Pneumatic rigid-flexible coupling driver and manipulator

Abstract

The pneumatic rigid-flexible coupling driver comprises an extension mechanism and a variable stiffness mechanism, the extension mechanism comprises a first end cover, a second end cover and an extension cavity arranged between the first end cover and the second end cover, and a plurality of rigid ring sleeves arranged at intervals are arranged on the outer circumference of the extension cavity; the variable stiffness mechanism comprises a sleeve mounted on the first end cover and a variable stiffness cavity mounted on the second end cover, and the variable stiffness cavity is inserted into the sleeve; the second end cover is provided with a first air inlet communicated with the extension cavity and a second air inlet communicated with the variable stiffness cavity. When the extension cavity is inflated and expanded, radial expansion of the extension cavity is limited through the discontinuous rigid ring sleeve, and the purpose of achieving the large extension amount under the small air pressure is achieved; and along with the extension of the extension cavity, the variable-stiffness cavity extends out of the sleeve, and real-time variable stiffness of the driver can be realized through inflation expansion of the variable-stiffness cavity, so that the driver has high stiffness and high flexibility.

Description

Technical Field

[0001] The present invention relates to the technical field of manipulators, and in particular to a pneumatic rigid-flexible coupling driver and a manipulator. Background Art

[0002] Traditional rigid manipulators have the advantages of strong load capacity and high control accuracy. Although they are widely used, they often require high-precision sensing and complex control. Their inherent high rigidity also limits their flexibility, making them prone to damage to fragile objects when performing grasping tasks. Since soft robots have the advantages of good flexibility and good environmental interactivity, soft manipulators have come into being. As an important part of the robot system, soft manipulators have been widely used in various occasions. For example, fruit grasping, underwater grasping, minimally invasive surgery, etc.

[0003] As an important component of soft manipulators, soft actuators have been widely studied by scholars in recent years. At present, scholars have developed a variety of soft actuators with different driving modes, and their driving modes can be summarized as linear drive, pneumatic drive, shape memory material drive and dielectric elastomer drive. Among them, pneumatic drive has become one of the most commonly used methods because it is easy to control and adjust. By inflating the internal inflatable cavity of the soft actuator made of soft materials, the soft actuator can exhibit different deformations and movements. However, since the current soft actuators are all pure flexible devices and the inherent low stiffness characteristics of soft materials, they cannot grasp heavy objects when performing grasping tasks and are easily disturbed by external forces. Therefore, many scholars have carried out research on variable stiffness devices for soft actuators.

[0004] At present, there are two main types of research on variable stiffness of soft actuators. The first type is embedded low-melting-point alloys or polymers. The structure of this type of actuator is similar to the typical pneumatic network structure. The outer layer is a bending and deforming driving layer, and the inner layer is replaced by the original inextensible layer with an inner skeleton layer containing low-melting-point alloys or polymers. Although this type of actuator has good stiffness adjustment ability, its biggest drawback is that the response time is too long. The second type is to use interference structures, among which the most widely used are particle interference and interlayer interference. The particle interference form mainly extracts vacuum from the film wrapped with stacked particles (such as coffee beans, rice, etc.) to squeeze the internal particles against each other, thereby hardening and improving the stiffness of the flexible actuator, but this method has the disadvantages of large weight and difficulty in recovery after deformation. The interlayer interference form has a similar working principle to the particle interference form, which mainly extracts vacuum from the film wrapped with a stacked structure (such as A4 paper, sandpaper, etc.) to increase the friction between the stacked structures and thus improve the overall stiffness. However, most of the variable stiffness methods based on the interference principle require negative pressure for vacuum clamping, which requires an additional negative pressure gas source, increasing the cost of use and making the control complicated. In addition, the interlayer interference shape adaptability is poor, and it is usually used for the variable stiffness of soft bending actuators. Particle interference will produce a hollow area after elongation, affecting the global variable stiffness. Therefore, it is necessary to study a new type of actuator. Summary of the invention

[0005] The present invention provides a pneumatic rigid-flexible coupling driver and a manipulator to solve the above technical problems.

[0006] In order to solve the above technical problems, the present invention provides a pneumatic rigid-flexible coupling driver, including an extension mechanism and a variable stiffness mechanism, the extension mechanism includes a first end cover, a second end cover and an extension cavity arranged between the first end cover and the second end cover, and a plurality of rigid ring sleeves arranged at intervals are provided on the outer circumference of the extension cavity; the variable stiffness mechanism includes a sleeve installed on the first end cover, and a variable stiffness cavity installed on the second end cover, and the variable stiffness cavity is inserted into the sleeve; the second end cover is provided with a first air inlet connected to the extension cavity, and a second air inlet connected to the variable stiffness cavity.

[0007] Preferably, a plurality of annular grooves are provided on the outer circumference of the elongated cavity, and the rigid ring sleeve is confined in the annular grooves.

[0008] Preferably, the first end cover, the second end cover, the rigid ring sleeve and the sleeve are made of polylactic acid or metal material.

