Electro-hydraulic buoyancy adjustment drive

Abstract

The application discloses an electro-hydraulic buoyancy adjusting driver, which comprises a shell, electrodes, a dielectric film capsule and dielectric liquid, and is driven by a power supply control module; the dielectric film capsule is divided into two parts, i.e. an inner capsule sealed in the shell and an outer capsule exposed to water and capable of freely deforming; the dielectric film capsule is filled with the dielectric liquid; the upper surface and the lower surface of the inner capsule are covered with the electrodes, and the electrodes are connected with the power supply control module. The electro-hydraulic buoyancy adjusting driver provided by the application can control the adsorption process of the electro-hydraulic driver and the size of the buoyancy of the driver by changing the shell gap and the overall volume change of the driver during the driving process.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of underwater buoyancy adjustment device, and particularly relates to an electro-hydraulic buoyancy adjustment driver. BACKGROUND

[0002] One of the important functional components of underwater robots is the depth adjustment system. Compared with providing vertical propulsion, changing the buoyancy to achieve depth control is a more stable and energy-saving method. However, the hydrostatic load in the volume change process is different from the linear load commonly seen in flexible functional materials. The deformation behavior of the electro-responsive driver under the coupling action of hydrostatic pressure and electric excitation needs further study.

[0003] The flexible electro-hydraulic actuators provided in the prior art are consistent with the dielectric elastomer driven by Maxwell stress, and its prototype is similar to the balloon type DE actuator, except that the flexible electro-hydraulic actuator directly generates pressure through Maxwell stress, rather than changing the DE film tension to change the pressure. In 2018, Acome et al. published an article in Science, which first named this type of actuator as a hydraulically amplified self-healing electrostatic actuator (HASEL actuator) (Acome, E. et al. Hydraulically amplified self-healing electrostatic actuators with muscle-like performance. Science 359, 61-65 (2018)). Initially, the HASEL actuator utilizes an elastic DE film to wrap the liquid for driving, which has the advantage of self-repairing after electrical breakdown compared with using DE alone, however, using an elastic DE film means that part of the output energy of the power supply will still be converted into the strain energy of the elastic film, and the selection of elastic DE film that meets the demand of electrical performance is limited, so that the thermoplastic dielectric film that has been commercially used in film capacitors enters the researchers' field of vision. Inspired by the Peano actuator designed by Niiyama and Sanan et al., Kellaris et al. designed a Peano-HASEL actuator using a biaxially oriented polypropylene (BOPP) thermoplastic film (Kellaris, Nicholas, et al. "Peano-HASEL actuators: Muscle-mimetic, electrohydraulic transducers that linearly contract on activation." Science Robotics 3.14 (2018): eaar3276.), which does not require pre-stretching, does not require a rigid frame, and can achieve a controllable linear contraction strain of 10% and a strain rate of 900% per second at a driving frequency of 50Hz, which makes the Peano-HASEL actuator a very potential electrically responsive flexible actuator.

[0004] Specifically, the flexible electro-hydrostatic actuator (HASEL) has the advantages of high energy efficiency, fast response and low noise. However, the HASEL actuator achieves driving by changing shape rather than volume, which means that it cannot provide buoyancy control in underwater applications itself. At the same time, the hydrostatic pressure is different from the linear load, and the performance of the actuator cannot be described by the traditional Peano-HASEL model. Therefore, when the flexible electro-hydrostatic actuator is used in underwater applications, the mechanical model and structural design for the hydrostatic load need to be implemented to achieve buoyancy adjustment.

[0005] On the other hand, the pre-inflated dielectric elastomer actuator achieves depth control through a swim bladder-like buoyancy adjustment mechanism. However, the nonlinear relationship between Maxwell stress and electric field intensity makes it difficult for such actuators to achieve efficient buoyancy adjustment at low voltage, while at high voltage, the buoyancy changes too much with voltage and is difficult to control. The driving performance of the DE actuator can be enhanced by using a magnet, and the nonlinear force-displacement relationship of the magnet can be used to achieve snap-through, bistability and other characteristics. However, when used in water, there is a hydrostatic pressure coupling effect, and the mechanical model for regulating the magnet snap-through and achieving multi-stage buoyancy adjustment still needs further research. SUMMARY

[0006] The purpose of the present application is to provide an electro-hydrostatic buoyancy adjustment actuator that uses the change in the overall volume of the actuator during driving to control the adsorption process of the electro-hydrostatic actuator by changing the gap between the shells, thereby controlling the buoyancy of the actuator.

