined period are approximately the same. Specifically, if the relative
displacement amounts at the start time and the stop time of the second predetermined
period are largely different from each other, the spring means cannot entirely
release the elastic energy at the stop time of the second predetermined period.
Therefore, since the auxiliary driving force of the spring means is not sufficiently
small yet, the auxiliary driving force to be acted on the specific joint by the
spring means becomes discontinuous at the stop time of the second predetermined
period. In the case like this, an inappropriate variation of the behavior (a non-smooth
change in the behavior) of each leg of the robot occurs easily. Additionally, free
vibration occurs from the stop time of the second predetermined period, especially
when the spring means is a solid spring such as a coiled spring. Thus, when starting
transmission of the relative displacement motion of the pair of link members to
the spring means thereafter, the auxiliary driving force which is acted on the
specific joint by the spring means is discontinuously changed and the like. Therefore,
the auxiliary driving force may become inappropriate. Hence, in the present invention,
the second predetermined period is determined such that the relative displacement
amounts between the pair of link members at the start time and stop time of the
second predetermined period become approximately the same. Accordingly, the spring
means is in the state where the elastic energy is released (a state where the auxiliary
driving force of the spring means is about "0") at the stop time of the second
predetermined period during which the auxiliary driving force by the spring means
is generated. Therefore, it is possible to avoid a situation where the auxiliary
driving force to be acted on the specific joint by the spring means discontinuously
changes at the stop time of the second predetermined period at which transmission
of the relative displacement motion to the spring means stops. It is also possible
to avoid a situation where free vibration occurs from the stop time of the second
predetermined period. Consequently, the legs of the robot can be actuated with
smooth behavior.
In the present invention in which the auxiliary driving force by the spring means
is generated in the state where each of the legs lands on the floor while the robot
is moving with the predetermined gait as mentioned above, it is preferable that
means for controlling a driving force of the joint actuator is provided such that,
while the motion transmission continuation/discontinuation means is continuing
transmission of the relative displacement motion of the pair of link members to
the spring means, a sum of the auxiliary driving force by the spring means and
the driving force of the joint actuator becomes a desired driving force determined
to follow a desired gait of the legged mobile robot.
According to the above, the total driving force acting on the specific
joint is controlled to be the desired driving force determined to follow the desired
gait of the robot (a required value of the driving force which should be generated
to the specific joint to allow the gait of the robot to follow the desired gait)
regardless of whether the auxiliary driving force by the spring means is being
generated. Thus, the operation of the robot can be performed smoothly.
Moreover, the means for controlling the driving force of the joint actuator
as mentioned above estimates the auxiliary driving force by the spring means based
on a variation of the relative displacement amount between the pair of link members
from the start time of the second predetermined period and characteristic data
of the auxiliary driving force of the spring means, which is obtained in advance.
Specifically, the auxiliary driving force changes depending on the
variation of the relative displacement amount between the pair of link members
from the start time of the second predetermined period. In addition, the form of
the variation depends on the characteristics of the spring means. Therefore, by
estimating the auxiliary driving force by the spring means in the above-mentioned
manner, an appropriate estimated value of the auxiliary driving force can be obtained.
Consequently, the driving force of the joint actuator can be appropriately controlled.
Note that the auxiliary driving force by the spring means can be detected directly
by the use of a force sensor or the like.
Moreover, in the present invention, the spring means may be a solid spring
such as a coiled spring, a leaf spring, a torsion spring, a metal spring, rubber
and the like, as a matter of course. However, it is preferred that the spring means
be a gas spring which elastically generates the auxiliary driving force by compression
and expansion of gas. Specifically, the gas spring unlikely to cause free vibration
in comparison with the solid spring. Therefore, free vibration of the spring means
can be prevented especially when transmission of the relative displacement motion
to the spring motion is discontinued. Thus, when the transmission of the relative
displacement motion to the spring means is re-started after transmission thereof
has been discontinued, the desired auxiliary driving force of the spring means
can be generated smoothly.