[0009] Preferably, the first end cover, the second end cover, the rigid ring sleeve and the sleeve are made by 3D printing technology.

[0010] Preferably, the elongated cavity and the variable stiffness cavity are made of silicone or thermoplastic polyurethane material.

[0011] Preferably, the relationship between the elongation ΔL of the pneumatic rigid-flexible coupling actuator and the air pressure P1 in the elongation cavity is:

[0012]

[0013] Where L is the length of the elongated cavity before deformation, D is the outer diameter of the elongated cavity, d1 is the inner diameter of the elongated cavity before deformation, C 10 and C 01 All are material coefficients.

[0014] The present invention also provides a robot arm, comprising two groups of grasping fingers symmetrically mounted on a fixed plate, each group of grasping fingers comprising a sliding rod, a slider, a connecting rod, a grasping end and the pneumatic rigid-flexible coupling driver as described above, one end of the pneumatic rigid-flexible coupling driver being fixed to the fixed plate, and the other end being slidably mounted on the sliding rod through the slider; one end of the sliding rod being fixed to the fixed plate, and the other end being hinged to a first connection point of the grasping end, and the bottom of the pneumatic rigid-flexible coupling driver being hinged to a second connection point of the grasping end through a connecting rod.

[0015] Preferably, a plurality of contact cavities are fixed on the gripping surface of the gripping end, and a third air inlet is provided on the contact cavity.

[0016] Preferably, at least one sensor is installed on the contact cavity.

[0017] Preferably, the rotating shafts at the hinges between the bottom of the pneumatic rigid-flexible coupling actuator and the connecting rod, between the connecting rod and the second connecting point, and between the sliding rod and the second connecting point are all made of stainless steel plug screws.

[0018] Compared with the prior art, the pneumatic rigid-flexible coupling actuator and the manipulator provided by the present invention have the following advantages:

[0019] 1. In the present invention, when the elongation cavity is inflated, the radial expansion of the elongation cavity is limited by a discontinuous rigid ring sleeve, so that a larger elongation amount can be achieved under a smaller air pressure; and as the elongation cavity is extended, the variable stiffness cavity extends from the sleeve, and the variable stiffness cavity is inflated to achieve real-time variable stiffness of the driver, so that the driver effectively combines the high stiffness of the rigid component and the high compliance of the flexible component;

[0020] 2. The present invention only needs a positive pressure gas source in both the elongated state and the variable stiffness state, that is, the positive pressure is used for driving and variable stiffness, which saves the use cost and is simple to control;

[0021] 3. The manipulator provided by the present invention can achieve stable grasping of objects of different shapes and weights, and can be used in a variety of situations where fragile objects of different shapes and weights need to be grasped. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the structure of a pneumatic rigid-flexible coupling actuator in a specific embodiment of the present invention;

[0023] Figure 2 A cross-sectional view of a pneumatic rigid-flexible coupling actuator in a specific embodiment of the present invention;

[0024] Figure 3 It is a schematic diagram of the elongated state of the pneumatic rigid-flexible coupling actuator in a specific embodiment of the present invention;

[0025] Figures 4a to 4c It is a schematic diagram of the structural changes of the variable stiffness mechanism in three states in a specific embodiment of the present invention;

[0026] Figure 5 It is a schematic diagram of theoretical modeling of an elongation mechanism in a specific embodiment of the present invention;

[0027] Figure 6 A schematic diagram of theoretical modeling of a variable stiffness mechanism in a specific embodiment of the present invention;

[0028] Figure 7 It is a schematic diagram of the air pressure-elongation experimental results of the pneumatic rigid-flexible coupling actuator in a specific embodiment of the present invention;

[0029] Figure 8 It is a schematic diagram of the stiffness test results of a pneumatic rigid-flexible coupling actuator in a specific embodiment of the present invention;

[0030] Fig. 9 It is a structural schematic diagram of a manipulator in a specific embodiment of the present invention;

[0031] Fig.10 It is a schematic diagram of the pull-off force test results of the manipulator in a specific embodiment of the present invention;

[0032] Fig.11 It is a schematic diagram of a manipulator grasping different objects in a specific embodiment of the present invention.

[0033] In the figure: 100-pneumatic rigid-flexible coupling actuator, 10-first end cover, 20-second end cover, 21-first air inlet, 22-second air inlet, 30-elongated cavity, 31-annular groove, 40-rigid ring sleeve, 50-sleeve, 60-variable stiffness cavity;

[0034] 101 -fixed plate, 200 -slide bar, 300 -sliding block, 400 -connecting rod, 500 -grasping end, 501 -first connection point, 502 -second connection point, 600 -contact cavity. DETAILED DESCRIPTION

[0035] In order to describe the technical solution of the above invention in more detail, specific embodiments are listed below to demonstrate the technical effects; it should be emphasized that these embodiments are used to illustrate the present invention but not to limit the scope of the present invention.

