CN112276994B - Variable-stiffness joint of symmetrical compression spring - Google Patents
Variable-stiffness joint of symmetrical compression spring Download PDFInfo
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- CN112276994B CN112276994B CN202011026233.0A CN202011026233A CN112276994B CN 112276994 B CN112276994 B CN 112276994B CN 202011026233 A CN202011026233 A CN 202011026233A CN 112276994 B CN112276994 B CN 112276994B
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- B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
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- B25J17/00—Joints
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Abstract
The invention provides a variable stiffness joint of a symmetrical compression spring, which belongs to the field of bionic robots and comprises a base, a joint connecting rod, a position motor, a stiffness motor and a stiffness adjusting module, wherein the stiffness adjusting module is composed of a symmetrical structure consisting of a roller, cam plates arranged on two sides and a spring, the roller is connected to a roller retainer, the position motor is fixed on the base, the output end of the position motor is connected with the roller retainer, the stiffness adjusting module is arranged on the base, the joint connecting rod is fixedly connected with one cam plate, the stiffness motor is fixedly connected with the joint connecting rod, and the output end of the stiffness motor is connected with the other cam plate. The variable stiffness joint structure is composed of the roller, the cam plates symmetrically arranged on two sides of the roller and the spring, has the advantages of simple and reliable structure, small volume, capability of obtaining the same flexible effect by forward and reverse driving, large output torque and wide stiffness adjusting range, and can be applied to various different occasions as a modular design.
Description
Technical Field
The invention belongs to the field of bionic robots, and particularly relates to a symmetrical compression spring type variable stiffness joint.
Background
The flexible robot is a robot with human-like muscle characteristic and variable rigidity, and obtains flexibility through joints, wherein the joints are driven to move by a position motor, and the rigidity of the joints is adjusted by a rigidity motor; the performance of the flexible robot is directly influenced by the quality of the variable-rigidity joint.
Chinese patent publication No. CN105328711A discloses a modular variable stiffness joint, which uses a torsion spring as an elastic element, and uses a pulley mechanism and a rope to drive and reduce the occupied space of a driving part, so that the modular variable stiffness joint has the advantages of small volume, high integration level, and the like, is suitable for applications such as exoskeleton joints, but is limited by the characteristics of the torsion spring, resulting in a narrow range of adjusting stiffness and low output torque. Chinese patent publication No. CN105108771A discloses a variable stiffness robot joint structure, which is designed based on a variable lever principle, and adopts a leaf spring as an elastic element to realize stiffness adjustment by changing a lever fulcrum, and has a wide stiffness adjustment range, but has the problems of low energy utilization efficiency, low integration level due to a complex actuator, high control difficulty, and the like. Therefore, the variable stiffness joint with wide stiffness adjustment range and high energy density needs to be developed.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a symmetrical compression spring type variable stiffness joint based on a curved cam, which has a wide adjustment range and high energy density, is suitable for flexible robots with various different performance requirements, and is beneficial to modular design.
The present invention achieves the above-described object by the following technical means.
A variable stiffness joint of a symmetrical compression spring comprises a base, a joint connecting rod, a position motor, a stiffness motor and a stiffness adjusting module; the joint connecting rod is movably connected with the base through the rigidity adjusting module, the position motor is fixed on the base, and the rigidity motor is fixedly connected with the joint connecting rod;
the rigidity adjusting module is of a symmetrical structure and comprises rollers, roller retainers, cam plates and springs, wherein two adjacent rollers form a pair of roller pairs, the roller pairs are uniformly connected to the outer rings of the roller retainers along the circumferential direction, the cam plates are arranged on two sides of the rollers, a plurality of arc-shaped bulges are arranged at equal intervals on the inner end surfaces of the cam plates, the two cam plates are overlapped to form a plurality of rolling grooves, the roller pairs are respectively positioned in the rolling grooves, and the outward end surfaces of the cam plates on two sides are connected with the springs;
the rigidity adjusting module is arranged on the base through a bearing, the output end of the position motor is connected with the roller retainer, the joint connecting rod is fixedly connected with one cam plate close to the base, and the output end of the rigidity motor is connected with the other cam plate.
Further, the rolling groove side curve is an exponential curve, and the expression of the exponential curve is as follows:
where a is the base of the exponential function, pcharIn order to be a parameter of the shape,
is a specified amount of deformation.
Further, the exponential curve has its parameters determined by the following optimization equation:
where δ S is the amount of compression of the joint and Nd is the number of designated discretized points.
Further, the spring is a compression spring and is a disc spring.
Further, the spring constant of the spring is variable.
Furthermore, a limit stop is arranged between the cam plates.
Further, the number of the rollers is three.
Further, the included angle between each pair of rollers is 15 °.