Moreover, in the present invention, it is preferred that the joint actuator
be an electric motor. Specifically, in the present invention, the burden on the
joint actuator of the specific joint can be reduced as described earlier. Therefore,
a current flowing through the electric motor serving as the joint actuator can
be small, and an energy loss due to Joule heat or the like can be minimized. In
addition, the use of the electric motor as the joint actuator can realize smooth
motion control of the legs of the robot. Furthermore, a vibration component of
the motion of the legs caused by the spring means can be easily diminished by control
of the electric motor, without providing a mechanical buffering device (damping
device), especially in a state of generating the auxiliary driving force by the
spring means. Thus, stable control of the motion of the robot can be smoothly performed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an explanatory view showing the entire structure of a legged mobile
robot in a first embodiment of the present invention;
FIGS. 2(
a) and 2(
b) are explanatory views exemplifying
spring means of an assist device provided in the robot in FIG. 1;
FIGS. 3(
a) and 3(
b) are cross sectional views showing
a configuration of an essential part of the assist device provided in the robot
in FIG. 1;
FIG. 4 is a diagram showing characteristics of the spring means provided in
the robot in FIG. 1; and
FIG. 5 is a block diagram showing a functional configuration of a control unit
provided in the robot in FIG. 1.
FIG. 6 is a flowchart showing processing by the control unit provided in the
robot in FIG. 1;
FIG. 7 is a flowchart showing subroutine processing of an essential part of
the flowchart in FIG. 6; and
FIG. 8 is a diagram for explaining actuation of the assist device provided in
the robot in FIG. 1.
FIG. 9 is a diagram for explaining actuation of an assist device in a second
embodiment of the present invention;
FIGS. 10(
a) and 10(
b) are cross sectional views showing
a configuration of an essential part of an assist device in a third embodiment
of the present invention;
FIG. 11 is a diagram showing characteristics of spring means provided in the
assist device in FIG. 10;
FIGS. 12(
a) and 12(
b) are cross sectional views showing
a configuration of an essential part of an assist device in a fourth embodiment
of the present invention; and
FIG. 13 is an explanatory view showing a configuration of an assist device in
a fifth embodiment of the present invention.
FIG. 14 is an explanatory view showing a configuration of an assist device in
a sixth embodiment of the present invention;
FIG. 15 is a cross sectional view showing a configuration of an essential part
of the assist device in FIG. 14;
FIG. 16 is an explanatory view showing a configuration of an assist device in
a seventh embodiment of the present invention;
FIG. 17 is a cross sectional view showing a configuration of an essential part
of the assist device in FIG. 16;
FIG. 18 is an explanatory view showing a configuration of an assist device in
an eighth embodiment of the present invention;
FIG. 19 is a cross sectional view showing a configuration of an essential part
of the assist device in FIG. 18;
FIG. 20 is an explanatory view showing a configuration of an assist device in
a ninth embodiment of the present invention; and
FIG. 21 is an explanatory view showing a configuration of an assist device in
a tenth embodiment of the present invention.
FIG. 22 is an explanatory view showing a configuration of an assist device in
an eleventh embodiment of the present invention;
FIG. 23 is a diagram showing characteristics of spring means provided in the
assist device in FIG. 22;
FIG. 24 is a diagram showing characteristics of spring means related to a modified
aspect of the eleventh embodiment;
FIG. 25 is an explanatory view showing a configuration of an assist device in
a twelfth embodiment of the present invention;
FIG. 26 is an explanatory view showing a configuration of an assist device in
a thirteenth embodiment of the present invention; and
FIG. 27 is a cross sectional view showing a configuration of an essential part
of the assist device in FIG. 26.
BEST MODE FOR CARRYING OUT THE INVENTION
A first embodiment of the present invention is described with reference to FIGS.
1 to 8. FIG. 1 is a schematic view depicting a configuration of a biped mobile
robot as the legged mobile robot of this embodiment. As illustrated, the robot
1 is provided with two legs
3 and
3 extending downward from
a body
2. Note that these legs
3 and
3 have the same structure
and thus one of the legs
3 (the forward-left leg
3 of the robot
1
in the figure) is shown only partially.
Similarly to the leg of a human, each of the legs
3 is configured
by sequentially connecting a thigh portion
4, a crus portion
5, and
a foot portion
6 through a hip joint
7, a knee joint
8, and
an ankle joint
9, respectively, from the body
2. To be more specific,
the thigh portion
4 of each of the legs
3 extends from the body
2
through the hip joint
7, the crus portion
5 is connected to the thigh
portion
4 through the knee joint
8, and the foot portion
6
is connected to the crus portion
5 through the ankle joint
9. Note
that respective ones of the thigh portion
4, the crus portion
5 and
the foot portion
6 correspond to link members in this invention.
