CN109129560B

CN109129560B - Flexible waist structure suitable for biped robot and design method thereof

Info

Publication number: CN109129560B
Application number: CN201811001524.7A
Authority: CN
Inventors: 甘春标; 能一鸣; 田蒋仁; 袁海辉; 徐小锋; 叶靖; 朱小京
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2018-08-30
Filing date: 2018-08-30
Publication date: 2020-08-14
Anticipated expiration: 2038-08-30
Also published as: CN109129560A

Abstract

The invention relates to a flexible waist structure model suitable for a biped robot and a design method thereof, which introduces an elastic series drive (SEA) into the design of the waist structure of the biped robot, realizes the flexibility in two degrees of freedom of pitching and swinging by a group of compact elastic structures, can effectively improve the mechanical characteristics of a waist steering engine and reduce impact load, and also has the function of protection and limit. Meanwhile, a plurality of design principles and a complete design process of the flexible waist structure are given.

Description

Flexible waist structure suitable for biped robot and design method thereof

Technical Field

The invention belongs to the technical field of robots, and provides a two-degree-of-freedom flexible waist structure suitable for a biped robot and a design method thereof.

Background

A biped robot is a robot that mimics the structural features of a human being, with the ultimate goal of achieving similar motion behavior as a human being. At present, the mainstream biped robot realizes the deviation of the whole mass center by means of the deflection of hip joints and ankle joints, and further realizes various motions. Under the motion mode, the robot has large torsional pendulum amplitude and low stability, and has larger difference with the walking posture of the human. The introduction of the waist can drive the mass center to deflect through the auxiliary motion of the upper half body, so as to reduce the deflection amplitude of the hip joint and the ankle joint and make the gait more humane.

Because the upper half body of the robot integrates various control, sensing and functional elements, the moment of inertia is large, and the requirement on the mechanical property of the steering engine is high; when the robot is started or stopped, impact is easily generated, and the stability of the robot is affected. And the introduction of the elastic element can reduce the torque borne by the steering engine, and elastic potential energy is stored and released to reduce impact, so that the robot has important values for realizing more stable and anthropomorphic gaits and improving the practicability and durability of the waist of the robot.

Disclosure of Invention

In order to solve the above problems, the present invention provides a two-degree-of-freedom flexible waist structure for a biped robot, comprising:

the support is fixed on the robot waist base and comprises a supporting seat, a supporting rotary table which is rotatably arranged on a supporting seat beam and a protective torsion spring which is arranged between the supporting seat and the supporting rotary table, and a flange which is vertical to the beam is arranged on one surface of the supporting rotary table which is far away from the supporting seat beam;

the back of the sliding turntable is provided with a sliding chute matched with a flange on the supporting turntable, the sliding turntable is connected with the supporting turntable in a sliding mode through the sliding chute and the flange, the supporting turntable is tightly attached to the sliding turntable under the action of a protective torsion spring and rotates along with the sliding turntable, and the flange is ensured to be tightly attached to the groove; the back of the fixed turntable is fixedly connected with a turntable of the robot waist pitching freedom steering engine, and the sliding turntable and the front of the fixed turntable are connected through a shaft-sleeve structure and can move relatively in the axis direction or rotate relatively around the axis; setting the axis position in the initial state as a reference axis;

still including locating elastic element between slip carousel and the rigid coupling carousel, elastic element includes sharp elastic element and twists reverse elastic element, sharp elastic element compression sets up between rigid coupling carousel and slip carousel, and elasticity direction with the axis direction is unanimous for the flexibility of providing robot waist portion degree of freedom that sways, it connects respectively to twist reverse elastic element rigid coupling carousel and slip carousel, be used for providing the centre on the rotatory torsion of axis direction realizes the flexibility of robot waist every single move degree of freedom.

Optionally, the linear elastic element is a linear spring, and the torsional elastic element is a torsion spring or a criss-cross spring steel sheet.