[0007] The present application provides the following technical solutions:

[0008] An electro-hydrostatic buoyancy adjustment actuator, the actuator comprising a shell, electrodes, a dielectric film capsule, and dielectric liquid, the actuator being driven by a power supply control module;

[0009] The dielectric film capsule is divided into two parts: an inner capsule sealed in the shell and an outer capsule exposed to water and free to deform; the dielectric film capsule contains dielectric liquid;

[0010] The upper and lower surfaces of the inner capsule are covered with electrodes, and the electrodes are connected to the positive and negative electrodes of the power supply control module.

[0011] The dielectric film capsule containing dielectric liquid is the driving body; the electrodes on the upper and lower surfaces of the inner capsule are connected to the positive and negative electrodes of the power supply control module, respectively; the inner capsule is sealed in the shell by sealing glue.

[0012] When the actuator is placed in water in an un-driven state / no voltage loading, the volume of the outer capsule decreases due to the hydrostatic pressure, and the inner capsule expands until the air pressure inside the shell is equal to the hydrostatic pressure outside the shell.

[0013] Further, the shell not only isolates the inner capsule from water, but also limits its deformation.

[0014] When in the driving state / when the voltage is applied, the volume of the inner capsule decreases until the force balance between the Maxwell stress, the air pressure and the hydrostatic pressure is reached.

[0015] Specifically, when the voltage is applied, the Maxwell stress causes the two layers of dielectric films of the inner capsule to be attracted together, and this process starts from the area where the two layers of dielectric films are closest to each other and gradually extends to the area where the two layers of dielectric films are farther apart, like a zipper. During this process, the liquid in the attracted area is gradually squeezed into the outer capsule, the volume of the inner capsule decreases, and until the force balance between the Maxwell stress, the air pressure and the hydrostatic pressure is reached.

[0016] Further, assuming that the dielectric liquid is incompressible, i.e., the volume changes of the inner capsule and the outer capsule are consistent, and the shell is a rigid constraint, i.e., the space in the shell is fixed. At this time, the volume of the outer capsule determines the total volume of the electro-hydraulic buoyancy adjustment driver. When the voltage increases, the volume of the outer capsule increases, the overall volume becomes larger, a positive buoyancy is generated, and the driver floats up; on the contrary, when the voltage decreases, the volume of the outer capsule decreases, the overall volume of the driver becomes smaller, a negative buoyancy is generated, and the driver sinks.

[0017] Further, the length of the inner capsule in the l direction is less than the length in the b direction, the l direction is the length of the attracted area, and the b direction is the width of the attracted area; the total amount of dielectric liquid filled in the dielectric film capsule is not more than the maximum volume of the outer capsule.

[0018] The maximum attraction distance is limited by the size of the dielectric liquid capsule and the total amount of dielectric liquid. First, the size of the inner capsule should follow the principle of large width-length ratio, i.e., the length in the l direction is less than the length in the b direction to ensure that the deformation in the bag is a cylinder, not a sphere. Second, the total amount of dielectric liquid filled in the dielectric liquid capsule should not exceed the maximum volume of the outer capsule (i.e., the volume when it is deformed into a cylinder), otherwise the pressure in the dielectric liquid capsule during driving may be higher than the external hydrostatic pressure, resulting in failure of the dielectric film packaging.

[0019] The present application also provides a control equation of an electro-hydraulic buoyancy adjustment driver, including the following contents:

[0020] The control equation of the electro-hydraulic buoyancy adjustment driver under rigid constraint is established by the minimum energy principle. First, three assumptions in the model need to be explained. First, the dielectric film and the dielectric liquid are assumed to be ideal, i.e., both are incompressible materials, and the dielectric constant does not change with the electric field. Second, the dielectric film is assumed to be inextensible. Third, the gravitational potential energy of the dielectric liquid is ignored, and the change of the static electric energy stored in the un-attracted area is not considered.

[0021] When the system is in the equilibrium state, the change of the total free energy is represented as:

[0022] δU w + δU a + δU p + δU e = 0 (1)

[0023] where δU w and δU a are the potential energy changes of water and air, respectively, δU p is the electrical energy change of the constant voltage source, and δU e is the electrical energy change stored in the adsorption region as a capacitor.