In this case, the hip joint
7 is enabled to have rotational motions about
three axes in directions of front and back, right and left, and top and bottom
of the robot
1. The knee joint
8 is enabled to have a rotational
motion about one axis in the right and left direction. The ankle joint
9
is enabled to have rotational motions about two axes in the directions of front
and back, and the right and left. Because of the rotation motions of each of the
joints
7,
8 and
9, each of the legs
3 can have a motion
which is almost the same as that of the leg of the human. In addition, the knee
joint
8, for example, is provided with an electric motor
10 (hereinafter,
referred to as a knee joint electric motor
10) as a joint actuator in order
to perform the rotational motion about one axis in the right and left direction.
Further, although not illustrated, the hip joint
8 is provided with three
electric motors for performing the rotational motions about the three axes, respectively.
The ankle joint
9 is provided with two electric motors for performing the
rotational motions about two axes, respectively.
Note that, in this embodiment, each of the foot portions
6 is connected
to the ankle joint
9 through a six-axis force sensor
11 in order
to detect a floor reaction force (translational forces in three-axis directions
of front and back, right and left, and top and bottom of the robot
1 and
moments about the three axes) acting on each of the foot portions
6. Moreover,
each of the joints
7,
8 and
9 is provided with an encoder
(not shown) for detecting a rotation position thereof (specifically, a rotation
angle of the electric motor of each of the joints
7 to
9).
In this embodiment, the knee joint
8 of each of the legs
3 is a
specific joint in this invention, and an assist device
12 for applying an
auxiliary driving force to the knee joint
8 as necessary is provided in
each of the legs
3.
The assist device
12 is provided with a rod member
14 connected
to the crus portion
5 through a free joint
13, a rod member
16
connected to the rod member
14 through spring means
15, and a rod
insertion member
17 through which the rod member
16 is inserted to
be movable in an axis direction thereof. The rod member
14, the spring means
15, the rod member
16 and the rod insertion member
17 as a
whole extend upward almost along the thigh portion
4 from the free joint
13 of the crus portion
5. The circumference portion of the rod insertion
member
17 is connected to the thigh portion
4 through a free joint
18.
Here, the spring means
15 is enabled to store elastic energy. For example,
a solid spring which generates an elastic force by elastic deformation thereof
or a gas spring which generates an elastic force by compression and expansion of
gas such as air can be used as the spring means
15. The solid spring includes
a coiled spring, a leaf spring, a torsion spring, rubber and the like. The gas
spring includes a bag made of rubber or the like in which a gas such as air is
sealed, a cylinder with a piston where the gas is sealed and the like. Further,
the spring means
15 is connected to the rod members
14 and
16
so as to generate an elastic force corresponding to a change of spacing between
these rod members
14 and
16.
To be more specific, when, for example, a coiled spring which is a solid spring
is used as the spring means
15, both ends of a coiled spring
19 are
joined to the rod members
14 and
16, respectively, as shown in FIG.
2(
a). Alternatively, when, for example, a gas spring having a cylinder configuration
is used as the spring means
15, the rod member
14 is joined to a
cylinder
20 and the rod member
16 is joined to a piston
21
as shown in FIG. 2(
b). The piston
21 is slidable within the cylinder
20 in an axis direction thereof. Gas such as air is then sealed within gas
chambers
22 and
23 formed within the cylinder
20 above and
below the piston
21. Note that, in this case, the rod members
14
and
16 may be joined to the piston
21 and the cylinder
20,
respectively, in reverse to the above. In addition, one of the gas chambers
22
and
23 within the cylinder
20 may be opened to, for example, the atmosphere.
Note that, in the description below, a state where the spring means
15
has released the elastic energy thereof (state where no elastic force is generated)
is referred to as a natural length state of the spring means
15 as a matter
of convenience.
