JP2008044066A - Legged robot - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a legged robot which can reduce a torque to be output from motors of the coxae arranged on a pitching axis in walking. <P>SOLUTION: The legged robot 100 comprises a trunk link 10, and leg portions 30, 50. The respective leg portions have a rotary axis C1 extending toward the sides of the trunk, and are connected to the trunk link 10 by means of the coxae 32, 52 having motors therein. Springs 20 are arranged between the trunk link 10 and the respective leg portions. The springs 20 are arranged such that the relative angle between the trunk link and the leg portions in the natural length of the springs is within the range between the relative angle when the leg portions have swung to the frontmost position with respect to the trunk link in walking and the relative angle when the leg portions have swung to the rearmost position with respect to the trunk link in walking. The elastic forces caused by the elongation and contraction of the springs operate so as to assist the motors of the coxae 32, 52 in both of the accelerating period at the start of the swing of the leg portions in walking and the decelerating period at the finish of the swing. As a result, the torque to be output from the motors of the coxae arranged on the pitching axis in walking can be effectively reduced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a legged robot that has a leg portion that is swingably connected to a trunk link and walks by swinging the leg portion around a rotation axis that extends in a body side direction by a motor. In this specification, the legged robot may be simply referred to as a robot.

A legged robot having a plurality of legs walks while swinging the legs back and forth around a rotation axis extending in the body side direction. The number of legs is typically two or four, but may be any number as long as there are a plurality of legs.
The leg portion includes a plurality of links and a joint that connects adjacent links so as to be swingable. The trunk link and one link of the leg are also slidably connected by a joint. Each joint is provided with a motor that changes the relative angle between the links connected to the joint. As each motor outputs an appropriate driving force and controls the relative angle between the links, the legged robot walks with its entire leg swinging back and forth with respect to the trunk link. The motor referred to in this specification is a device that converts energy such as steam, electricity, gasoline, etc. into mechanical motion and transmits it, and typically means an electric motor or an engine.
In order to reduce energy consumption, it is preferable that the legged robot can use a small and low output motor. Therefore, legged robots that utilize the elastic force of an elastic body such as a spring to assist the driving force of the motor have been studied. For example, Patent Document 1 and Patent Document 2 propose a legged robot that interposes an elastic member between links connected to a joint and assists the driving force of the joint motor by the elastic force generated by the elastic member. ing. In the present specification, “assisting the driving force of the joint motor” may be expressed as “assisting the joint motor”.

  The legged robot disclosed in Patent Literature 1 and Patent Literature 2 includes an elastic member that connects one end to a thigh link and the other end to a lower leg link. The elastic member generates an elastic force corresponding to the relative angle of the thigh link and the lower leg link around the knee joint, that is, the degree of bending of the knee joint. The elastic force generated by the elastic member applies torque around the rotation axis of the knee joint to the thigh link and the crus link. The direction of the torque is a direction to cancel the knee joint bending. Therefore, the elastic force generated by the elastic member acts to assist the motor of the knee joint that controls the relative angle between the thigh link and the lower leg link around the knee joint.

JP 2003-103480 A JP 2003-145477 A

The techniques of Patent Document 1 and Patent Document 2 focus on a knee joint motor that requires a large driving force to support a trunk link against gravity. The techniques of Patent Document 1 and Patent Document 2 are techniques for assisting the motor of the knee joint by the elastic force generated according to the degree of bending of the knee joint by the elastic member interposed between the thigh link and the lower leg link. .
Motors that require a large driving force are not limited to knee joint motors. According to the inventor's study, it has been found that when the legged robot walks, a large driving force is also required for the motor of the hip joint that swings the leg portion back and forth with respect to the trunk link. Therefore, a technique for assisting a hip joint motor for swinging the leg portion back and forth with respect to the trunk link during walking is desired.
If an elastic member is interposed between the trunk link and the leg, an elastic force corresponding to the relative angle around the rotation axis extending in the body side direction of the trunk link and the leg is applied to the leg around the rotation axis. Is possible. However, the elastic member has a natural length at which the generated elastic force is zero. When the elastic member is shorter than the natural length, the elastic member generates an elastic force in the extending direction, and when the elastic member is longer than the natural length, an elastic force in the shortening direction is generated. That is, the direction of the elastic force generated by the length of the elastic member is reversed. It is necessary to avoid that the elastic force acts only in the direction of assisting the motor and the elastic force acts in a direction in which a load is further applied to the motor. Therefore, in patent document 1, the means to release the connection of an elastic member and a link is provided. When the relative angle between the thigh link and the lower leg link is within a predetermined range, the connection between the elastic member and the link is released. By doing so, it is avoided that the elastic force which an elastic member generate | occur | produces acts in the direction which gives a load further to a motor.
However, in the technique of Patent Document 1, the motor cannot be assisted while the connection between the elastic member and the link is released. If the characteristics of the elastic member that the direction of the elastic force generated by the length is reversed can be used well, the hip joint motor for swinging the leg part back and forth with respect to the trunk link is effective. It becomes possible to assist. The hip joint referred to in this specification means a joint that connects the trunk link and the leg, and includes, for example, a joint that connects the front leg of the legged robot having four legs and the trunk link. Hereinafter, a hip joint that swings the leg portion back and forth (that is, a hip joint having a rotation axis extending in the body side direction) is referred to as a pitch axis hip joint. A rotation axis extending in the body side direction of the trunk link is referred to as a pitch axis.