The invention has the beneficial effects that:
(1) the variable-stiffness joint structure is composed of the rollers, the cam plates symmetrically arranged on two sides of the rollers and the springs, and is simple and reliable in structure, small in size and capable of achieving the same flexible effect in forward and reverse driving; and because the invention adopts the disk spring which has the characteristic of generating larger elasticity by smaller deformation, the variable-stiffness joint has larger output torque and wide application range by applying the disk spring to the structures of the roller and the cam plate.
(2) The curve of the side edge of the rolling groove is an exponential dotted line, and the exponential curve has the characteristic that the slope increases towards one side, so when the roller is at the initial balance position, the slope of the rolling groove is gentle, and the position motor inputs a small starting torque, so that the roller can be driven to roll towards one side in a deviating manner, and the joint response is faster.
(3) The rigidity of the variable-rigidity joint is adjusted in such a way by changing the angle position between the two cam plates, namely adjusting the length of the rolling groove, and the rigidity adjusting range is wide.
(4) The invention can be used as a module, on the basis of not changing the overall dimension, different stiffness characteristic curves and output torques can be obtained by selecting the index curves with different shapes and the disc springs with different elasticity, thereby meeting different stiffness characteristic requirements; the invention also provides an optimization equation of the exponential curve, and a proper exponential curve can be selected through the optimization equation so as to meet the requirement of the rigidity curve.
(5) The invention ensures the safe and reliable operation of the joint by arranging the limit stop for direct mechanical limit protection and by the index curve and the indirect limit action of the disc spring.
Drawings
FIG. 1 is a block diagram of a variable stiffness joint of the present invention;
FIG. 2 is a block diagram of a stiffness adjustment module of the present invention;
FIG. 3 is a top view of a stiffness adjustment module of the present invention;
FIG. 4(a) is a simplified schematic illustration of the mating relationship of the roller pair with the cam plate with the rollers of the present invention in an initial equilibrium position;
FIG. 4(b) is a schematic view of the engagement of the roller pair with the cam plate in a driven state of the rollers of the present invention;
fig. 4(c) is a schematic view showing the fitting relationship between the roller pair and the cam plate in the rigidity-adjusted state of the present invention.
Detailed Description
Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
The variable stiffness joint shown in fig. 1 comprises a base 1, a joint connecting rod 2, a position motor 3, a stiffness motor 4 and a stiffness adjusting module 5; the position motor 3 is fixed on one side of the base 1, the other side of the base 1 is connected with the joint connecting rod 2, the rigidity adjusting module 5 is arranged between the base 1 and the joint connecting rod 2, the joint connecting rod 2 can rotate relative to the base 1 through the rigidity adjusting module 5, and the rigidity motor 4 is fixed on one side, far away from the base 1, of the joint connecting rod 2.
As shown in fig. 2, the rigidity adjusting module 5 is of a symmetrical structure, a roller retainer 54 is arranged in the middle, three pairs of rollers 53 are connected to the side surface of the roller retainer 54 at equal intervals along the circumferential direction, and as shown in fig. 3, an included angle α between each pair of rollers is 15 °; two sides of the roller 53 are respectively provided with a cam plate 52, the cam plates 52 are in a disc structure, the inner end surfaces of the cam plates 52 are provided with three arc-shaped bulges at equal intervals, the curve of the arc-shaped bulges expanded along the circumferential direction is an exponential curve, the two cam plates 52 are combined, a rolling groove is formed between the arc-shaped bulges of the two cam plates 52, the rolling groove is provided with three positions, and three pairs of rollers 53 are respectively positioned in the three rolling grooves and are in rolling fit with the rolling grooves; the outward end surfaces of the two cam plates 52 are both connected with springs 51, and the springs 51 are disc springs. The two cam plates 52 can rotate relatively, so that the length of the rolling groove along the circumferential direction changes along with the change of the angle position between the two cam plates 52, the two cam plates 52 can also move axially, and a limit stop is arranged between the two cam plates 52 to limit the moving range of the cam plates 52.
The rigidity adjusting module 5 is arranged on the base 1 through a crossed roller bearing, so that the compactness in the joint is improved while the axial loading capacity is ensured; the output end of the position motor 3 is connected with the roller retainer 54 through the harmonic reducer and the position output shaft in sequence; the joint connecting rod 2 is fixedly connected with a cam disc 52 close to the base 1, and the output end of the rigidity motor 4 is connected with the cam disc 52 far away from the base 1 through a harmonic reducer and a flange in sequence. The position motor 3 is used for driving the roller retainer 54 to rotate, the joint connecting rod 2 rotates along with the rotation of the cam disc 52, the rigidity motor 4 is used for adjusting the relative angular position between the two cam discs 52, and when the rigidity motor 4 is not in operation, the angular position between the two cam discs 52 is kept unchanged but can still move axially.