As further shown in FIGS. 3(
a) and
3(
b), the foregoing assist
device
12 is provided with a lock mechanism
24 which latches the
rod member
16 so that the rod member
16 cannot move relative to the
rod insertion member
17. This lock mechanism
24 corresponds to motion
transmission continuation/discontinuation means in this invention and has the following
configuration. In one side portion of the rod member
16, a plurality of
recesses
16a are provided at intervals in the longitudinal direction
thereof (a movable direction of the rod member
16). Further, the rod insertion
member
17 is provided with a latch pin
25 to be able to move forward
and backward to the side portion of the rod member
16 having the above-mentioned
recesses
16a. By the forward and backward movement, the latch pin
25 can be fitted into each of the recesses
16a of the rod
member
16 as shown FIG. 3(
b). In this case, the latch pin
25
is moved forward and backward by energization control of, for example, an electromagnetic
solenoid
26. By fitting the latch pin
25 into the recess
16a,
the lock mechanism
24 latches the rod member
16 so that the rod member
16 cannot move relative to the rod insertion member
17.
With the above-mentioned configurations of the assist device
12 and the
lock mechanism
24, in the state where the latch pin
25 of the lock
mechanism
24 is moved backward (state of FIG. 3(
a)), the rod member
16 can be freely moved integrally with the spring member
15 and the
rod member
14 in the axis direction of the rod member
16 (hereinafter,
the above state is referred to as a free state) in synchronization with a bending
and stretching motion of the thigh portion
4 and the crus portion
5
at the knee joint
8 (this motion corresponds to a relative displacement
motion in this invention and hereinafter referred to as a knee bending and stretching
motion). In this free state, the knee bending and stretching motion is not transmitted
to the spring means
15, and the spring means
15 is kept in an almost
natural length state. Therefore, in the free state, an elastic force is not applied
to the knee joint
8 of the leg
3 from the spring means
15.
Alternatively, when the latch pin
25 is moved forward during
the knee bending and stretching motion so that the latch pin
25 is fitted
into one of the recesses
16a of the rod member
16, the rod
member
16 is latched so as not to be moved relative to the rod insertion
member
17 from when the latch pin
25 is inserted (hereinafter, this
state is referred to as a locked state). In this locked state, the spring means
15 is compressed or extended from the natural length state by the knee bending
and stretching motion. The spring means
15 then stores elastic energy and
generates an elastic force. Thereafter, the elastic force acts on the knee joint
8 as a rotation force (auxiliary driving force) of the knee joint
8
in parallel with a rotation force of the knee joint
8 by the foregoing knee
joint electric motor
10. In this case, the rotation force of the knee joint
8 by the spring means
15 (hereinafter, referred to as an auxiliary
knee rotation force) depends on a variation of a bending angle θ between
the thigh portion
4 and the crus portion
5 (hereinafter, referred
to as a knee bending angle θ; see FIG. 1) from a knee bending angle at start
time of the locked state (transition from the free state to the locked state) (hereinafter,
referred to as a lock start knee bending angle).
More specifically, referring to FIG. 4, if the lock start knee bending angle
is "θ
1," the auxiliary knee rotation force by the spring means
15
changes relative to the knee bending angle θ with, for example, characteristics
shown by a solid line a in FIG. 4. Further, if the lock start knee bending angle
is "θ
2" (θ
1>θ
2), the auxiliary knee
rotation force by the spring means
15 changes relative to the knee bending
angle θ with characteristics shown by a solid line b in FIG. 4. Here, the
knee bending angle θ in this embodiment is an inclination angle of the axis
of the crus portion
5 with reference to the axis of the thigh portion
4
as shown in FIG. 1. The more the leg
3 bends at the knee joint
8,
the larger the knee bending angle θ becomes. Moreover, the auxiliary knee
rotation force by the spring means
15 at the knee joint
8 in a bending
direction of the leg
3 is expressed by a positive value, and the same in
a stretching direction of the leg
3 is expressed by a negative value. Therefore,
when the knee bending angle θ is decreased from the foregoing lock start
knee bending angle (in a motion in the stretching direction of the leg
3),
the auxiliary knee rotation force by the spring means
15 increases in the
bending direction of the leg
3. When the knee bending angle θ is increased
from the lock start knee bending angle (in a motion in the bending direction of
the leg
3), the auxiliary knee rotation force by the spring means
15
increases in the stretching direction of the leg
3. Furthermore, the smaller
the lock start knee bending angle is, the larger the auxiliary knee rotation force
at each of the knee bending angles θ becomes in the stretching direction
of the leg
3. In addition, the auxiliary knee rotation force by the spring
means
15 at the lock start knee bending angle is almost "0."