  The present invention combines the characteristics of the elastic member that the direction of the elastic force generated by its length is reversed and the characteristic that the legged robot periodically swings the leg part in the front-rear direction during walking. Thus, a technique for effectively assisting the output of the motor of the hip joint for swinging the leg portion back and forth with respect to the trunk link during walking is provided.

The present invention has a trunk link and a leg that is swingably connected to the trunk link, and a leg that swings around a rotation axis that extends in the body side direction by a motor and walks. Can be embodied in a robot. This legged robot has one end connected to the trunk link and the other end connected to the leg, and generates an elastic force according to the relative angle between the trunk link and the leg around the rotation axis. And an elastic member for applying a torque around the rotation axis to the leg portion.
According to the above configuration, the relative angle between the trunk link and the leg when the elastic member has a natural length, the relative angle when the leg swings most forward with respect to the trunk link during walking, and walking Sometimes the leg can be between the relative angles when it swings most backward with respect to the trunk link.

The relative angle between the trunk link and the leg when the elastic member has a natural length is referred to as a neutral relative angle. Also, the relative angle when the leg swings most forward with respect to the trunk link during walking is called the front end relative angle, and the relative angle when the leg swings most backward with respect to the trunk link during walking. The corner is referred to as a rear end relative angle. The relative angle between the trunk link and the leg changes periodically between the front end relative angle and the rear end relative angle during walking. In the legged robot according to the present invention, the neutral relative angle exists between the front end relative angle and the rear end relative angle.
The elastic force generated by the elastic member acts on the leg as torque around the rotation axis. The torque acts in a direction that causes the relative angle of the legs to move toward the neutral relative angle. Therefore, when the leg is located behind the trunk link and the relative angle is between the rear end relative angle and the neutral relative angle, the torque caused by the elastic force accelerates the leg forward. Act on. On the other hand, when the leg is located in front of the trunk link and the relative angle is between the front end relative angle and the neutral relative angle, the torque caused by the elastic force is in the direction of accelerating the leg backward. Works.

On the other hand, the motor of the pitch axis hip joint outputs torque in a direction that accelerates the free leg forward in order to swing forward the free leg that left the floor behind the trunk link. At this time, the pitch axis hip joint motor on the stance leg side outputs torque in a direction to accelerate the stance leg positioned forward of the trunk link to the trunk link in order to push the trunk link forward.
After the free leg is swung forward, in order to decelerate the free leg in preparation for landing, torque is generated in a direction that accelerates the free leg backward (here, “torque in the direction to accelerate backward”) Is the torque in the direction to decelerate the speed toward the front of the swing leg). At this time, in order to decelerate the trunk link moving forward, the motor of the pitch axis hip joint on the stance side accelerates the standing leg located behind the trunk link forward with respect to the trunk link. The torque is output (the “torque accelerating forward” means torque in the direction of decelerating the speed toward the rear with respect to the trunk link of the stance leg), that is, the motor of the pitch axis hip joint is Even if it is a free leg, when the leg is positioned rearward with respect to the trunk link, torque is generated in a direction that accelerates the leg forward, and the leg is positioned forward with respect to the trunk link. Sometimes torque is generated in a direction that accelerates the legs backward.
As described above, when the leg is positioned behind the trunk link and the relative angle is between the rear end relative angle and the neutral relative angle, the torque caused by the elastic force is in the direction of accelerating the leg forward. Generate torque. When the leg is positioned in front of the trunk link, when the relative angle is between the front end relative angle and the neutral relative angle, the torque resulting from the elastic force generates torque in the direction of accelerating the leg backward.
In other words, the legged robot of the present invention determines the direction of the torque output by the motor of the pitch axis hip joint and the direction of the torque caused by the elastic force, regardless of whether the leg is in front of or behind the trunk link. Can be the same. According to the present invention, the torque resulting from the elastic force generated by the elastic member can be applied to assist the motor of the pitch axis hip joint throughout the walking cycle. A legged robot that effectively assists a hip joint motor for swinging the leg back and forth with respect to the trunk link during walking can be realized.