[0036] The pneumatic rigid-flexible coupling actuator 100 provided by the present invention is as follows: Figure 1 As shown in Figure 4, it includes an extension mechanism and a variable stiffness mechanism, the extension mechanism includes a first end cover 10, a second end cover 20 and an extension cavity arranged between the first end cover 10 and the second end cover 20, and a plurality of rigid ring sleeves 40 are arranged at intervals on the outer circumference of the extension cavity; the variable stiffness mechanism includes a sleeve 50 installed on the first end cover 10, and a variable stiffness cavity 60 installed on the second end cover 20, the variable stiffness cavity 60 is inserted into the sleeve 50, and the sleeve 50 can be integrally formed with the first end cover 10; the second end cover 20 is provided with a first air inlet 21 connected to the extension cavity 30, and a second air inlet 22 connected to the variable stiffness cavity 60. In the present invention, when air is inflated into the extension cavity 30 through the first air inlet 21, the extension cavity 30 expands, and the radial expansion of the extension cavity 30 is limited by the non-continuous rigid ring sleeve 40, thereby achieving the purpose of achieving a larger axial extension under a smaller air pressure; and as the extension cavity 30 is extended, the variable stiffness cavity 60 extends from the sleeve 50, and air is inflated into the variable stiffness cavity 60 through the second air inlet 22, then the variable stiffness cavity 60 and the sleeve 50 The non-overlapping portion expands, which can realize real-time variable stiffness of the driver, so that the driver effectively combines the high stiffness of the rigid component and the high compliance of the flexible component.

[0037] Specifically, when compressed air enters the extension cavity 30 from the first air inlet 21, the extension cavity 30 will be compressed and expand and deform. Since the rigid ring sleeve 40 limits its radial expansion, the extension cavity 30 will generate axial extension movement under the action of the axial force at the end, such as Figure 3 As shown. When the compressed air in the extension cavity 30 is exhausted, the extension cavity 30 will return to its initial state under the action of its own impedance. The common methods used in existing flexible extension actuators to limit radial deformation include fiber reinforcement, spring constraint and other types. However, the fiber-reinforced constraint layer is easy to fall off under high air pressure, and the spring constraint layer can only achieve a longer extension under high air pressure. The present application uses a non-continuous rigid ring sleeve 40 as a constraint layer. In some embodiments, please continue to refer to Figure 3, a plurality of independent annular grooves 31 are provided on the outer circumference of the elongation cavity 30, and the rigid ring sleeve 40 is limited in the annular grooves 31 to prevent the rigid ring sleeve 40 from sliding during the elongation process and causing instability. Since the annular grooves 31 and the rings of the rigid ring sleeve 40 are independent of each other, the axial elongation of the elongation cavity 30 is not constrained, and a longer elongation can be obtained under a relatively low air pressure. It should be noted that the annular grooves 31 on the outer wall of the elongation cavity 30 should be consistent with the thickness of the rigid ring sleeve 40 to facilitate the positioning of the rigid ring sleeve 40. In the axial direction, the circular shells of the first end cover 10 and the second end cover 20 support and seal the two ends of the elongation cavity 30.

[0038] The rigid-flexible coupling method adopted by the present invention makes full use of the high rigidity of the rigid parts and the high compliance of the flexible parts, and the deformation of the flexible rectangular variable rigidity cavity 60 is predictable and controllable, because the rigid parts (rigid ring sleeve 40 and sleeve 50) limit the expansion of a part of the cavity. When compressed air is filled into the elongation cavity 30 to make it elongate, the variable rigidity mechanism 60 can follow the elongation state of the elongation cavity 30. When the elongation cavity 30 is elongated to a certain length, compressed air is filled into the variable rigidity cavity 60, and the driver enters the variable rigidity state. The initial state of the pneumatic rigid-flexible coupling driver 100 is shown in FIG4(a); the elongation state is shown in FIG4(b), at which time the variable rigidity cavity 60 is not filled with compressed air; when compressed air is filled into the variable rigidity cavity 60, it enters the variable rigidity state, as shown in FIG4(c).

[0039] Due to the restriction of the rigid sleeve 50, the variable rigidity cavity 60 will expand and bulge in the gap, and the remaining variable rigidity cavity 60 that has not bulged will be in close contact with the sleeve 50, thereby increasing the friction between the rigid sleeve 50 and the flexible variable rigidity cavity 60, limiting the relative movement of the two, and achieving a state of enhanced rigidity. The radial direction of the variable rigidity cavity 60 is locked due to the restriction of the sleeve 50; when subjected to a force opposite to the elongation direction in the axial direction, the mechanism will enter a clamping state due to the compression of the expanded variable rigidity cavity 60 by the sleeve 50 and the friction between the sleeve 50 and the unexpanded variable rigidity cavity 60. Therefore, in some embodiments, the first end cover 10, the second end cover 20, the rigid ring sleeve 40 and the sleeve 50 can be made of polylactic acid or metal materials with strong rigidity. The elongation cavity 30 and the variable rigidity cavity 60 can be made of silicone or thermoplastic polyurethane materials, which have strong wear resistance and pressure resistance.