The invention also provides a design method of the two-degree-of-freedom flexible waist structure, which comprises the following steps:

s1, establishing a waist model of the biped robot by using graphic software such as solidworks and the like, and determining the upper half body mass center and the moment of inertia of the robot; establishing a flexible waist pitching motion dynamic model and a flexible waist swaying motion dynamic model according to a force balance equation;

s2, determining the maximum deflection angle according to the motion mode of the biped robot; determining the elastic coefficient of the elastic element according to a dynamic equation and steering engine parameters;

s3, determining the type and the geometric dimension of the elastic element according to the elastic coefficient of the elastic element and the waist space structure of the biped robot; if the elastic element meeting the requirements cannot be obtained, establishing a height adjusting model, and redesigning the linear elastic element;

s4, determining the geometric structure and the space size of each part according to the type and the geometric dimension parameters of the elastic element and the supporting height, and designing a limiting function;

and S5, integrating the flexible mechanism obtained in the step into a rigid waist structure of the robot to obtain the flexible waist structure.

Further, in S1, the pitch motion dynamics model is:

the rocking motion dynamics model is as follows:

wherein m is the mass of the upper body of the robot, I is the product of inertia of the upper body of the robot, l is the distance from the center of mass of the upper body to a pitching/swinging rotating shaft, l ' is the pre-compression amount of a linear spring, alpha is a pitching angle, beta is a swinging angle, k and k ' are elastic coefficients of a torsional elastic element and a linear elastic element respectively, T, T ' is the torque of a steering engine on two degrees of freedom of pitching and swinging respectively, and d is the distance of a supporting reaction force action point on an axis.

Further, in S2, the elastic coefficient determination method of the elastic element is as follows:

for a torsionally elastic element, the elastic coefficient k should satisfy the following equation:

for a straight elastic element, the elastic coefficient k' should satisfy the following equation:

wherein

Related to the speed-moment (omega-t) curve of the steering engine, namely the maximum angular speed omega of the triangular speed curve of the steering engine_maxMaximum steering engine torque corresponding to lower, α_max、β_maxThe maximum pitch angle and the maximum yaw angle are respectively, and t is one gait cycle of the robot.

Further, the height adjustment model in S3 is as follows:

the axis of the supporting turntable is lifted h on the basis of the reference axis, and then the swing kinetic equation becomes

The selection range of the elastic coefficient k' becomes

Further, in S4, the limiting function is implemented as follows:

1) in the pitching degree of freedom, the contact sensor is pasted, when the fixed connection turntable is in contact with the sliding turntable, an instruction is sent to stop the steering engine, the rotation limit of the fixed connection turntable and the sliding turntable is carried out, and the maximum limit angle α is realized_max；

2) In the swing freedom, the limiting function is determined by the opposite moving distance d' between the fixed turntable and the sliding turntable in the axial direction and the maximum swing angle β_maxIn a relationship of

When the height adjustment model is adopted, the relationship is

The steering engine can be stopped by sticking the contact sensor and sending an instruction when the fixed connection turntable and the sliding turntable are in contact.

The flexible waist structure suitable for the biped robot introduces the elastic series drive (SEA) into the design of the waist structure of the biped robot, realizes the flexibility in two degrees of freedom of pitching and swinging by a group of compact elastic structures, can effectively improve the mechanical characteristics of a waist steering engine and reduce impact load, and also has the function of protecting and limiting. Meanwhile, the invention also provides a design method of the flexible waist structure to realize the flexible waist structure, so that the steering engine is reduced to bear torque, and elastic potential energy is stored and released to reduce impact, thereby having important values for realizing more stable and anthropomorphic gaits and improving the practicability and durability of the waist of the robot.

Drawings

FIG. 1 is a two-degree-of-freedom waist three-dimensional model and an abstract diagram thereof.

Fig. 2 is a schematic diagram of an elastic tandem driving improvement method suitable for a flexible waist of a biped robot.

Figure 3 is a schematic view of a flexible waist structure of the present invention.

Figure 4 is an exploded view of the flexible waist structure of figure 3.

Fig. 5 is a schematic view of a robot waist model configured with the flexible waist structure of fig. 3.

Fig. 6 is a simplified model illustration of the dynamics in the pitch degree of freedom.

FIG. 7 is a simplified model representation of dynamics in rocking degrees of freedom.

FIG. 8 is a simplified model representation of increasing the moment arm using a height adjustment model.