The neutral relative angle is preferably approximately in the middle of the front end relative angle and the rear end relative angle. In other words, the elastic member has a relative angle between the trunk link and the leg when it is a natural length, and a relative angle when the leg swings most forward with respect to the trunk link during walking, It is preferable that the legs are arranged so as to be approximately in the middle between the relative angles when the legs swing most backward with respect to the trunk link during walking.
The motor assist by the elastic member is as follows from the viewpoint of energy. When the leg portion accelerates, the elastic energy accumulated in the elastic member is converted into a part of the kinetic energy of the leg portion. When the leg portion decelerates, a part of the kinetic energy of the leg portion is converted into the elastic member of the elastic member.
By setting the neutral relative angle as described above, the elastic energy accumulated in the elastic member when the relative angle is the front end relative angle and the elastic energy accumulated in the elastic member when the relative angle is the rear end relative angle. Can be made approximately equal. The energy received from the leg by the elastic member can be made equal to the energy applied to the leg. The motor can be assisted by the elastic member more efficiently.

  The elastic coefficient of the elastic member is set so that the natural vibration period of the leg portion around the rotation axis determined by the moment of inertia around the rotation axis of the leg portion and the elastic coefficient substantially matches the walking cycle of the legged robot. It is preferable that By doing so, it is possible to realize the basic movement of the leg swinging around the rotation axis of the pitch axis hip joint during walking by the elastic force of the elastic member. The motor of the pitch axis hip joint only needs to apply a driving force for giving a subtle motion change that cannot be realized by an elastic force or a driving force for supplying energy dissipated by a damping element of the leg to the leg. It is possible to assist the pitch axis hip joint motor of the legged robot more effectively.

  According to the present invention, it is possible to realize a legged robot that effectively assists the driving force of the motor of the pitch axis hip joint during walking by adding an elastic member.

A legged robot according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic side view of a legged robot 100 according to the present embodiment. The legged robot 100 includes a trunk link 10, a right leg 30, and a left leg 50.
The XYZ coordinate system fixed to the trunk link 10 is referred to as a trunk fixed coordinate system. The X axis of the trunk fixed coordinate system extends forward of the trunk link 10, the Y axis extends in the body side direction of the trunk link 10, and the Z axis extends upward of the trunk link 10. The X axis may be referred to as a roll axis, the Y axis as a pitch axis, and the Z axis as a yaw axis.

The right leg 30 will be described. The right leg 30 includes a right thigh link 38, a right lower leg link 40, and a right foot link 42. The right leg 30 includes a right hip joint 32, a right knee joint 34, and a right ankle joint 36.
One end of the trunk link 10 and the right thigh link 38 is connected to the right hip joint 32. The right knee joint 34 is connected to the other end of the right thigh link 38 and one end of the right lower leg link 40. The right ankle joint 36 is connected to the other end of the right leg link 40 and one end of the right foot link 42.
A motor (not shown) is built in each joint, and the relative angle between the links connected to the joint can be changed by the motor outputting torque.
The right hip joint 32 has a rotation axis C1 extending in the pitch axis direction, and can change the relative angle of the trunk link 10 and the right thigh link 38 around the rotation axis C1.
The relative angle θ around the rotation axis C1 of the trunk link 10 and the right thigh link 38 is represented by an angle formed by the Z axis of the trunk fixed coordinate system and a straight line L extending along the longitudinal direction of the thigh link 38. When the Z axis of the coordinate system fixed to the trunk link 10 and the straight line L along the longitudinal direction of the thigh link 38 overlap when observed from the pitch axis direction, the relative angle θ is set to zero degrees.
When the relative angle θ changes, the overall relative angle of the right leg 30 with respect to the trunk link 10 changes, so the relative angle θ is expressed as a relative angle around the pitch axis of the right leg 30 with respect to the trunk link 10. be able to.
The right knee joint 34 has a rotation axis C2 extending in the pitch axis direction, and can change the relative angle of the connected right thigh link 38 and right lower leg link 40 around the rotation axis C2. The right ankle joint 36 has a rotation axis C3 extending in the pitch axis direction, and can change the relative angle of the connected right lower leg link 40 and right foot link 42 around the rotation axis C3.