[0024] Since the deformation energy of the membrane is neglected, the total free energy change is expressed as:

[0025]

[0026] where δv water is the volume change of the outer capsule, δv air is the volume change of the inner capsule, Φ is the output voltage of the constant voltage source, δc is the capacitance change of the dielectric membrane in the adsorption region, p water is the external hydrostatic pressure, and p air is the gas pressure inside the actuator.

[0027] Considering that the dielectric liquid is incompressible, δv water is equal to δv air , which is denoted as δv in the following; meanwhile, since a constant voltage source is used, the charge change is dependent on the capacitance change δQ = Φδc.

[0028] Further, when the voltage is applied (at the time of actuation), the deformation of the inner capsule is divided into two regions: the adsorption region and the non-adsorption region, with the length of the adsorption region being l (the outer capsule is only considered for volume change and is not concerned about its specific deformation. Due to the effect of hydrostatic pressure, the membrane in the non-adsorption region will adhere to the inner wall, and the part that does not adhere is assumed to maintain the same shape before and after actuation. The deformation shape of the membrane adhering to the inner wall is determined by the shape of the inner wall of the outer shell, which in the two-dimensional case is determined by the gap t d ). The volume change δv and the capacitance change δc are expressed as functions of the length change δl of the adsorption region:

[0029]

[0030] δv = t d bδl (4)

[0031] where ε is the dielectric constant of the dielectric membrane, b and l are the width and length of the adsorption region, respectively, and t f is the thickness of the membrane, t dis the shell gap; by substituting equations (3) and (4) into equation (2), the governing equation becomes:

[0032]

[0033] Here, since both equations (3) and (4) are related to δl, the change of total free energy can be written as a single variable function of δl. It is noted that only before the outer capsule is fully inflated into a cylinder, p water oil .

[0034] Considering the ideal gas law p air = p0v0 / v air and p water = p0+ ρgh, where p0is the atmospheric pressure, ρghis the external liquid pressure, ρ is the external liquid density, h is the external liquid depth, and v0and v air are the initial and current air volume in the shell, respectively, substituting equations (5) into equation (2) gives:

[0035]

[0036] The above equation shows that the equivalent pressure provided by the Maxwell stress is related to the film thickness t f and the shell gap t d , which means that when the applied voltage is able to squeeze out and absorb the dielectric liquid with thickness t d , the absorbed region of the dielectric film will extend forward by δl until the pressure is rebalanced, at which time the total volume change of the actuator becomes t d bδl.

[0037] When the inner wall shape is artificially designed, the relationship between the shell gap and l satisfies the function t d (l), then the change of buoyancy of the electro-hydrostatic force adjusting actuator when driven can be written as:

[0038]

[0039] where l0is the corresponding absorbed distance after the voltage is applied, and Δv = v0- v air . When using the above equation to calculate the buoyancy change, the relationship between the absorbed distance l0and the applied voltage Φ needs to be determined first.

[0040] Further, when the shell interior space is connected with the atmosphere, the air pressure in the shell remains constant at p0, at which time the relationship between the voltage and the absorbed distance can be given by equation (6):

[0041]

[0042] When the designed function t d ​(l) the adsorption distance l0 can be obtained.

[0043] Further, when the inside of the shell is connected only to the closed air chamber and not connected to the atmospheric pressure, the volume change of the driver is related to the current air volume in the air chamber: t d (l0) the air volume of the current air chamber can be obtained by bringing formula (6):

[0044]

[0045] The adsorption distance l0 is calculated by simultaneously solving formula (7) and (9).

[0046] Compared with the prior art, the technical effect of the present application is that the present application provides an underwater buoyancy regulator based on a flexible electro-hydraulic driver, establishes a force-electric coupling model to analyze its deformation behavior under rigid constraint, reveals the relationship between the constraint gap, the driving pressure and the volume change, and explores the allowable space and optimization design method of the electric response flexible buoyancy regulator. The flexible electro-hydraulic driver provided by the present application has simple structure, utilizes the total volume change of the driver during driving, controls the adsorption process of the electro-hydraulic driver by changing the shell gap, and thus controls the buoyancy of the driver. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 is a structural schematic diagram of the electro-hydraulic buoyancy driver provided by the present application;

[0048] Figure 2 is a working principle schematic diagram of the electro-hydraulic buoyancy driver provided by the present application;

[0049] Figure 3 is a deformation analysis schematic diagram of the electro-hydraulic buoyancy driver provided by the present application;

[0050] In the figure: 1, voltage control module; 2, electro-hydraulic buoyancy adjustment driver; 2-1, shell; 2-2, electrode; 2-3, dielectric film capsule; 2-3-1, inner capsule; 2-3-2, outer capsule; 2-4, dielectric liquid; 2-5, sealing glue. DETAILED DESCRIPTION

[0051] The following examples can enable a person skilled in the art to have a more comprehensive understanding of the present application, but do not limit the present application in any way.