Fig. 9 is a schematic diagram of a two-degree-of-freedom flexible waist structure following a height adjustment model and a robot waist model configured with the same.

Fig. 10 is an exploded view of the flexible waist structure with a position limiting function according to the present invention.

Fig. 11 is a schematic flow diagram of a flexible waist structure design method of the present invention.

Detailed Description

In order that the invention may be better understood by those skilled in the art, reference will now be made in detail to the present invention as illustrated in the accompanying drawings and specific examples,

as shown in fig. 1, a two-degree-of-freedom rigid waist model is first established. Generally, the waist of the biped robot functions as an auxiliary motion and has two degrees of freedom, namely pitching and swinging. The rigid waist is the basis of the flexible waist model.

As shown in fig. 2, in order to improve the mechanical characteristics and the compliant speed output of the steering engine, it is considered to introduce elastic series drive (SEA) into two degrees of freedom in the waist. The traditional elastic series driving is to realize accurate moment control in the robot, and an elastic element is added between a driving mechanism and a driven mechanism. But the accuracy and real-time of its position control are greatly reduced. The main function of the waist structure of the biped robot is to adjust the whole mass center through accurate deflection motion, and to degrade the deflection amplitude of the hip and the ankle, so that the gait is more humane. Therefore, the elastic element is arranged externally, and the external fixing mechanism is added, so that the elastic element is more suitable for the waist structure of the biped robot.

Whereas, since the pitch degree of freedom is attached to the lumbar degree of freedom, the rotational movement in the roll degree of freedom causes a yaw of the pitch degree of freedom rotational axis. It is therefore required that the resilient member also be able to deflect in order to ensure centering. Meanwhile, the waist space of the biped robot is limited, and the available space is mainly arranged on two sides of the waist. Based on the consideration, the design method for the two-freedom-degree flexible waist structure is innovatively provided, and the flexibility in two degrees of freedom is realized through a group of compact mechanisms arranged on two sides of the waist.

As shown in fig. 3 and 4, an embodiment of the flexible waist structure of the present invention and its exploded view are shown.

The fixed turntable 1 and the sliding turntable 4 are first connected by a shaft-sleeve mechanism, the torsional elastic element 3 and the linear elastic element 2 are connected at the center, the selection of the torsional elastic element 3 can be various, in this case, a cross spring steel sheet is used, so as to obtain a higher elastic coefficient. The sliding turntable 4 is matched with the flange of the supporting turntable 54 in the support 5 through the groove 41 to realize relative sliding. The sliding turntable 4 is kept in balance by the elastic force of the linear elastic element 2 and the restraining counter force of the supporting turntable 54. The support seat 51 of the support 5 is fixed on the lumbar chassis, the support rotary disc 54 is arranged on the support beam 52 and tightly attached to the sliding rotary disc 4 to rotate along with the sliding rotary disc 4 under the action of the torsion spring 53, and the flange is ensured to be tightly attached to the groove. Since the torsion spring 53 has a very small elastic coefficient and is negligible in mechanical analysis, it can be considered that the force of the sliding turntable 44 on the supporting turntable 54 completely acts on the supporting beam 52.

Fig. 5 is a schematic view of a robot model configured with the flexible waist structure.

The embodiments presented herein are but one implementation of the two degree-of-freedom flexible lumbar structure described in the present invention and do not represent the only implementation. The specific structures of the fixed connection turntable, the sliding turntable and the elastic element can have various designs, and are not described in detail herein.

And after the two-degree-of-freedom flexible waist basic structure is obtained, the pitching degree-of-freedom and the swinging degree-of-freedom are subjected to dynamic analysis respectively so as to design parameters of parts. When the robot returns to the balance position from the torsional/pitching state, the mechanical properties of the steering engine and the spring are required to be higher due to the existence of the acceleration, and the analysis is carried out at the moment.

As shown in fig. 6, in the pitch degree of freedom, flexibility is achieved by the torsional elastic element. The mass center of the upper body of the robot corresponds to one point with mass m, the distance between the mass center and the rotation center is l, the inertia moment of the upper body of the robot relative to the point is I, the driving moment of the steering engine is T, the torsion angle is alpha, if the swing angle is beta, the gravity acceleration component gcos beta on the pitching plane is obtained, and the kinetic equation is as follows.