A spring 20 is inserted in the trunk link 10 and the right thigh link 38. The spring 20 is inserted between the trunk link 10 and the right thigh link 38 behind the right thigh link 38. One end of the spring 20 is rotatably connected to a trunk side spring support point 10 p provided on the trunk link 10. The other end of the spring 20 is rotatably connected to a right leg spring support point 38p provided on the right thigh link 38.
The spring 20 is set to have a natural length when the relative angle θ is zero degrees. The relative angle θ when the spring 20 has a natural length is referred to as a neutral relative angle. That is, in this embodiment, the neutral relative angle is zero degrees. Note that the relative angle when the right leg 30 swings most forward with respect to the trunk link 10 during walking is referred to as a front-end relative angle, and the right leg 30 moves most rearward with respect to the trunk link 10 during walking. The relative angle when swinging is called the rear end relative angle.
The right thigh link 38 and the trunk link 10 are coupled so as to be rotatable about the rotation axis C1. Therefore, the elastic force generated by the spring 20 applies torque around the rotation axis C <b> 1 to the right leg 30.
When the relative angle θ changes, the length of the spring 20 also changes, and an elastic force proportional to the length of the spring 20 is generated in the longitudinal direction of the spring 20. As shown in FIG. 1, when the right thigh link 38 is swung forward, the spring 20 extends beyond the natural length, and thus the spring 20 generates an elastic force F in the compression direction. The elastic force F generated by the spring 20 acts on the trunk link 10 as a torque that causes the right thigh link 38 to swing backward about the rotation axis C1. In other words, due to the elastic force F in the compression direction generated by the spring 20, torque that swings the right leg 30 backward about the rotation axis C <b> 1 acts on the trunk link 10.
In addition, when the right thigh link 38 swings backward with respect to the trunk link 10, the spring 20 becomes shorter than the natural length, and thus an elastic force in the extending direction is generated in the spring 20. Due to the elastic force in the extending direction generated by the spring 20, torque that swings the right leg 30 forward about the rotation axis C <b> 1 acts on the trunk link 10.

The left leg 50 will be described. The left leg 50 includes a left thigh link 58, a left lower leg link 60, and a left foot link 62. The left leg 50 has a left hip joint 52, a left knee joint 54, and a left ankle joint 56.
Since the structure of the left leg part 50 is the same as that of the right leg part 30, description thereof is omitted. Although omitted in FIG. 1, the spring 20 is interposed between the trunk link 10 and the left thigh link 58 of the left leg 50, as with the right leg 30.
In addition, a motor (not shown) is built in each joint of the left leg 50, and the relative angle between the links connected to the joint can be changed by the motor outputting torque.

  In addition, the right leg part 30 and the left leg part 50 may have a joint rotatable around the roll axis and a joint rotatable around the yaw axis in addition to the above joints.

  The legged robot 100 controls the motors built in the respective joints as appropriate, that is, each motor outputs a predetermined torque as appropriate, whereby the right leg 30 and the left leg 50 are alternately moved back and forth. You can walk while swinging. Description of the control algorithm for causing the legged robot 100 to walk is omitted.

With reference to FIG. 2, the operation of the legs of the legged robot during walking will be described. In particular, the action of the spring 20 will be described.
FIG. 2 (A) shows the posture of the leg during walking. (A)-(e) has shown the attitude | position of the leg part of the legged robot 100 in the predetermined timing at the time of a walk when it observes from a pitch-axis direction. Time has passed from timing (a) to timing (e). In FIG. 2A, the right leg 30 is represented by a thick line. FIG. 2A is a view showing the posture of the right leg portion 30 and the left leg portion 50 as a whole, and the individual parts such as the spring 20 are not shown, and symbols such as joints are shown. The illustration is also omitted.
Timing (a) is the moment when the right leg 30 leaves the floor behind the trunk link 10. Timing (b) is when the right leg 30 is in a free leg state and the relative angle θ around the rotation axis C1 between the trunk link 10 and the right thigh link 38 is zero degrees. Hereinafter, the relative angle θ around the rotation axis C1 between the trunk link 10 and the right thigh link 38 may be referred to as the relative angle θ of the right leg 30 or simply as the relative angle θ. Timing (c) is the moment when the right leg 30 is landed in front of the trunk link 10. Timing (d) is when the right leg 30 is in a standing state and the relative angle θ of the right leg 30 is zero degrees. Timing (e) is again the moment when the right leg 30 leaves the trunk link 10 behind the trunk link 10. That is, the posture of the leg at the timing (e) is the same as the posture of the leg at the timing (a). Further, from timing (a) to timing (e) represents one walking cycle. Hereinafter, description will be made by paying attention to the change in the relative angle θ of the right leg 30 in one walking cycle shown in FIG.