[0040] Since the extension mechanism needs to be combined with the variable stiffness mechanism, the length of the sleeve 50 should be consistent with the length of the extension cavity 30, and its width should avoid contact with the inner side of the extension cavity 30 to prevent affecting the extension effect. Sufficient space should be reserved in height to facilitate the expansion of the variable stiffness cavity 60. Compared with the traditional use of negative pressure to change stiffness, the new positive pressure drive method proposed in the present invention simplifies the control structure and reduces the use cost.

[0041] In order to describe the relationship between the elongation of the actuator and the air pressure under no-load conditions, a mechanical model of the pneumatic rigid-flexible coupling actuator 100 is constructed. Figure 5 As shown, after the actuator is inflated and stretched, it is subjected to the driving force F1 of the air pressure on the end cap and the impedance F2 generated by the stretching cavity 30 itself after stretching and deformation. Assuming that the rigid ring sleeve 40 is tightly matched with the stretching cavity 30 and ignoring the slight influence of the variable stiffness mechanism on it, it can be known from the static balance that: F1 = F2.

[0042] During the inflation and elongation deformation process of the actuator, the inner wall of the elongation cavity 30 will become thinner, resulting in a change in the internal cross-sectional area of ​​the elongation cavity 30. Since the material of the elongation cavity 30 is an incompressible superelastic body, the cavity volume remains unchanged before and after the elongation deformation. Assuming that the rigid ring sleeve 40 completely restricts radial expansion, the volume before deformation V1 and the volume after deformation V2 are obtained as follows:

[0043]

[0044] Here, L is the length of the elongation cavity 30 before elongation deformation, and ΔL is the elongation amount. S1 is the cross-sectional area of ​​the outer cavity before deformation, S2 is the cross-sectional area of ​​the inner cavity, and S3 is the cross-sectional area of ​​the inner cavity after deformation, which can be expressed as:

[0045]

[0046] Here D is the outer diameter of the elongated cavity, d1 is the inner diameter of the cavity before elongation, and d2 is the inner diameter of the cavity after elongation. Since V1 = V2, the square of the inner diameter after elongation can be obtained by combining equations (1) and (2): for:

[0047]

[0048] According to the pressure formula, the driving force F1 can be expressed as:

[0049]

[0050] Here P1 is the air pressure in the extension cavity. The driving force F1 is obtained by combining equation (3) with equation (4):

[0051]

[0052] In this embodiment, the elongated cavity 30 is made of silicone material, so the strain energy function is used to express the mechanical properties of the silicone material 30 when expressing the constitutive model of the material. The strain energy density function W represented by the invariants I1, I2 and I3 of the strain tensor is: W = W (I1, I2, I3), where I1, I2 and I3 can be expressed as:

[0053]

[0054] Here, λ1, λ2, and λ3 are respectively the main stretching ratios of the axial, circumferential, and radial directions of the elongation cavity 30. During the elongation process, since the rigid annulus 40 limits the radial expansion of the elongation cavity 30 and the silicone is incompressible, λ1λ2λ3=1, and it can be obtained that:

[0055]

[0056] Combining equation (7) with equation (6), we can get the first two invariants I1 and I2 of the strain tensor as follows:

[0057]

[0058] The Mooney-Rivlin model is used to describe the mechanical properties of silicone. For incompressible materials, its typical binomial parameters can be expressed as:

[0059] W=C 10 (I1-3)+C 01 (I2-3) (9)

[0060] Combining formula (9) with formula (8), we can get:

[0061]

[0062] Here, C 10 and C 01 They all represent material coefficients, and their values ​​can be found in literature.

[0063] The impedance F2 of the elongated cavity 30 itself can be expressed as:

[0064]

[0065] Here σ is the axial stress of the elongated cavity, which can be expressed as:

[0066]

[0067] After the actuator is axially stretched, its axial stretch ratio γ can also be expressed as:

[0068]

[0069] Then the axial stress σ can also be expressed as:

[0070]

[0071] Combining equations (11) and (13), the impedance F2 of the elongated cavity itself is:

[0072]

[0073] Combining equation (14) and equation (4) and simplifying them, the elongation ΔL is:

[0074]

[0075] In addition, since the outer wall of the elongated cavity 30 is provided with an annular groove 31 for mounting the rigid ring sleeve 40, the outer diameter D of the elongated cavity 30 can be expressed as:

[0076]

[0077] Here, D1 is the outer diameter of the annular groove 31 , D2 is the inner diameter of the annular groove 31 , n1 is the number of layers of the outer diameter of the annular groove 31 , and n2 is the number of layers of the inner diameter of the annular groove 31 .

[0078] Specific parameters of the extension cavity 30 are shown in Table 1.