In the swing freedom degree, the linear elastic element is utilized to generate flexibility, the waist swing motion causes the linear elastic element to be compressed due to the geometric structure constraint, and the acting force arm changes along with the swing angle. As shown in the figure7, let l' be the precompression of the spring, the amount of compression

The elastic coefficient of the linear elastic element is k ', and F is equal to k ' (x + l '). Let the driving torque of the steering engine be T', and a dynamic model of the swinging freedom degree is as follows

Due to the limitation of the size of the waist of the biped robot, the geometrical size of the elastic element is limited, and the generated moment can be small. If the upper body of the robot is light in weight, a normal torsion spring can be used for the torsional elastic element, and in the case of a heavy upper body, a significantly larger spring constant can be obtained with a cross spring steel sheet than with a similarly sized torsion spring. The linear elastic element is generally selected from a linear spring, has a wide selectable range, and is designed according to the principle in a mechanical design manual after the elastic coefficient is determined.

Meanwhile, due to the limitation of the waist space size of the biped robot, the deformation of the linear elastic element on the swinging freedom degree cannot be too large, the instantaneous moment arm for restraining the counter force is small, and the swinging moment is small. To solve this problem, the present invention further proposes a height adjustment model. The basic idea is to lift the supporting position in the vertical direction by h, and the method can greatly increase the acting force arm of the constraint reaction force and increase the compression amount x of the spring under the condition that the deflection angles beta are the same. The force arm deflection model is adopted, the supporting force is mainly provided by one side, and the precompression forces at the two sides are mutually offset.

By raising the support turntable axis by a distance h, as shown in fig. 8, the support moment is mainly provided by one side in case of turning the same angle. One side force arm for providing supporting force

Amount of compression of spring

All are obtainedTo a significant extent. The complete kinetic equation is as follows:

because the above formula is more complicated, a smaller component is omitted after the expansion, and

fig. 9 is a schematic view of an embodiment of a flexible waist structure following the height adjustment model described above.

The key parameters to be considered are mainly the elastic coefficient k of the torsional spring element 3, the elastic coefficient k' of the linear spring element 2, and the maximum pitch angle α_maxAnd maximum rocking angle β_maxAnd the like. These parameters are related to the speed-torque (omega-T) of the steering engine_ω) Characteristics, steering engine speed curve, gait cycle t of the robot and the like. Will omega-T_ωT steering engine speed curve is regarded as given value, and α is corresponding to maximum pitch angle_maxAnd maximum rocking angle β_maxTheoretically, it takes the angle required to completely drop the center of gravity onto one foot by completely deflecting the waist. In practical application, the movement of the waist is auxiliary, and the limitation of the size of the space structure is added, so that the angle is generally 5-10 degrees.

Steering engine speed curves are generally triangular, horizontal and trapezoidal. Theoretically, the acceleration of the horizontal velocity curve at the beginning is infinite, and in practice, the acceleration cannot exceed the maximum acceleration allowed by the steering engine. In practice, to avoid shocks, the acceleration during the acceleration and deceleration phase should be as small as possible. Under the triangular curve, the acceleration is minimal, so the use of a triangular motion curve is considered. Maximum velocity and acceleration under the triangular curve are respectively

The larger the movement speed of the steering engine is, the smaller the maximum torque which can be reached is. Is composed ofAnd ensuring that the elastic element meets the requirement, and determining a lower bound of the obtained k value on the assumption that all extreme values can be obtained at the limit deflection position simultaneously during calculation. Substituting each parameter into a kinetic equation, having

It is clear that,

so that there are

For the same reason, for the freedom of swing, there are

The elastic modulus selected within this range can theoretically satisfy the requirements. After the elastic coefficient of the elastic element is determined, the type and the size of the elastic element are selected according to the space structure of the waist, and if the corresponding elastic coefficient cannot be achieved in the swinging freedom degree, the height adjustment model can be adopted to redesign the elastic element.

After the elastic elements are determined, the specific size and structure design of each part of the elements can be entered. The components may have different specific implementations, but the basic structure is consistent. In the case of determining the basic features of the waist model and the dimensional characteristics of each element, various structures can be designed.