FIG. 2B schematically shows a change with time of the relative angle θ of the right leg 30. FIG. 2C schematically shows the change over time of the torque output by the right hip joint 32 of the right leg 30. In other words, the relative angle θ shown in FIG. 2B is realized by outputting the torque shown in FIG. The “torque output by the right hip joint 32” is torque for rotating the right thigh link 38 with respect to the trunk link 10, and the motor built in the right hip joint 32 outputs the torque. And torque generated around the rotation axis C <b> 1 of the right hip joint 32 due to the elastic force of the spring 20.
FIG. 2B shows a general tendency of the change with time of the relative angle θ, and does not strictly show the actual change with time of the relative angle θ. For example, immediately after the right leg 30 leaves the floor at the timing (a), the relative angle θ may decrease rapidly and then gradually change. However, the general tendency of the change with time of the relative angle θ is shown in FIG. Similarly, FIG. 2C is a graph showing a general tendency of change in torque with time. As described above, the torque shown in FIG. 2C may mean the torque output by the right hip joint 32, or may mean the torque output by the motor built in the right hip joint 32. However, here, the reduction ratio between the output shaft of the motor and the rotation shaft of the joint is assumed to be “1”.
FIG. 2D is a graph showing a change with time of the angular velocity dθ of the relative angle θ shown in FIG. The graph of FIG. 2D is obtained by time differentiation of the graph of FIG.
2 (A), (B), (C), and FIG. 2 (D) show the passage of time from left to right, and a broken line extending in the vertical direction of the drawing represents one timing. Show.

Timing (a) is the moment when the right leg 30 leaves the floor behind the trunk link 10. The state at this time is a state in which the right leg 30 swings most backward with respect to the trunk link 10. Let θr at this time be θr. θr corresponds to the aforementioned rear end relative angle.
The right leg 30 that has left the floor at timing (a) is swung forward. In other words, the right leg 30 that has left the floor at the timing (a) is accelerated forward. The right leg 30 swung out forward has a relative angle θ of zero degrees at timing (b), is swung out further forward, and is landed at timing (c). The state when the right leg 30 is landed at the timing (c) is the state in which the right leg 30 swings most forward with respect to the trunk link 10. The right leg 30 is decelerated in preparation for landing at timing (c) while swinging forward. In other words, the right leg 30 that has accelerated forward is decelerated from timing (b) to timing (c). The relative angle θ when the right leg 30 at the timing (c) swings most forward with respect to the trunk link 10 is defined as θf. θf corresponds to the aforementioned front end relative angle.
When the right leg 30 is landed at the timing (c), the left leg 50 swings most backward with respect to the trunk link 10. Timing (c) is a state in which the left and right legs are switched at timing (a). In other words, the timing (c) is also the moment when the left leg 50 leaves the floor. After timing (c), the left leg 50 is swung out forward of the trunk link 10 and the trunk link 10 is moved forward relative to the right leg 30. In other words, the right leg 30 as a standing leg is observed from the trunk link 10 and accelerated relatively backward.
The right leg 30 observed from the trunk link 10 and accelerated rearward has a relative angle θ of zero degrees at timing (d). The right leg 30 decelerates from timing (d) to timing (e) and stops with respect to the trunk link 10 at timing (e).
After timing (e), the operation from timing (a) is repeated again.
As described above, the spring 20 is set to have a natural length when the relative angle θ is zero degrees. That is, when the relative angle θ is zero degrees, the spring 20 does not generate an elastic force. When the angle is zero degrees, the relative angle θ is referred to as a neutral relative angle θn. In the present embodiment, the neutral relative angle θn is a value approximately in the middle between the rear end relative angle θr and the front end relative angle θf.

From timing (a) to (e) is one walking cycle Tw. During one walking cycle Tw, the relative angle θ of the right leg 30 is: rear end relative angle θr−zero degree (neutral relative angle θn) −front relative angle θf−zero degree (neutral relative angle θn) −rear end relative. It changes with the angle θr. Further, the period from timing (a) to timing (c) is a period in which the right leg 30 is a free leg, and the period from timing (c) to timing (e) is the right leg 30 to be a stance. It is a period. Here, one walking cycle Tw can be divided into the following four periods.
(I) First leg of swing: Period from timing (a) to timing (b). This period is a period in which the right leg 30 is a free leg and the relative angle θ is within the range between the rear end relative angle θr and the neutral relative angle θn.
(II) Late swing phase: Period from timing (b) to timing (c). This period is a period in which the right leg 30 is a free leg and the relative angle θ is within the range between the neutral relative angle θn and the front end relative angle θf.
(III) Early stance: Period from timing (c) to timing (d). This period is a period in which the right leg 30 is a standing leg and the relative angle θ is within the range between the neutral relative angle θn and the front end relative angle θf.
(IV) Late stance: Period from timing (d) to timing (e). This period is a period in which the right leg 30 is a standing leg and the relative angle θ is within the range between the neutral relative angle θn and the rear end relative angle θr.