[0052] As Figure 1 shown, an electro-hydraulic buoyancy adjustment driver 2 provided by the present application is composed of a shell 2-1, an electrode 2-2, a dielectric film capsule 2-3, a dielectric liquid 2-4 and sealing glue 2-5, and is driven by a power control module 1.

[0053] The driving body of the electro-hydraulic buoyancy adjusting driver 2 is a dielectric film capsule 2-3 filled with dielectric liquid 2-4, which is composed of dielectric film and divided into two parts: a part covered by electrodes in the shell (inner capsule 2-3-1) and a part exposed to water and free to deform (outer capsule 2-3-2). The electrodes 2-2 covering the upper and lower surfaces of the dielectric film capsule 2-3 are connected to the positive and negative poles of the power supply control module 1 respectively.

[0054] The working principle of the electro-hydraulic buoyancy adjusting driver 2 provided by the present application is as follows:

[0055] When the electro-hydraulic buoyancy adjusting driver 2 is placed in water in an undriven state (no voltage load), the volume of the outer capsule 2-3-2 decreases due to the hydrostatic pressure, and the inner capsule 2-3-1 expands until the air pressure inside the shell 2-1 is equal to the hydrostatic pressure outside the shell 2-1.

[0056] As shown in Figure 2 When the voltage is applied, the Maxwell stress causes the two layers of dielectric film of the inner capsule 2-3-1 to be attracted together. This process starts in the area where the two layers of dielectric film are closest and gradually expands to the area where the two layers of dielectric film are farther apart, like a zipper. During this process, the liquid in the attraction area is gradually squeezed into the outer capsule 2-3-2, and the volume of the inner capsule 2-3-1 decreases until the Maxwell stress, air pressure and hydrostatic pressure reach a force balance state.

[0057] Assuming that the dielectric liquid is incompressible, the volume changes of the inner capsule 2-3-1 and the outer capsule 2-3-2 are consistent, and the shell 2-1 is rigidly constrained, i.e. the space inside the shell is fixed. At this time, the volume of the outer capsule 2-3-2 determines the total volume of the electro-hydraulic buoyancy adjusting driver 2. When the voltage increases, the volume of the outer capsule 2-3-2 increases, the overall volume becomes larger, a positive buoyancy is generated, and the driver floats up. Conversely, if the voltage decreases, the volume of the outer capsule 2-3-2 decreases, the overall volume of the driver becomes smaller, a negative buoyancy is generated, and the driver sinks.

[0058] For the control equation of the electro-hydraulic buoyancy adjusting driver 2 described above, the following method is used to establish it:

[0059] The control equation of the electro-hydraulic buoyancy adjusting driver 2 under rigid constraint is established by the principle of minimum energy. First, three assumptions in this model need to be explained. First, it is assumed that the dielectric film capsule 2-3 and the dielectric liquid 2-4 are ideal, i.e. both are incompressible materials, and the dielectric constant does not change with the change of electric field. Second, the dielectric film is assumed to be inextensible. Third, the gravitational potential energy of the dielectric liquid 2-4 is ignored, and the change of electrostatic energy stored in the unabsorbed area is also ignored.

[0060] When the system is in equilibrium state, the change of total free energy can be written as follows:

[0061] δU w + δU a + δU p + δU e = 0 (1)

[0062] where δU w and δU a are the potential energy changes of water and air respectively, δU p is the electrical energy change of the constant voltage source, and δU e is the electrical energy change stored in the adsorption region as a capacitor. Since the deformation energy of the membrane is neglected, the above equation can be written as:

[0063]

[0064] where δv water is the volume change of the outer capsule, δv air is the volume change of the inner capsule, Φ is the output voltage of the constant voltage source, and δc is the capacitance change of the dielectric membrane in the adsorption region. Considering that the dielectric liquid is incompressible in our model, δv water is equal to δv air , which is denoted as δv in the following. Meanwhile, since a constant voltage source is used, the charge change is dependent on the capacitance change δQ = Φδc.