The principle of the variable stiffness joint of the invention is as follows:
fig. 4(a) - (c) are schematic views showing the fitting relationship between a pair of rollers 53 and a cam plate 52 developed in the circumferential direction;
as shown in fig. 4(a), when no external force is applied, the cam plates 52 on both sides are applied by the springs 51 connected to each other to press the rollers 53, the pair of rollers 53 are in a stress equilibrium position in the middle of the rolling grooves formed by the cam plates 52 on both sides, the output torque of the rollers 53 on the cam plates 52 is zero, the elastic force of the springs 51 is called initial pre-tightening force, and the stiffness of the joint is provided by the initial pre-tightening force of the springs 51;
as shown in fig. 4(b), when the roller holder 54 is driven by the position motor 3, the roller 53 is biased to one side from the equilibrium position relative to the cam plate 52 by the external force of the roller holder 54, and because the side of the rolling groove is curved, the cam plate 52 is pressed by the roller 53 while the roller 53 is biased to one side, the pressing force can be divided into two forces along the moving direction of the roller 53 and perpendicular to the moving direction (i.e. axial direction) of the roller 53, the perpendicular force makes the cam plate 52 move along the axial direction and presses the spring 51, the spring 51 is compressed and deformed to provide reverse elastic force, and the reverse elastic force provided by the compression of the spring 51 is increased along with the increase of the offset of the roller 53, and the output torque is increased; when the roller 53 is deflected to a certain extent and the reverse elasticity of the spring 51 is large enough to be compressed, the output torque of the roller 53 acting on the cam disc 52 drives the cam disc 52 to rotate, and the cam disc 52 drives the joint connecting rod 2 connected with the cam disc 52 to rotate; the driving process is embodied as joint flexibility; and because the rigidity adjusting module 5 adopts a symmetrical structure, and the cam disks 52 on the two sides are the same as the spring 51, the same flexibility can be obtained when the position motor 3 drives the joint connecting rod 54 to rotate in the forward direction and the reverse direction.
As shown in fig. 4(c), the stiffness motor 4 drives one cam plate 52 connected to the other cam plate 52 to rotate, that is, the angular position between the two cam plates 52 is changed, and the length of the rolling groove formed between the two cam plates 52 is changed; when the length of the rolling groove is reduced, the roller 53 extrudes the cam plates 52 on two sides along the arc-shaped curve of the rolling groove, the spring 51 is compressed, the initial pretightening force is increased, and the rigidity of the joint is increased; on the contrary, when the length of the rolling groove is increased, the rigidity of the joint is reduced; the rigidity motor 4 changes the joint rigidity in the above mode.
The variation relationship between the offset of the roller 53 and the output torque is related to the elasticity of the spring 51 and the arc-shaped curve of the side edge of the rolling groove;
the spring 51 is a disc spring, has a larger elastic coefficient compared with a common compression spring, and can generate larger elastic force through smaller deformation in a limited space, so that the invention has larger output torque with smaller volume; the disc spring can be regarded as being formed by combining a plurality of common springs in an overlapping and back-folding mode, wherein the overlapping can be understood as that two common springs are connected in series, and the back-folding can be understood as that two common springs are connected in parallel, and the spring 51 with different elastic coefficients can be obtained on the premise of not changing the size of the spring by changing the combined structure of the overlapping and the back-folding in the disc spring, so that the variable-stiffness joints with different stiffness characteristics can be obtained by replacing the springs 51 with different elastic coefficients on the premise of not changing the external dimension of the invention, and the feasibility is provided for the modular application of the invention.
The side arc curve of the rolling groove, namely the curve developed by the arc bulge on the cam disc 52 along the circumferential direction, is an exponential curve, and the expression of the curve is as follows:
where a is the base of the exponential function, pcharIs a shape parameter. By optimizing the base number and the shape parameters, the fitting of a given output torque and deformation curve can be realized, and the specific process is as follows:
s1: will specify the amount of deformation
Discretizing the curve of the sum moment tau to obtain a data pair of the deformation and the moment
Where Nd is the number of designated discretized points.
S2: the stiffness factor K is given, as well as the distance R (theoretically, the radius of the cam plate 52) from the contact point of the cam plate 52 with the roller 53 to the axis of the cam plate 52, depending on the size of the variable stiffness joint.
S3: according to the camThe data pair of the compression amount δ S (i.e., the displacement amount of the roller 53) and the deformation amount is calculated from τ KR δ S based on the force relationship between the disk 52 and the roller 53
S4: establishing adjustment parameter and data pairs of cam index curve
The optimization equation of (c):
according to the rigidity curve and the external dimension of the variable rigidity joint with specified requirements, the required exponential curve can be obtained through the optimization equation.