Note that the characteristics of the change of the auxiliary knee rotation force
(curves of the solid lines a and b in FIG. 4) relative to the change of the knee
bending angle θ are uniform at any lock start knee bending angle. Moreover,
in the foregoing free state, the spring means
15 is in the natural length
state as mentioned earlier. Thus, the auxiliary knee rotation force by the spring
means
15 is almost "0" at any knee bending angle θ. Furthermore, in
this embodiment, the aforementioned knee bending angle θ corresponds to a
relative displacement amount between the thigh portion
4 and the crus portion
5 as a pair of link members.
Referring back to FIG. 1, mounted within the body
2 of the robot
1 are: a control unit
27 which performs, for example, operation control
of the respective joints
7,
8 and
9 of each of the legs
3;
a storage device
28 as a power source of the electric motors of the respective
joints
7,
8 and
9, and the like; an inclination sensor
29
which detects an inclination angle of the body
2; a motor driver circuit
30 for controlling energizing of the respective electric motors; and the
like. Note that the inclination sensor
29 is configured by using a gyro
sensor, an accelerometer or the like. Moreover, the storage device
28 is
configured by a battery (secondary battery), a condenser or the like.
The control unit
27 is configured by electronic circuits including a microcomputer
and the like. As shown in FIG. 5, the control unit
27 is provided with a
gait generator
31, a motor controller
32, and a lock mechanism controller
33 as functional constituents thereof.
In each step (every time a supporting leg changes) while the robot
1 is
moving, the gait generator
31 decides gait parameters (length of step, walking
cycle, motion mode and the like) which define desired gaits of both legs
3
and
3 of the robot
1 (desired forms of the motions of both legs
3
and
3), corresponding to a command from the outside, teaching data (data
for a planned movement) which has been already set, or the like. Further, based
on the gait parameters, the gait generator
31 generates a desired gait (a
desired instantaneous gait) for each predetermined control cycle. Here, the gait
parameters generated by the gait generator
31 in this embodiment are parameters
which define the desired gaits and the like for permitting the robot
1 to
perform a normal walking motion and the same for permitting the robot
1
to perform a running motion similar to a human running motion. The desired gait
includes, for example: desired values of position and posture of the body
2
of the robot
1 (hereinafter, referred to as desired body position/posture);
desired values of position and posture of each of the foot potions
6 of
the robot
1 (hereinafter, referred to as desired foot position/posture);
a desired value of a resultant force (total floor reaction force) of floor reaction
forces (translation forces and moment) acting on the respective foot portions
6
and
6 (hereinafter, referred to as desired total floor reaction force);
and a desired position of so-called ZMP (Zero Moment Point) (hereinafter, referred
to as a desired ZMP) as a point of action of the total floor reaction force. Note
that further details of constituents of the aforementioned desired gait are provided
by the applicant of the application concerned, in Japanese Patent Laid-Open Publication
No. Heisei 11-300660, for example. Thus, detailed description thereof is omitted
herein. Moreover, the content of the desired gait is not limited to that disclosed
in the abovementioned publication, as long as it expresses a desired form of the
motion of the robot
1.
The lock mechanism controller
33 has a function to control the lock mechanism
24 of the foregoing assist device
12 to be in the aforementioned
locked state or the free state. Corresponding to the desired gait (to be more specific,
the gait parameters defining the desired gait) generated by the gait generator
31, this lock mechanism controller
33 decides a period during which
the lock mechanism
24 is in the locked state (this state corresponds to
a second predetermined period in this invention, and hereinafter referred to as
a lock period) or a period during which the lock mechanism
24 is in the
free state (this state corresponds to a first predetermined period in this invention,
and hereinafter referred to as a free period) as described later. During the decided
lock period, the lock mechanism controller
33 outputs a lock command to
the lock mechanism
24 in order to direct the lock mechanism
24 to
the locked state. Alternatively, in the decided free period (a period except the
lock period), the lock mechanism controller
33 outputs a free command to
the lock mechanism
24 in order to direct the lock mechanism
24 to
the free state. Here, in this embodiment, the lock mechanism
24 is actuated
by moving the latch pin
25 forward and backward by the use of the electromagnetic
solenoid
26 as described earlier. Therefore, to be more specific, the abovementioned
lock command and the free command are commands for energization control of the
aforementioned electromagnetic solenoid
26 of the lock mechanism
24.