[0079] Table 1 Elongation cavity parameters and specific values

[0080] parameter <![CDATA[C 10 ]]> <![CDATA[C 01 ]]> L <![CDATA[D1]]> <![CDATA[D2]]> <![CDATA[d1]]> <![CDATA[n1]]> <![CDATA[n2]]> Specific value 8.0537kPa 2.0134kPa 52mm 50mm 47mm 36mm 11 10

[0081] In order to explore the stiffness characteristics of the variable stiffness mechanism, the stiffness of the mechanism is expressed from the perspective of energy. It is assumed that the work done by the external force is completely converted into the elastic strain energy of the variable stiffness cavity 60 and the friction heat energy between the cavity and the sleeve 50, that is:

[0082] W F =W f +U (16)

[0083] Here W F is the work done by the air pressure, W f is the friction heat energy, and U is the elastic strain energy of the variable stiffness cavity 60. According to formula (16), the greater the friction heat energy, the smaller the elastic strain energy, that is, the higher the stiffness of the variable stiffness mechanism. Therefore, the friction heat energy W f It can be expressed as:

[0084] W f =fx (17)

[0085] Here, f is the friction force between the variable stiffness cavity 60 and the sleeve 50, and x is the sliding displacement between the variable stiffness cavity 60 and the sleeve 50. f can be expressed as:

[0086] f=μF N =μP2s (18)

[0087] Here μ is the friction coefficient, F N is the normal force between the variable stiffness cavity 60 and the sleeve 50, P2 is the air pressure in the variable stiffness cavity 60, and s is the contact area between the variable stiffness cavity 60 and the sleeve 50, which can be expressed as:

[0088] s=2d(l1-l2) (19)

[0089] Here d and l1 are the width and length of the variable stiffness cavity (excluding wall thickness), and l2 is the elongation length, such as Figure 6 As shown, the friction heat energy W can be obtained f for:

[0090] W f =2xμP2d(l1-l2) (20)

[0091] According to formula (20), the stiffness of the variable stiffness mechanism is related to the friction coefficient μ between the variable stiffness cavity 60 and the sleeve 50, the air pressure P2 in the variable stiffness cavity 60, and the extension length l2.

[0092] In this embodiment, the elongated cavity 30 is made of Ecoflex 0030 silicone material, which has a Shore hardness of 00-30 and good flexibility, and can meet the use requirements.

[0093] The elongated cavity 30 can be molded by casting. In order to facilitate demoulding, the mold for making the elongated cavity 30 can be divided into three parts, including two symmetrical outer molds with grooves and a smooth cylindrical inner mold with a base. In the manufacturing process, the three molds are first assembled, and after the assembly is completed, liquid silicone is slowly poured through the top gap. After the liquid silicone is cured, the two symmetrical outer molds are first separated, and then the elongated cavity 30 is pulled out of the inner mold and the rigid ring sleeve 40 is installed. At this point, the elongated cavity 30 constrained by the rigid ring sleeve 40 is completed.

[0094] The variable stiffness cavity 60 is made of a silicone material with a relatively high hardness, and can also be made by casting. If the hardness of the silicone used is relatively low, the variable stiffness performance will deteriorate. If the hardness of the silicone used is too high, it will not be easy to demold. Therefore, this embodiment uses a translucent silicone material with a hardness of 30 degrees produced by Shenzhen Preston Silicone Material Co., Ltd. The silicone has a high hardness and is easy to demold. The production of the columnar tube of the variable stiffness cavity 60 can also divide the mold into two parts, an outer mold and an inner mold. After the mold is assembled, pour liquid silicone into it. After curing, separate the mold and pull the cavity out of the mold; then make a plate-shaped head, and bond the two with silicone. At this point, the variable stiffness cavity 60 is completed.

[0095] It should be noted that after the mold is assembled, solder mask should be applied on the surface of the gap to fix the mold and prevent the liquid silicone from leaking. When separating the mold, the solidified solder mask should be peeled off first. Before pouring the liquid silicone, a vacuum device should be used to remove the bubbles in the liquid silicone and vaseline lubricant should be evenly applied on the inner surface of the mold. After obtaining the elongated cavity 30 and the variable stiffness cavity 60 constrained by the rigid ring sleeve 40, the first end cover 10, the second end cover 20 and the sleeve 50 can be made by 3D printing technology, and the various parts are bonded with glue. At this point, the pneumatic rigid-flexible coupling actuator 100 is completed.

[0096] In order to obtain the relationship between the inflation pressure and elongation of the pneumatic rigid-flexible coupling actuator 100, a pneumatic rigid-flexible coupling actuator 100 was selected for an air pressure-elongation experiment. First, an experimental platform was built, one end of the actuator was fixed to the bracket, and the bracket was clamped with a clamp. After inflating from the first air inlet 21 to make the actuator axially elongate, its elongation was measured. This experiment uses an air compressor as the air source, with an air source processor to provide a stable air supply, and connects a pneumatic pressure regulating valve with an air pressure sensor to accurately control the air pressure.