  The change with time of the relative angle θ of the right leg 30 is shown in FIG. The change with time of the relative angle θ is realized by the torque output from the right hip joint 32. The change with time of the torque output by the right hip joint 32 is shown by a broken line in FIG. When the spring 20 shown in FIG. 1 is not added, the torque output by the right hip joint 32 is all covered by a motor built in the hip joint 32. Accordingly, when the spring 20 is not added, the torque to be output by the right hip joint 32 is the torque to be output by the motor built in the hip joint 32.

  As shown in FIG. 2B, the change with time of the relative angle θ is substantially a sine curve. Therefore, the temporal change in angular acceleration obtained by differentiating the relative angle θ twice with time is a sine curve having the same phase as the change with time of the relative angle θ. The change over time of the angular acceleration and the change over time of the torque are substantially in phase (ignoring the damping element), and as a result, as shown in FIGS. 2B and 2C, the torque changes over time. The change is a sine curve having the same phase as the change with time of the relative angle θ.

Next, the action of the spring 20 will be described. As shown in FIG. 1, the spring 20 is interposed between the trunk link 10 and the right thigh link 38 behind the right thigh link 38. Therefore, when the right leg 30 swings backward, the spring 20 is compressed. Conversely, when the right leg 30 swings forward, the spring 20 is extended.
In the first leg of the free leg of (I), the relative angle θ is within the range from the rear end relative angle θr to the neutral relative angle θn, and the spring 20 is compressed from the natural length. Accordingly, the torque Ta acting around the rotation axis C1 due to the elastic force generated by the spring 20 is a torque in a direction for swinging the right leg 30 forward (see timing (a)). . In other words, the torque Ta based on the spring 20 acts in the direction in which the right leg 30 is accelerated forward.
In the later stage of the swing leg (II), the relative angle θ is in the range from the neutral relative angle θn to the front end relative angle θf, and thus the spring 20 is in an extended state from the natural length. Therefore, the torque Ta that acts around the rotation axis C1 due to the elastic force generated by the spring 20 is a torque that swings the right leg 30 backward (see the timing (c) diagram). . In other words, the torque Ta based on the spring 20 acts in a direction to decelerate the forward movement of the right leg 30.
In the early stance phase of (III), the relative angle θ is in the range from the neutral relative angle θn to the front end relative angle θf, as in the later stage of the free leg of (II), so that the spring 20 is extended beyond the natural length. It becomes. Therefore, the torque Ta that acts around the rotation axis C1 due to the elastic force generated by the spring 20 is a torque that swings the right leg 30 backward (see the timing (c) diagram). . During this period, the right leg 30 swings rearward relative to the trunk link 10, so the torque Ta acts in a direction that accelerates the rearward movement of the right leg 30.
In the late stance phase of (IV), the relative angle θ is in the range from the rear end relative angle θr to the neutral relative angle θn in the same manner as in the early swing leg phase of (I), so the spring 20 is compressed more than the natural length. It becomes a state. Therefore, the torque Ta acting around the rotation axis C1 due to the elastic force generated by the spring 20 is a torque in a direction for swinging the right leg 30 forward (see timing (e)). . During this period, the right leg 30 swings backward relative to the trunk link 10, so the torque Ta acts in a direction to decelerate the backward movement of the right leg 30.

The torque Ta acting around the rotation axis C1 due to the elastic force generated by the spring 20 can also be described as follows. The elastic force generated by the spring 20 is substantially proportional to the change from the natural length of the length of the spring 20. The length of the spring 20 and the relative angle θ are in a proportional relationship. In particular, in the legged robot 100, since the spring 20 is set to have a natural length when the relative angle θ is zero degrees, the value of the relative angle θ itself changes from the natural length of the length of the spring 20. It is almost proportional to the minute. Therefore, the torque Ta can be expressed as Ta = K · θ. Here, K is obtained by converting the elastic coefficient of the spring 20 into an elastic coefficient around the rotation axis C1. That is, the change with time of the torque Ta draws a curve having the same phase as the relative angle θ shown in FIG.
Here, as understood from FIGS. 2B and 2C, the change with time of the relative angle θ and the change with time of the torque to be output by the right hip joint 32 are in phase. Therefore, the torque Ta generated around the rotation axis C1 due to the elastic force of the spring 20 has the same phase as the torque that the right hip joint 32 should output in order to realize the relative angle θ. This is because the torque Ta generated around the rotation axis C1 due to the elastic force of the spring 20 assists the torque to be output by the motor of the right hip joint 32 in order to realize the relative angle θ. Means to work. The motor of the right hip joint 32 is an amount obtained by subtracting the torque Ta generated around the rotation axis C1 due to the elastic force of the spring 20 from the “torque to be output by the right hip joint 32” indicated by a broken line in FIG. It is sufficient to output a torque of. When the spring 20 is added, the change over time in the torque to be output by the motor of the right hip joint 32 is a graph indicated by a solid line in FIG. That is, the graph indicated by the solid line in FIG. 2C represents the torque that should be output by the motor of the right hip joint 32 when the spring 20 assists.
As described above, the graph indicated by the broken line in FIG. 2C is the torque that the motor of the right hip joint 32 should output when the spring 20 is not added. That is, the graph indicated by the broken line in FIG. 2C represents the torque that should be output by the motor of the right hip joint 32 when the spring 20 is not assisted. As can be understood from FIG. 2C, the spring 20 outputs a torque that assists the torque to be output by the motor of the hip joint 32 in order to cause the legged robot 100 to walk.
The same effect can be obtained for the left leg 50. Torque output by the motor of the pitch axis hip joint during walking can be reduced by a spring inserted between each leg and the trunk link 10.

