CN110434836B

CN110434836B - Multistage passive bending mechanism based on variable cross-section crossed reed

Info

Publication number: CN110434836B
Application number: CN201910834666.XA
Authority: CN
Inventors: 曹勇; 潘光; 千哲; 贺俊杰; 黄桥高; 曹永辉
Original assignee: Northwestern Polytechnical University
Current assignee: Northwestern Polytechnical University
Priority date: 2019-09-05
Filing date: 2019-09-05
Publication date: 2022-07-05
Anticipated expiration: 2039-09-05
Also published as: CN110434836A

Abstract

The invention relates to a multi-stage passive bending mechanism based on variable cross-section crossed reeds. According to the cambered surface free end, the intersection point of the crossed reed is overlapped with the center of the unit of the crossed reed relative to the free end outside the whole bending mechanism, so that the offset of the intersection point of each crossed reed unit is reduced when the crossed reed is subjected to passive bending deformation, and the deformation precision is higher. The cross reed unit with the variable cross section is adopted, namely the cross section of each reed is thinnest at the cross point and thickest at the part connected with the free end, so that large passive deformation is realized under the condition of ensuring the deformation precision, and the deformation precision of the cross reed unit is higher under the same deformation degree.

Description

Multistage passive bending mechanism based on variable cross-section crossed reed

Technical Field

The invention belongs to the field of multi-stage passive bending mechanisms, relates to a multi-stage passive bending mechanism based on variable cross-section crossed reeds, and discloses a mechanical mechanism for realizing multi-stage bending deformation under the action of external force.

Background

The passive bending mechanism is a mechanism which generates bending deformation under the action of external force, and is a very common mechanical structure, such as a diving board of a diving athlete and a bow body of an arrow. The traditional passive bending deformation mechanism is generally similar to a simple cantilever beam, or a mechanism formed by connecting rotating mechanisms with friction, and has larger limitation in deformation. For the bending mechanism similar to the cantilever beam, the deformation precision is low because the bending mechanism is a single-stage deformation structure. In the case of a mechanism formed by connecting rotating mechanisms with friction, friction loss can cause the increase of energy consumption, the reduction of efficiency and the accumulation of deformation errors, and the influence of the traditional passive deformation mechanism on the overall performance is great in machines with higher precision requirements, such as medical instruments and high-precision robots. The passive deformation mechanism in the method of manufacturing a bendable distal end endoscope having passive bending connection disclosed in patent publication No. CN1543907A is a multi-layer bent tube structure with a single structure, and although the passive deformation range in actual use is large, the precision of controllable deformation is very limited. And besides the characteristics of the common bending mechanism, the multistage passive bending mechanism based on the crossed reeds has better deformation controllability. In 2013, volume 41 and phase 7, the passive bending mechanism adopted in the experimental study of the bionic tail fin propeller driven by the SMA wire is the SMA wire, and the passive deformation of the SMA wire is restricted by the active deformation because the SMA wire simultaneously bears the active deformation, so that the passive deformation effect of the bionic fish cannot be achieved to the maximum extent. Moreover, the conventional bending mechanism is usually made of a single elastic material, and the multi-stage passive bending mechanism has better mechanical properties than the common bending mechanism. In the aspect of practical application, the multi-stage passive bending mechanism can replace a common bending mechanism and can be applied to other more aspects, such as bionic fish fin lines, the multi-stage deformation bending mechanism can better simulate a fin line structure with joints of fish, the fin line structure of the fish is a multi-stage deformation structure formed by connecting a plurality of joints in series, and the plurality of fin lines are connected in parallel to form the fin structure.

Disclosure of Invention

Technical problem to be solved

In order to avoid the defects of the prior art, the invention provides a multi-stage passive bending mechanism based on a variable cross-section reed, which has passive bending deformation along the length direction under the action of external force and has very important significance in practical engineering application.