In order to ensure the reliability of joint movement, the rigidity adjusting module has three limit protections:
the movable range of the cam disc 52 is directly limited mechanically by a limit stop between the two cam discs 52, so that the joint is prevented from being out of control when indirect limit fails; the arc curve of the side edge of the rolling groove adopts an exponential curve, and the slope increases gradually towards one side under the characteristic of the exponential curve, so that the side edge of the rolling groove tends to be vertical when the roller 53 deviates towards one side in the rolling groove, thereby increasing the barrier to the rolling of the roller 53 and playing an indirect limiting role; the belleville spring has a compression limit, and cannot be compressed any more when reaching the compression limit, so that the stroke of the roller 53 is indirectly limited and protected.
The present invention is not limited to the above-described embodiments, and any obvious improvement, replacement or modification by those skilled in the art can be made without departing from the spirit of the present invention.
Claims (5)
1. The utility model provides a variable rigidity joint of symmetry formula compression spring which characterized in that: the device comprises a base (1), a joint connecting rod (2), a position motor (3), a rigidity motor (4) and a rigidity adjusting module (5); the joint connecting rod (2) is movably connected with the base (1) through the rigidity adjusting module (5), the position motor (3) is fixed on the base (1), and the rigidity motor (4) is fixedly connected with the joint connecting rod (2);
the rigidity adjusting module (5) is of a symmetrical structure and comprises rollers (53), roller holders (54), cam plates (52) and springs (51), two adjacent rollers (53) form a pair of roller pairs, the roller pairs are uniformly connected to the outer rings of the roller holders (54) along the circumferential direction, the cam plates (52) are arranged on two sides of the rollers (53), a plurality of arc-shaped bulges are arranged on the inner end surfaces of the cam plates (52) at equal intervals, the two cam plates (52) are overlapped to form a plurality of rolling grooves, the roller pairs are respectively positioned in the rolling grooves, the outward end surfaces of the cam plates (52) on two sides are connected with the springs (51), and the springs (51) are compression springs and disc springs;
the rigidity adjusting module (5) is arranged on the base (1) through a bearing, the output end of the position motor (3) is connected with the roller retainer (54), the joint connecting rod (2) is fixedly connected with one cam plate (52) close to the base (1), and the output end of the rigidity motor (4) is connected with the other cam plate (52);
the side curve of the rolling groove is an exponential curve, and the expression of the exponential curve is as follows:
where a is the base of the exponential function, pcharIn order to be a parameter of the shape,
is a specified deformation amount;
the exponential curve has its parameters determined by the following optimization equation:
where δ S is the amount of compression of the joint and Nd is the number of designated discretized points.
2. The variable rate joint of a symmetrical compression spring of claim 1, wherein: the spring constant of the spring (51) is variable.
3. The variable rate joint of a symmetrical compression spring of claim 1, wherein: limit stops are arranged between the cam plates (52).
4. The variable rate joint of a symmetrical compression spring of claim 1, wherein: the number of the rollers (53) is three.
5. The variable rate joint of a symmetrical compression spring of claim 4, wherein: the included angle between each pair of rollers (53) is 15 degrees.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202011026233.0A CN112276994B (en) | 2020-09-25 | 2020-09-25 | Variable-stiffness joint of symmetrical compression spring |
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| Application Number | Priority Date | Filing Date | Title |
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| CN202011026233.0A CN112276994B (en) | 2020-09-25 | 2020-09-25 | Variable-stiffness joint of symmetrical compression spring |
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| CN112276994B true CN112276994B (en) | 2021-10-12 |
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| KR101412130B1 (en) * | 2008-03-14 | 2014-06-27 | 삼성전자주식회사 | Compliant Joint |
| CN102561520B (en) * | 2011-12-31 | 2014-03-19 | 福建龙溪轴承(集团)股份有限公司 | Radial spherical plain bearing gliding node with rest function |
| CN203460186U (en) * | 2013-07-15 | 2014-03-05 | 北京理工大学 | Elastic component capable of providing non-linear variable stiffness |
| CN104985608B (en) * | 2015-06-23 | 2017-01-18 | 浙江大学 | Stiffness-adjustable flexible joint actuator mechanism |
| CN106426267B (en) * | 2016-08-31 | 2018-09-14 | 华南理工大学 | A kind of continuously adjustable joint of the rigidity based on floating spring |
| CN108228980A (en) * | 2017-12-19 | 2018-06-29 | 江南大学 | A kind of Cover whirling Machine Design of cam curves method based on fitting of a polynomial |
| CN110202610B (en) * | 2019-04-26 | 2023-06-23 | 南京航空航天大学 | Bionic cam type active elastic vertebra joint and working method thereof |
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