The action of the spring 20 can be understood from the viewpoint of energy as follows. FIG. 2D shows the change with time of the angular velocity dθ of the relative angle θ. The temporal change in the angular velocity dθ is obtained by time-differentiating the relative angle θ shown in FIG. 2B, and the phase is shifted by 90 degrees with respect to the relative angle θ.
As shown in FIG. 2D, the absolute value of the angular velocity dθ decreases from timing (b) to timing (c). That is, the kinetic energy of the right leg 30 decreases with the passage of time in the later stage of the free leg (II). On the other hand, as shown in FIG. 2B, the absolute value of the relative angle θ increases with the passage of time in the later stage of the free leg of (II). Since the absolute value of the relative angle θ is substantially proportional to the change of the length of the spring 20 from the natural length, the elastic energy accumulated in the spring 20 is substantially proportional to the square of the relative angle θ. Accordingly, the elastic energy accumulated in the spring 20 increases with the passage of time in the later stage of the swing leg (II). This indicates that the kinetic energy of the right leg 30 is converted into the elastic energy of the spring 20 with the passage of time in the later stage of the free leg of (II). That is, in the late leg phase (II) between the timing (b) and the timing (c), the elastic force of the spring 20 acts in the direction of decelerating the forward swinging operation of the right leg portion 30, thereby The kinetic energy of the part 30 is converted into the elastic energy of the spring 20. As a result, elastic energy is accumulated in the spring 20.

Next, the absolute value of the angular velocity dθ increases from timing (c) to timing (d). That is, the kinetic energy of the right leg 30 increases with the passage of time in the first stance phase of (III). On the other hand, in (III), the absolute value of the relative angle θ decreases with the passage of time. That is, the elastic energy accumulated in the spring 20 decreases with the passage of time in the first stage of the stance (III). In the first stance phase (III) between the timing (c) and the timing (d), the elastic energy accumulated in the free leg spring 20 during the second phase (II) is converted into the kinetic energy of the right leg 30. As a result, the relative speed of the right leg 30 with respect to the trunk link 10 increases.
Next, the absolute value of the relative angle θ increases again from the timing (d) toward the timing (e), and the absolute value of the angular velocity dθ decreases. This is because the elastic force of the spring 20 is applied to the trunk link 10 of the right leg 30 in the late stance phase (IV) between the timing (d) and the timing (e) as in the late swing phase (II). The kinetic energy of the right leg 30 is converted into the elastic energy of the spring 20 by acting in the direction in which the relative backward movement is decelerated. As a result, elastic energy is accumulated in the spring 20.
The operation following the timing (e) is performed from the timing (a) to the timing (b). The absolute value of the relative angle θ decreases and the absolute value of the angular velocity dθ increases from timing (a) to timing (b). That is, in the first leg (I) between the timing (a) and the timing (b), the elastic energy accumulated in the spring 20 during the second stance phase (IV) is converted into the kinetic energy of the right leg 30. As a result, the relative speed of the right leg 30 with respect to the trunk link 10 increases.

  In the legged robot 100, the above-described action is seen in the entire walking cycle. In the legged robot 100, the periodic deceleration and acceleration of the right leg 30 during walking cause accumulation of elastic energy in the spring 20 and release of elastic energy from the spring 20, respectively. It corresponds to. This means that the reduced amount of kinetic energy when the right leg 30 decelerates with respect to the trunk link 10 is converted into elastic energy without being dissipated, and the right leg 30 is saved with respect to the trunk link 10. Means that it is reused to increase the kinetic energy when accelerating. That is, according to the legged robot 100, the energy consumed by the motor of the hip joint 32 during walking can be reduced.