Technical scheme

A multi-stage passive bending mechanism based on variable cross-section crossed reeds is characterized by comprising a plurality of cambered free ends and variable cross-section crossed reeds; two equal-length reeds with variable cross sections are symmetrically and alternately connected with two adjacent cambered free ends along the length direction of the reeds to form a first stage, the cross section of each reed is thinnest at the intersection point, and is thickest at the part connected with the free ends; the rigidity of each stage of bending depends on the material and thickness of the reeds, the included angle of the two reeds and the position of the intersection point of the two reeds; the rigidity of the reeds is in direct proportion to the strength of the material, the thickness of the reeds, the included angle of the two reeds and the length proportion of the reeds on two sides of the intersection point of the two reeds, namely the ratio of the length of the side with small length to the length of the side with large length.

Two equal-length variable-section reeds are symmetrically and alternately connected with two adjacent cambered free ends along the length direction of the reeds to form a crossed reed unit, and a plurality of crossed reed units are connected in series to form a multi-stage passive bending mechanism.

The stiffness of the first stage reed is at a maximum.

The rigidity of the multi-stage reeds is sequentially reduced from the first-stage reeds to the last-stage reeds, so that the bending deformation of the tip close to the bending structure is larger when the tip is subjected to passive deformation caused by external force.

The rigidity of the multi-stage reeds is kept to be the maximum when the rigidity of the first stage of reeds is kept, and other stages of reeds are combined according to the required rigidity on the material and the thickness of the reeds, the included angle of the two reeds and the position of the intersection point of the two reeds.

The size of the free end of the cambered surface is sequentially reduced along the spanwise direction.

The free ends of the cambered surfaces are consistent in bending direction and are bent inwards along the spanwise direction.

Advantageous effects

The multistage passive bending mechanism based on the variable cross-section crossed reed has the advantages of high precision, no friction, no hysteresis, no abrasion, no static resistance, no lubrication and the like, and can replace a plurality of similar passive deformation structures in the aspect of practical engineering application. For example, the method can be applied to a pectoral fin propulsion structure of an underwater bionic aircraft, and can well simulate the passive deformation of the flexible pectoral fins of fishes during underwater motion.

The invention is composed of a plurality of crossed reed units with different sizes, the crossed reed units with different sizes are selected to be combined according to the linear requirements of different bending mechanisms, the structure of a single crossed reed is composed of two cambered free ends and a cross reed with variable cross section connecting the two cambered free ends, and each cross reed unit with variable cross section is formed by symmetrically interleaving two reeds with equal length along the length direction. When the passive bending mechanism is formed, the reed units are connected by the corresponding free ends to form a multi-stage crossed reed structure, so that a multi-stage passive bending motion mode is achieved. The rigidity distribution of the crossed reed unit is adjusted according to the rigidity distribution requirement of the multistage passive bending mechanism in the spanwise direction, and the rigidity of the crossed reed unit under the same external condition is related to the material and the thickness of reeds, the included angle of the two reeds and the position of a crossed point of the two reeds. The rigidity of the cross reed unit is in direct proportion to the strength of the material of the reed under the condition that other conditions are not changed, the rigidity of the cross reed unit is in direct proportion to the thickness of the reed under the condition that other conditions are not changed, the rigidity of the cross reed unit is in direct proportion to the size of an included angle of the reed under the condition that other conditions are not changed, and the rigidity of the cross reed unit is in direct proportion to the size of the length of the reeds on two sides of the cross point of the reed under the condition that other conditions are not changed (the ratio of the length of the side with the small length to the length of the side with the large length). For example, a cross-reed unit with high rigidity may be used at the root of the multi-stage passive bending mechanism, and a cross-reed unit with low rigidity may be used at the tip of the multi-stage passive bending mechanism, so that when the bending mechanism is passively deformed by an external force, the deformation of the tip bending closer to the bending mechanism is larger.