[0097] During the experiment, the inflation pressure in the elongation cavity 30 was increased from 0 to 20 kPa in increments of 2 kPa, and the elongation change was recorded every 2 kPa, while the pressure in the variable stiffness cavity 60 was always kept at 0. Finally, the theoretical data was compared with the measured experimental data to obtain a curve of elongation and inflation pressure. Figure 7 As shown in the figure, it can be seen that with the increase of the air pressure in the elongation cavity 30, the elongation of the driver increases nonlinearly, and the changing trend of the experimental data is consistent with the changing trend of the theoretical data, and the agreement is good, indicating that the established air pressure-elongation theoretical model can truly reflect the elongation of the driver under different air pressures.

[0098] In order to test the variable stiffness performance of the actuator, an experimental platform was built, one end of the extended actuator was fixed on the bracket, and the bracket was clamped with a clamp, and then 500g, 1000g and 1500g weights were placed vertically on the other end. In order to test the change in stiffness of the actuator under different elongations, the air pressure in the elongation cavity 30 corresponding to each set of weights was 10kpa, 15kpa and 20kpa respectively. In the experiment, the air pressure in the variable stiffness cavity 60 increased from 0 to 50kpa in increments of 5kpa, and the displacement was recorded every 5kPa. After each displacement measurement, the air pressure in all cavities was discharged, and after it returned to the initial state, it was refilled with different air pressures to measure the experimental data. Among them, 0kpa is the state before the actuator changes stiffness, and its stiffness change is measured by measuring the displacement change of the actuator under different weights and different elongations.

[0099] The displacement curve of the actuator before and after the stiffness change is plotted. Figure 8 As shown in the figure, the displacement change curves under 500g, 1000g and 1500g weights are respectively shown. The experimental results show that when the variable stiffness cavity 60 is not inflated, as the air pressure in the elongation cavity 30 increases, the displacement of the driver after the weight is placed gradually increases, which means that the stiffness is gradually decreasing. However, as the air pressure in the variable stiffness cavity 60 increases, the displacement of the driver gradually decreases, which means that the stiffness is gradually increasing. As the elongation increases, this difference is more obvious. It should be noted that when a lower air pressure is filled into the variable stiffness cavity 60, the displacement does not change, mainly because the stiffness increase of the driver is small under this air pressure, which is difficult to offset the load weight, resulting in no change in displacement. In short, the experimental phenomenon is consistent with the theoretical analysis of formula (20).

[0100] Based on the above-mentioned pneumatic rigid-flexible coupling actuator 100, the present invention also provides a manipulator, including two groups of grasping fingers symmetrically mounted on a fixed plate 101, each group of grasping fingers including a slide bar 200, a slider 300, a connecting rod 400, a grasping end 500 and the above-mentioned pneumatic rigid-flexible coupling actuator 100, one end (the first end cover 10 or the second end cover 20) of the pneumatic rigid-flexible coupling actuator 100 is fixed on the fixed plate 101, and the other end (the second end cover 20 or the first end cover 10) is slidably mounted on the slide bar 200 through the slider 300; one end of the slide bar 200 is fixed on the fixed plate 101, and the other end is hinged to the first connection point 501 of the grasping end 500, the bottom of the pneumatic rigid-flexible coupling actuator 100 is hinged to the second connection point 502 of the grasping end 500 through the connecting rod 400, and each component can also be made of 3D printed PLA plastic. In order to ensure the stability of the overall structure, stainless steel screws can be used to fix the parts. When compressed air is filled into the extension cavity 30, the extension motion of the driver is converted into a bending motion of the gripping end 500 through the connecting rod 400. The prototype of the manipulator assembled by fixing two gripping fingers by the fixing plate 101 is shown in FIG. Fig. 9 As shown. The traditional two-finger flexible manipulator often has insufficient load-bearing capacity due to insufficient output force or lack of variable stiffness capability. The manipulator designed by the present invention is driven by a flexible driver with variable stiffness capability. In terms of force, the rigid part will serve as one of the force-bearing components, with a higher upper limit of load, which effectively improves the grasping ability.

[0101] In some embodiments, please refer to Fig. 9, a plurality of contact cavities 600 are fixed on the gripping surface of the gripping end 500, and a third air inlet (not shown) is provided on the contact cavity 600. When grasping an object, the contact area between the object and the contact surface is a key factor. The larger the contact area, the more stable the object. In order to further improve the gripping performance of the manipulator of the present application, the present application fixes a contact cavity 600 made of silicone (with a hardness of 10 degrees) on the gripping end 500. In the present embodiment, four contact cavities 600 are fixed at the end of each manipulator, and air is supplied by an air pipe. After grasping the object, air is supplied to the contact cavity 600, and the contact cavity 600 will expand and wrap the object to increase the contact area with the object during grasping.