Note that the lock mechanism controller
33 corresponds to control means
in this invention.
The motor controller
32 sequentially controls the electric motors of the
respective joints
7,
8 and
9, including the foregoing knee
joint electric motor
10 (specifically, sequentially controls rotation angles
of the electric motors). As described later, this motor controller
32 sequentially
generates torque commands (specifically, command values of the current to energize
the electric motors) which define torque to be generated in the respective electric
motors, based on the desired gait generated by the gait generator
31, an
actual inclination angle of the body
2 detected by the foregoing inclination
sensor
29, actual rotation angles of the respective joints
7,
8
and
9 of the leg
3 detected by using the unillustrated encoders,
an actual floor reaction force of each of the foot portions
6 detected by
the foregoing six-axis force sensor
11, data of the foregoing lock period
(or the free period) decided by the foregoing lock mechanism controller
33,
and the like. Thereafter, the motor controller
32 outputs the generated
torque commands to the motor driver circuit
30, causing the respective electric
motors to generate torque in accordance with the torque commands, through the motor
driver circuit
30.
Next, actuation of a system of this embodiment is described. The aforementioned
control unit
27 performs a predetermined initialization processing such
as initialization of a timer and the like, and thereafter executes processing of
the flowchart in FIG. 6 for each predetermined control cycle (for example, 50 ms)
which is set in advance. Specifically, the control unit
27 first determines
whether it is a switch moment of the gait of the robot
1 (STEP
1).
To be more specific, the switch moment of the gait is the instance of the supporting
leg, one of the legs
3, switching to the other leg
3, while the robot
1 is moving. When the switch moment of the gait does not exist in STEP
1,
the processing of the control unit
27 proceeds to a processing in STEP
3
which will be described later.
When it is a switching moment of the gait, in STEP
1, the control unit
27 causes the foregoing gait generator
31 to generate (renew) the
gait parameters which define the desired gait of the robot
1, based on a
motion command of the robot
1 given from the outside or the data for a planned
movement set in advance (STEP
2). Here, the desired gait defined by the
gait parameters generated by the gait generator
31 is a desired gait used
until the next switch moment in the gait or the moment slightly after the next
switch moment in the gait. Additionally, in this case, the desired gait defined
by the gait parameters generated by the gait generator
31 is a desired gait
of a running motion of the robot
1 (for example, a desired gait with which
the robot
1 performs motions of the legs
3 and
3 with steps
similar to those of a running human), in a case where the motion command, indicating
that the robot
1 should perform a running motion, is given from the outside,
or in a situation where the robot
1 should perform a running motion according
to the data for a planned movement of the robot
1.
Next, the control unit
27 executes processings of STEPS
3 to
5 by use of the motor controller
32. The processings of STEPS
3
to
5 are for obtaining torque commands (hereinafter, referred to as basic
torque commands) to the electric motors of the respective joints
7,
8
and
9, when the lock mechanism
24 of the assist device
12
is in the free state (where the auxiliary knee rotation force by the spring means
15 does not act on the knee joint
8). These torque commands are required
in order to direct the motion of the robot
1 to follow the aforementioned
desired gait. Note that the processings of STEP
3 to
5 have already
been detailed by the applicant of the application concerned in Japanese Patent
Laid-Open Publication No. Heisei 11-300660. Therefore, brief outlines of the processings
of STEP
3 to
5 are provided in the following.
In STEP
3, the control unit
27 obtains a desired instantaneous
gait
based on the gait parameters currently generated by the gait generator
31.
The desired instantaneous gait is the desired gait for each control cycle of processing
of the control unit
27. To be more specific, the desired instantaneous gait
includes the desired body position/posture, the desired foot position/posture,
the desired total floor reaction force, and the desired ZMP, for each control cycle,
as mentioned earlier. Note that, in the processing of STEP
3, a desired
floor reaction force of each of the legs
3 for each control cycle as well
as a point of action of the desired floor reaction force of the same are further
obtained, based on the above-mentioned desired foot position/posture, the desired
total floor reaction force, the desired ZMP and the like.