In a conventional parallel free end-based crossed reed bending mechanism, the cambered free end is adopted in the scheme, and the crossed point of the crossed reed is overlapped with the circle center of the unit of the crossed reed relative to the free end outside the whole bending mechanism, so that the offset of the crossed point is reduced when each crossed reed unit is subjected to passive bending deformation, and the deformation precision is higher. When the free end is subjected to external force, the free end is better deformed along the stress direction. The cross reed unit with variable cross section is adopted by the invention relative to the cross reed with the equal cross section of the free end of the cambered surface, namely, the cross section of each reed is thinnest at the cross point and thickest at the part connected with the free end, so that larger passive deformation is realized under the condition of ensuring the deformation precision, and the deformation precision of the cross reed unit is higher under the same deformation degree.

Compared with a rigid deformable body, the crossed reed flexible deformable body has many advantages of the crossed reed flexible deformable body, such as high precision, no friction, no hysteresis, no abrasion, no static resistance, no lubrication and the like. Based on these characteristics of the cross spring, in practical applications, the cross spring is usually used as a flexible hinge, which has a large rotation range and small stress. Therefore, the crossed reeds can be mutually connected in series to form the multistage bending deformation mechanism, compared with the traditional bending mechanism, the multistage bending mechanism based on the crossed reeds has the advantages of high rotation precision, large rotation range and small stress, and the movement process of the multistage bending mechanism based on the existing research on the crossed reeds can be well analyzed.

Drawings

FIG. 1 is a schematic view of the overall structure of the present invention

FIG. 2 is a force diagram of the overall structure of the invention

FIG. 3 is a schematic diagram of the overall structural variation of the present invention

FIG. 4 is a schematic view of cross reed unit No. 1 according to an embodiment of the present invention

FIG. 5 is a schematic view of cross reed unit No. 2 according to an embodiment of the present invention

FIG. 6 is a schematic view of cross reed unit No. 3 according to an embodiment of the present invention

FIG. 7 is a schematic view of a number 4 cross reed unit of the present invention

FIG. 8 is a schematic view of cross reed unit No. 5 according to an embodiment of the present invention

FIG. 9 is a schematic view of cross reed unit No. 6 according to an embodiment of the present invention

1-No. 1 cross reed unit, 2-No. 2 cross reed unit, 3-No. 3 cross reed unit, 4-No. 4 cross reed unit, 5-No. 5 cross reed unit, 6-No. 6 cross reed unit, 7-cambered surface free end, 8-variable cross reed

Detailed Description

The invention will now be further described with reference to the following examples and drawings:

this embodiment is a six-stage passive bending mechanism, which includes a No. 1 cross reed unit, a No. 2 cross reed unit, a No. 3 cross reed unit, a No. 4 cross reed unit, a No. 5 cross reed unit, and a No. 6 cross reed unit.

The multistage passive bending mechanism based on the crossed reeds mainly comprises crossed reed units with different sizes, wherein each crossed reed unit comprises two cambered surface free ends and a crossed reed connected with the two cambered surface free ends. The cross reed adopts a cross reed unit with variable cross section, namely the cross section of each reed is thinnest at the cross point and thickest at the part connected with the free end, so that larger passive deformation is realized under the condition of ensuring the deformation precision and under the same deformation degree. The size of the specific crossed reed is determined according to the line type of the specific multistage passive bending mechanism, and the rigidity and the size of each stage of the whole multistage bending mechanism can be controlled by changing the combination of different bending units, so that the rigidity distribution and the multistage bending deformation distribution of the whole bending mechanism can be accurately controlled. The stiffness, i.e., degree of bending, of each stage of the present embodiment is dependent on the crossing position of the crossing leaves, as shown in the bending mechanism.

From the No. 1 cross reed unit to the No. 6 cross reed unit, the rigidity is gradually increased and the bending degree is gradually reduced along with the difference of the crossing positions of the cross reeds.