Referring to fig. 10, the present invention provides two embodiments of flexible waist structures with a position limiting function. Wherein the embodiment in fig. 10c replaces the linear spring and the crisscrossed spring steel sheet in fig. 10b with a torsion spring 3' having both linear elasticity and torsional elasticity.

In the pitch freedom degree, the maximum limit angle is realized by the rotation limit of the fixed turntable and the sliding turntable, and the maximum pitch angle α_maxEqual to the limit angle. A contact sensor is pasted at the opening, and the steering engine can be stopped by sending an instruction during movement when in contact, so that the steering engine is not damaged. In the degree of freedom of rockingThe limiting function is determined by the compressible distance d' between the fixed turntable and the sliding turntable in the axial direction, as shown in FIG. 10a, which is equal to the maximum swing angle β_maxIs as follows

When a moment arm amplification model is adopted, the relationship is

As shown in fig. 11, the above steps are performed in sequence, and finally the flexible waist structure of the biped robot is obtained.

The prototype design examples mentioned in the above description are only illustrations of implementation forms of the technical idea of the present invention, and the scope of the present invention is not limited to the above embodiments, and the scope of the present invention can be extended to equivalent technical means that can be conceived by those skilled in the art according to the technical idea of the present invention.

Claims

1. The utility model provides a flexible waist structure suitable for biped robot which characterized in that: the robot waist support comprises a support fixed on a robot waist base, wherein the support comprises a support seat, a support rotary table rotatably arranged on a support seat cross beam and a protective torsion spring arranged between the support seat and the support rotary table, and a flange perpendicular to the cross beam is arranged on one surface of the support rotary table, which is far away from the support seat cross beam;

the back of the sliding turntable is provided with a sliding chute matched with a flange on the supporting turntable, the sliding turntable is connected with the supporting turntable in a sliding mode through the sliding chute and the flange, the back of the fixedly connected turntable is fixedly connected with a turntable of a robot waist pitching freedom steering engine, and the front faces of the sliding turntable and the fixedly connected turntable are connected through a shaft-sleeve structure and can move relatively in the axis direction or rotate relatively around the axis;

2. The flexible lumbar structure suitable for use in a biped robot of claim 1, wherein: the linear elastic element is a linear spring, and the torsional elastic element is a torsion spring or a cross spring steel sheet.

3. A design method of a flexible waist structure suitable for a biped robot as claimed in claim 1 or 2, comprising the steps of:

s1, establishing a biped robot waist model by using graphic software, and determining the upper half body mass center and the moment of inertia of the robot; establishing a flexible waist pitching motion dynamic model and a flexible waist swaying motion dynamic model according to a force balance equation;

4. The method for designing a flexible waist structure of a biped robot according to claim 3, wherein in S1, the pitch kinematics model is:

the rocking motion dynamics model is as follows:

wherein m is the upper half body mass of the robot, I is the product of inertia of the upper half body of the robot, l is the distance from the center of mass of the upper half body to the pitching/swinging rotating shaft, l ' is the pre-compression amount of the linear spring, alpha is the pitch angle, beta is the swinging angle, k and k ' are the elastic coefficients of the torsional elastic element and the linear elastic element respectively, T, T ' is the steering engine torque on the pitching and swinging degrees of freedom respectively, and d is the distance of the supporting reaction force acting point on the axis.

5. The method for designing a flexible waist structure of a biped robot according to claim 4, wherein in S2, the method for determining the elastic modulus of the elastic element is as follows:

for a linear elastic element, the elastic coefficient k' should satisfy the following equation:

wherein

Related to the speed-moment (omega-t) curve of the steering engine, namely the maximum angular speed omega of the triangular speed curve of the steering engine_maxMaximum steering engine torque corresponding to lower, α_max、β_maxAre respectively asThe maximum pitch angle and the maximum yaw angle, t, is one gait cycle of the robot.

6. The method of claim 5, wherein the height adjustment model in S3 is as follows:

The selection range of the elastic coefficient k' becomes

7. The design method of flexible waist structure for biped robot according to claim 6, wherein in S4, the position limiting function is realized by:

When the height adjustment model is adopted, the relationship is