  In particular, in the legged robot 100 of the present embodiment, the intermediate relative angle θn is a value approximately in the middle between the rear end relative angle θr and the front end relative angle θf. The magnitude of change from the natural length of the length of the spring 20 when the relative angle θ is the rear end relative angle θr, and the change from the natural length of the length of the spring 20 when the relative angle θ is the front end relative angle θf. Minutes are almost equal. The elastic energy accumulated in the spring 20 when the relative angle θ is the rear end relative angle θr is substantially equal to the elastic energy accumulated in the spring 20 when the relative angle θ is the front end relative angle θf. This means that the elastic energy once accumulated in the spring 20 is converted back into elastic energy after being converted into the kinetic energy of the leg during one walking cycle. That is, the energy balance of the spring 20 is zero (except for the energy dissipated by the viscous element). Thus, the spring 20 can effectively assist the pitch-axis hip joint motor without increasing the energy consumption of the pitch-axis hip joint motor.

  In the legged robot 100, a spring is interposed between the trunk link 10 and the left leg 50, similarly to the right leg 30. The spring of the left leg 50 also has the same effect as the spring 20 of the right leg 30.

Further, in the legged robot 100 of the present embodiment, the following relationship is established between the walking cycle Tw and the characteristics of the spring 20. The elastic coefficient around the rotation axis C1 of the spring 20 is represented by K, and the moment of inertia of the right leg 30 around the rotation axis C1 is represented by I. The period Ts of the natural vibration around the rotation axis C1 of the right leg 30 by the spring 20 can be expressed as Ts = 2π√ (I / K). In the legged robot 100, the elastic coefficient of the spring 20 is set so that the walking period Tw and the period Ts of natural vibration around the rotation axis C1 of the right leg 30 by the spring 20 substantially coincide. The elastic coefficient of the spring 20 is set similarly for the right leg 30 and the left leg 50.
As a result, the following effects can be obtained. The basic movement of the legs (right leg 30 and left leg 50) around the rotation axis C1 of the hip joint (right hip joint 32, left hip joint 52) during walking of the legged robot 100 is realized by the elastic force of the spring 20. can do. The basic exercise is an exercise in which the entire leg swings with a period Tw with respect to the trunk link 10. The motors of the hip joints (the right hip joint 32 and the left hip joint 52) supply driving force (torque) for giving a subtle change in motion that cannot be realized by elastic force, and energy dissipated by the damping elements of the legs 30 and 50. It is only necessary to apply a driving force to the legs. The motors of the hip joints (the right hip joint 32 and the left hip joint 52) of the legged robot 100 can be more effectively assisted by the spring inserted between the trunk link and each leg.
The magnitude of the moment of inertia I of the right leg 30 around the rotation axis C1 varies depending on the overall posture of the right leg 30 (the posture determined by the relative angle of the right knee joint 34 and the relative angle of the right ankle joint 36). To do. The magnitude of the inertia moment I may be fixed to a predetermined value within the fluctuation range to calculate the natural vibration period Ts by the spring. If the period Ts of natural vibration by the spring and the walking period Tw are approximately equal, the motor of the right hip joint 32 of the legged robot 100 can be effectively assisted. The same applies to the left leg 50.

Specific examples of the present invention have been described above in detail, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. For example, the number of legs of the legged robot may be four or six. Moreover, in the Example, the spring which expands / contracts linearly was employ | adopted as an elastic member inserted between a trunk link and a leg part. The elastic member inserted between the trunk link and the leg may be a coiled spring inserted between the rotation axis on the trunk link side of the hip joint and the rotation axis on the leg side.
The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of purposes at the same time, and has technical utility by achieving one of the purposes.

It is a typical side view of a legged robot. It is a figure explaining operation | movement of the leg part during a walk.

Explanation of symbols

10: trunk link 20: spring 30, 50: leg 32, 52: hip joint 34, 54: knee joint 36, 56: ankle joint 38, 58: thigh link 40, 60: right lower leg link 42, 62: foot Link 100: Legged robot

Claims (3)

A legged robot that has a trunk link and a leg portion that is swingably connected to the trunk link, and walks by swinging the leg portion around a rotation axis extending in the body side direction by a motor. ,
One end is connected to the trunk link, and the other end is connected to the leg, and an elastic force is generated according to the relative angle between the trunk link and the leg around the rotation axis to generate a force around the rotation axis. A legged robot comprising an elastic member for applying torque to a leg.   The relative angle between the trunk link and the leg when the elastic member has a natural length is the relative angle when the leg swings most forward with respect to the trunk link during walking, and the leg becomes the trunk when walking The legged robot according to claim 1, wherein the legged robot is located approximately in the middle of a relative angle when swinging most backward with respect to the link.   The elastic coefficient of the elastic member is set so that the natural vibration period of the leg portion around the rotation axis determined by the moment of inertia around the rotation axis of the leg portion and the elastic coefficient substantially matches the walking cycle of the legged robot. The legged robot according to claim 1 or 2, wherein the legged robot is provided.

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