In STEP
4, the control unit
27 corrects the desired foot position/posture
of the above-mentioned desired instantaneous gait by a composite-compliance operation
processing. To be more specific, in this composite-compliance operation processing,
obtained is a floor reaction force (moment) to be acted on the robot
1 in
order to restore the actual inclination angle of the body
2 of the robot
1 (detected by the foregoing inclination sensor
29) to a desired
inclination angle set by the aforementioned desired body position/posture (cause
the deviation between the actual inclination angle and the desired inclination
angle to be "0"). Thereafter, a resultant force of this floor reaction force (moment)
and the aforementioned desired total floor reaction force is set as a desired value
of the entire floor reaction force to be actually acted on the robot
1.
Subsequently, the desired foot position/posture for each control cycle is corrected
so that a resultant force of the actual floor reaction force of each of the foot
portions
6, detected by the six-axis sensor
11 of each of the legs
3, follows the desired value. This kind of composite-compliance operation
processing is for ensuring autonomous stability of the posture of the robot
1.
In STEP
5, the control unit
27 obtains the basic torque commands
to the respective electric motors of the joints
7,
8 and
9
of each of the legs
3 of the robot
1. To be more specific, in this
processing, desired rotation angles of the respective joints
7,
8
and
9 of each of the legs
3 of the robot
1 are obtained by
an inverse kinematics calculation processing based on a model of the robot
1
(a rigid body link model), using the desired body position/posture in the desired
instantaneous gait, the desired foot position/posture corrected in STEP
4
as mentioned above, and the like. Thereafter, the torque commands to the electric
motors of the respective joints
7,
8 and
9 are obtained so
that actual rotation angles of the respective joints
7,
8 and
9
(detected by the unillustrated encoder provided in each of the joints
7,
8 and
9) follow these-desired rotation angles.
In this case, for example, the torque command for the knee joint electric motor
10 of each of the legs
3 is obtained by the following equation (1)
using a deviation Δθ between the desired rotation angle of the knee
joint
8 (desired value of the knee bending angle θ) and an actual
rotation angle of the knee joint
8 (detected value of the knee bending angle
θ), and torque Tff of the electric motor
10 (hereinafter, referred
to as a reference torque Tff) required to generate the aforementioned desired floor
reaction force to the leg
3.
Note that the reference torque Tff used for the calculation of the equation
(1) is obtained by the inverse kinematics calculation processing (inverse dynamics
calculation processing) based on a model of the robot
1, using the desired
body position/posture, the desired foot position/posture, the desired floor reaction
force to the leg
3, desired rotation angle acceleration of each of the joints
7,
8 and
9, and the like. Further, factors Kp and Kv of the
equation (1) are gain coefficients set in advance. A factor dΔθ/dt
is the time derivative of the deviation Δθ.
Here, the first and second terms on the right hand side of the equation (1)
are feedback control terms corresponding to the deviation Δθ. The third
term on the right hand side thereof is a feed-forward control term for compensating
an influence of the floor reaction force acting on the leg
3. The second
term on the right hand side in particular is a term having a buffer function (damping
function) which swiftly diminishes vibration relative to the desired value of the
knee bending angle θ.
The basic torque commands for the electric motors of the joints
7 and
9 other than the knee joint
8 are obtained in a similar manner to
the above. As described earlier, the basic torque commands obtained in this manner
are torque commands to the electric motors of the respective joints
7,
8
and
9, required to cause the motion of the robot
1 to follow the
foregoing desired gait in a state where the auxiliary knee joint rotation force
by the spring means
15 of the assist device
12 is not acting on the
knee joint
8.
Next, in STEP
6, the control unit
27 causes the foregoing lock
mechanism controller
33 to execute a processing for controlling the lock
mechanism
24 of the assist device
12. This processing is performed
as shown in the flowchart in FIG. 7. Specifically, the lock mechanism controller
33 first sets the lock period during which the lock mechanism
24
is in the locked state, based on the gait parameters currently set by the gait
generator
31 (STEP
6-
1). In this case, in the present embodiment,
when the gait parameters are those which cause the robot
1 to perform, for
example, a normal walking motion, the lock mechanism controller
33 directs
the lock mechanism
24 to the free state (does not allow the auxiliary knee
rotation force by the spring means
15 to act on the knee joint
8)
over the entire period of the walking motion. Hence, the lock period is not set
in this case.
On the other hand, when the gait parameters are those which cause the robot
1
to perform, for example, a running motion (running motion similar to that o