[0102] In order to test the influence of the stiffness adjustment mechanism of the actuator on the load-bearing capacity of the manipulator, a pull-off force experiment was conducted. The pull-off force is the peak force required to pull the object out of the manipulator. When pulling the object out of the grasping state, a force opposite to the elongation direction is applied to the actuator, that is, the greater the stiffness of the actuator, the greater the force to pull the object out of the manipulator. For example, the manipulator grasps a 3D printed PLA material 65mm diameter ball and pulls it vertically downward. The digital force sensor is mounted on a linear guide rail, moves vertically downward and records the maximum value during the process.

[0103] During the experiment, the elongation cavity 30 was filled with 12kpa, 15kpa and 18kpa air pressures respectively, and then the variable stiffness cavity 60 was filled with different air pressures. After the stiffness was enhanced, the contact cavity 600 at the end was filled with 5kpa air pressure to wrap the ball to improve stability. The air pressure in the variable stiffness cavity 60 increased from 0 to 50kpa in increments of 10kpa, and the force data was recorded every 10kPa. After each force data measurement, the air pressure in all cavities was discharged, and after it returned to the initial state, it was refilled with different air pressures to measure the experimental data. Three groups of pull-off force tests were conducted, and each group of experiments was repeated three times. The experimental results were averaged as shown in the figure. Fig.10 shown.

[0104] The experimental results show that the pull-off force after changing the stiffness is about 3 times, 1.9 times, and 1.6 times greater than that before changing the stiffness, respectively. This is because the stiffness of the driver is enhanced after the variable stiffness cavity 60 is inflated, enabling it to resist the reaction force generated when the object is pulled off.

[0105] Theoretically, when the diameter of the grasped object is different, the carrying capacity of the manipulator is also different. From the stiffness experiment of the aforementioned pneumatic rigid-flexible coupling actuator 100, it can be seen that as the elongation length increases, the stiffness of the actuator gradually decreases, that is, the larger the bending angle of the manipulator, the lower its carrying capacity. In order to test the maximum carrying capacity of the manipulator, a pull-off force test was carried out at the maximum grasping diameter. The above-mentioned 65mm diameter ball was replaced with a 100mm diameter ball, and the elongation cavity 30, the variable stiffness cavity 60 and the contact cavity 600 at the end were filled with 30kPa, 50kPa and 15kPa air pressures respectively. The three experimental results and the average values ​​are shown in Table 2. The experimental results show that the maximum load-bearing weight of the manipulator is 60.3N.

[0106] Table 2 Maximum load-bearing weight test results

[0107]

[0108] For heavy objects, ordinary flexible manipulators cannot successfully grasp them due to lack of variable stiffness capability. The manipulator provided in this application can adjust the stiffness of the driver by changing the gas pressure input in the variable stiffness cavity 60 to improve the load capacity of the manipulator, that is, the manipulator can achieve the task of grasping heavy objects.

[0109] Taking grabbing a 1000g weight as an example, the extension cavity 30 is filled with 20kPa air pressure to clamp the weight, and after grabbing, the contact cavity 600 is filled with 8kPa air pressure. Without adjusting the stiffness, the manipulator falls after grabbing due to its own insufficient load performance.

[0110] The same 20kPa air pressure is filled into the extension cavity 30, and then 50kPa air pressure is filled into the variable stiffness cavity 60, and the same 8kPa air pressure is filled into the contact cavity 600 after grasping. At this time, the driver enters the stiffness enhancement state, the carrying capacity of the manipulator is improved, and the weight is grasped successfully and stably.

[0111] The above experimental results show that thanks to the stiffness adjustment capability of the variable stiffness mechanism, the stiffness of the driver is enhanced, and thus the carrying capacity of the manipulator is improved.

[0112] The present invention also conducted a series of grasping experiments to verify the grasping ability of the manipulator provided in this application. Common objects in daily life were selected for grasping experiments. For all objects, the grasping steps are the same. First, the extension cavity 30 is inflated to extend the driver, driving the grasping end 500 to bend to the size of the target object. At this time, the variable stiffness cavity 60 is inflated to increase the stiffness of the driver, thereby increasing the carrying capacity of the manipulator. Finally, the contact cavity 600 at the end is inflated to increase the contact area with the object and improve the grasping stability. After the grasping is completed, the air pressure in the end contact cavity 600 is first released, then the air pressure in the variable stiffness cavity 60 is released, and finally the air pressure in the extension cavity 30 is released to return to the initial state. Fig.11 As shown, the present application grasped a wide variety of items, including 188.1g of tomatoes, 86.4g of kiwis, 194.4g of star fruits, 47.9g of eggs, 70g of bread, 77.2g of steamed buns, 574.4g of mineral water, 214.2g of pliers, 414.9g of perfume, 82.6g of Rubik's Cube, 375.1g of pressure gauge, and 62.5g of hexagonal prism.

[0113] The experimental results show that, thanks to the flexibility of the actuator, the surfaces of all objects are not damaged after the grasping. In particular, thanks to the adjustable stiffness of the actuator and the fit of the end contact cavity 600 to the object, all objects can be grasped stably during the grasping process without tilting left or right or even falling.