The unit with smaller rigidity, namely the No. 1 crossed reed unit, can be arranged at a place with larger bending degree and softer flexibility, the unit with larger rigidity, namely the No. 6 crossed single reed unit, can be arranged at a place with smaller bending degree and larger rigidity, the whole passive bending mechanism in the figure is composed of the No. 1 to No. 6 crossed reed units, the rigidity of the No. 1 to No. 6 crossed reeds is increased in sequence, the size is also increased, and the influence of the size of the crossed reeds on the rigidity is not large, and the size change is to meet the size requirement in the actual engineering. In practical engineering application, the applicable cross reed units are selected according to the required deformation range and deformation mode and the stress condition of the actual whole bending mechanism, and due to the fact that the rigidity and deformation mode of different units are different, the multi-stage passive bending deformation mechanism can carry out complex bending deformation, for example, S-shaped deformation can be generated, or the combination mode of the cross reed units is designed, so that the required complex deformation mode can be achieved.

The cambered surface free end that this scheme adopted to the intersection point of crossing reed overlaps with the unit of crossing reed for the centre of a circle of the outside free end of whole bending mechanism, and this makes the offset of crossing point decline to some extent when every crossing reed unit is moved bending deformation, makes its deformation accuracy higher. When the free end is subjected to external force, the free end is better deformed along the stress direction.

The installation and use processes of the invention are as follows:

according to the size of the required multistage bending mechanism and the requirement of the bending form, a proper combination of crossed reed units is selected, the crossed reed units are connected in sequence in the selected sequence in a gluing mode, namely, the free ends of the upper stage of the lower stage are connected, so that the multistage passive bending mechanism formed by combining a set of established crossed reed units is formed, and corresponding bending deformation is generated under the condition of external force. As shown in fig. 2, the passive bending mechanism is mainly concentrated on the free end of each cross reed at the position where the external force is applied, and the free end at the left side of the No. 6 cross reed unit is fixed, in fig. 2, the force direction of all the free ends is assumed to be downward, so that the passive bending moment of each stage of cross reeds is shown in fig. 2. In fig. 3, all the free ends have a downward bending tendency if they are forced downward, and have an upward bending tendency if they are forced upward. In practical situations, the free ends of the cross reeds are stressed differently, so that the passive bending tendency of each stage is different, but the bending performance of the cross reeds can be controlled, so that the multi-stage passive bending mechanism can form more complex and controllable bending deformation.

Claims

1. A multi-stage passive bending mechanism based on cross reeds with variable cross sections is characterized by comprising a plurality of cambered free ends and cross reeds with variable cross sections; two equal-length reeds with variable cross sections are symmetrically and alternately connected with two adjacent cambered free ends along the length direction of the reeds to form a first stage, the cross section of each reed is thinnest at the intersection point, and is thickest at the part connected with the free ends; the rigidity of each bending stage depends on the material and thickness of the reeds, the included angle of the two reeds and the position of the intersection point of the two reeds; the rigidity of the reeds is in direct proportion to the strength of materials, the thickness of the reeds, the included angle of the two reeds and the length proportion of the reeds on two sides of the intersection point of the two reeds, namely the ratio of the length of one side with small length to the length of one side with large length, and the rigidity of the multistage reeds is sequentially reduced from the first-stage reeds to the last stage, so that the bending deformation of the tip which is closer to the bending structure is larger when the external force is applied to the multistage reeds to generate passive deformation.

2. The multi-stage passive bending mechanism based on variable cross-section cross-spring as claimed in claim 1, wherein: two equal-length variable-section reeds are symmetrically and alternately connected with two adjacent cambered free ends along the length direction of the reeds to form a crossed reed unit, and a plurality of crossed reed units are connected in series to form a multi-stage passive bending mechanism.

3. The multi-stage passive bending mechanism based on variable cross-section cross reed according to claim 1 or 2, wherein: the rigidity of the multi-stage reeds is kept to be the maximum when the rigidity of the first stage of reeds is kept, and other stages of reeds are combined according to the required rigidity on the material and the thickness of the reeds, the included angle of the two reeds and the position of the intersection point of the two reeds.

4. The multi-stage passive bending mechanism based on variable cross-section cross reed according to claim 1 or 2, wherein: the size of the free end of the cambered surface is sequentially reduced along the spanwise direction.

5. The multi-stage passive bending mechanism based on variable cross-section cross reed according to claim 1 or 2, wherein: the free ends of the cambered surfaces are in the same bending direction and are bent inwards along the spanwise direction.