[0114] In some embodiments, the rotating shafts at the hinges between the bottom of the pneumatic rigid-flexible coupling actuator 100 and the connecting rod 400, the connecting rod 400 and the second connection point 502, and the sliding rod 200 and the first connection point 501 are all made of stainless steel plug screws. Since the surface of the 3D printed rigid shaft is uneven, the friction will increase when rotating. The present application uses stainless steel plug screws with smooth surfaces as the rotating shaft to reduce the friction at the rotating part.

[0115] In some embodiments, at least one sensor (not shown), such as a force sensor, a deformation sensor, a visual sensor, etc., may be installed on the contact cavity 600 to further improve the grasping ability.

[0116] In summary, the pneumatic rigid-flexible coupling actuator and manipulator provided by the present invention include an extension mechanism and a variable stiffness mechanism, the extension mechanism includes a first end cover 10, a second end cover 20 and an extension cavity arranged between the first end cover 10 and the second end cover 20, and a plurality of rigid ring sleeves 40 arranged at intervals are provided on the outer circumference of the extension cavity; the variable stiffness mechanism includes a sleeve 50 installed on the first end cover 10, and a variable stiffness cavity 60 installed on the second end cover 20, and the variable stiffness cavity 60 is inserted into the sleeve 50; the second end cover 20 is provided with a first air inlet 21 connected to the extension cavity 30, and a second air inlet 22 connected to the variable stiffness cavity 60. The present invention adopts a rigid-flexible coupling method to combine a rigid part consisting of a rigid end cover, a sleeve 50 and a rigid ring sleeve 40 with a soft rectangular variable stiffness cavity 60 and a soft cylindrical elongation cavity 30 constrained by the rigid ring sleeve 40, thereby maintaining its high elongation flexibility while also having variable stiffness capability.

[0117] Obviously, those skilled in the art can make various changes and modifications to the invention without departing from the spirit and scope of the invention. Thus, if these modifications and variations of the invention fall within the scope of the claims of the invention and their equivalents, the invention is also intended to include these modifications and variations.

Claims

1. A pneumatic rigid-flexible coupling actuator, characterized in that: It includes an extension mechanism and a variable stiffness mechanism, the extension mechanism includes a first end cover, a second end cover and an extension cavity arranged between the first end cover and the second end cover, and a plurality of rigid ring sleeves arranged at intervals are provided on the outer circumference of the extension cavity; the variable stiffness mechanism includes a sleeve installed on the first end cover, and a variable stiffness cavity installed on the second end cover, and the variable stiffness cavity is inserted into the sleeve; the second end cover is provided with a first air inlet connected to the extension cavity, and a second air inlet connected to the variable stiffness cavity.

2. The pneumatic rigid-flexible coupling actuator according to claim 1, characterized in that: A plurality of annular grooves are arranged on the outer circumference of the elongated cavity, and the rigid ring sleeve is confined in the annular grooves.

3. The pneumatic rigid-flexible coupling actuator according to claim 1, characterized in that: The first end cover, the second end cover, the rigid ring sleeve and the sleeve are made of polylactic acid or metal material.

4. The pneumatic rigid-flexible coupling actuator according to claim 1, characterized in that: The first end cover, the second end cover, the rigid ring sleeve and the sleeve are made by 3D printing technology.

5. The pneumatic rigid-flexible coupling actuator according to claim 1, characterized in that: The elongated cavity and the variable rigidity cavity are made of silicone or thermoplastic polyurethane material.

6. The pneumatic rigid-flexible coupling actuator according to claim 1, characterized in that: The relationship between the elongation ΔL of the pneumatic rigid-flexible coupling actuator and the air pressure P1 in the elongation cavity is: Where L is the length of the elongated cavity before deformation, D is the outer diameter of the elongated cavity, d1 is the inner diameter of the elongated cavity before deformation, C 10 and C 01 All are material coefficients.

7. A robot, characterized in that: It comprises two groups of gripping fingers symmetrically mounted on a fixed plate, each group of the gripping fingers comprises a sliding rod, a slider, a connecting rod, a gripping end and the pneumatic rigid-flexible coupling actuator as claimed in claim 1, one end of the pneumatic rigid-flexible coupling actuator is fixed to the fixed plate, and the other end is slidably mounted on the sliding rod through the slider; one end of the sliding rod is fixed to the fixed plate, and the other end is hinged to the first connection point of the gripping end, and the bottom of the pneumatic rigid-flexible coupling actuator is hinged to the second connection point of the gripping end through a connecting rod.

8. The robot according to claim 7, characterized in that: A plurality of contact cavities are fixed on the gripping surface of the gripping end, and a third air inlet is opened on the contact cavity.

9. The robot according to claim 8, characterized in that: At least one sensor is installed on the contact cavity.

10. The robot according to claim 7, characterized in that: The rotating shafts at the hinges between the bottom of the pneumatic rigid-flexible coupling driver and the connecting rod, between the connecting rod and the second connecting point, and between the sliding rod and the second connecting point are all made of stainless steel plug screws.

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