[0065] As shown in FIG. 2A, when the device is actuated, the deformation of the inner capsule 2-3-1 is divided into two regions: the adsorption region and the non-adsorption region, and the length of the adsorption region is l. The outer capsule 2-3-2 only considers the volume change and does not focus on its specific deformation. Due to the effect of hydrostatic pressure, the membrane in the non-adsorption region will adhere to the inner wall, and the part that does not adhere is assumed to maintain the same shape before and after actuation. The deformation shape of the membrane adhering to the inner wall is determined by the shape of the inner wall of the outer shell 2-1, which in the two-dimensional case is determined by the gap t d . At this time, the volume change δv and the capacitance change δc can be expressed as functions of the length change δl of the adsorption region: Figure 3

[0066]

[0067] δv = t d bδl (4)

[0068] where ε is the dielectric constant of the dielectric membrane, b and l are the width and length of the adsorption region respectively, t f is the thickness of the membrane, and t d is the gap of the outer shell. Here, since both equations (3) and (4) are related to δl, the total free energy change can be written as a single-variable function related to δl. It should be noted that p water = p oil only before the outer capsule 2-3-2 is fully inflated into a cylindrical shape.​

[0069] By substituting equation (3) (4) into equation (2), the governing equation becomes:

[0070]

[0071] Considering the ideal gas law p air = p0v0 / v air and p water = p0+ ρgh, where p0is the atmospheric pressure, v0and v air are the initial and current air volume in the shell, respectively, equation (5) becomes:

[0072]

[0073] The above equation shows that the equivalent pressure provided by the Maxwell stress is related to the film thickness t f and the gap t d between the shell 2-1. Specifically, when the applied voltage can make the dielectric film extrude and absorb the dielectric liquid 2-4 with a thickness of t d , the absorption area of the dielectric film will extend by δl until the pressure is rebalanced, at which time the total volume change of the electro-hydrostatic force adjustment driver 2 becomes t d bδl. If the shape of the inner wall is artificially designed to satisfy the function t d (l) between the gap of the shell 2-1 and l, the change in buoyancy of the electro-hydrostatic force adjustment driver during driving can be written as:

[0074]

[0075] where l0is the corresponding absorption distance after the voltage is applied, and Δv = v0-v air . When using the above equation to calculate the amount of change in buoyancy, the relationship between the absorption distance l0and the applied voltage Φ needs to be determined first.

[0076] Considering two cases, when the space inside the shell 2-1 is connected to the atmosphere, the air pressure inside the shell 2-1 remains constant at p0, at which time the relationship between the voltage and the absorption distance can be given by equation (6):

[0077]

[0078] When the designed function t d (l) is given, the absorption distance l0can be obtained.

[0079] When the inside of the shell 2-1 is only connected to a closed air chamber and not connected to the atmospheric pressure, the volume change of the electro-hydrostatic force adjustment driver 2 is related to the current air volume in the air chamber. By substituting t d (l0) into equation (6), the current air volume of the air chamber can be obtained:

[0080]

[0081] The adsorption distance l0can be obtained by solving equations (7) and (9) simultaneously.

[0082] The maximum adsorption distance is limited by the size of the dielectric film capsule 2-3 and the total amount of dielectric liquid 2-4. First, the size of the inner capsule 2-3-1 should follow the principle of large width-length ratio, that is, the length in the l direction is less than the length in the b direction to ensure that the bag is deformed into a cylinder rather than a sphere. Second, the total amount of dielectric liquid 2-4 filled into the dielectric film capsule 2-3 should not exceed the maximum volume of the outer capsule 2-3-2 (i.e. the volume when deformed into a cylinder), otherwise the pressure inside the dielectric film capsule 2-3 during driving may be higher than the external hydrostatic pressure, resulting in the failure of the sealing glue 2-5 package.

[0083] The deformation of the dielectric film capsule 2-3 is determined by the shell gap t d (l) and thus the buoyancy adjustment performance of the electro-hydraulic buoyancy adjustment driver 2 can be adjusted by designing the gap of the shell 2-1.

[0084] Finally, it should be noted that the above is only a specific example of the present application. Obviously, the present application is not limited to the above embodiments, but can have many variations. All variations that can be directly derived or inferred from the disclosure of the present application by those of ordinary skill in the art should be considered within the scope of the present application.

Claims

1. An electro-hydraulic buoyancy regulating actuator, characterized in that, The actuator includes a housing, electrodes, a dielectric film capsule, and a dielectric fluid, and is driven by a power control module. The dielectric film capsule is divided into two parts: an inner capsule sealed in a shell and an outer capsule that is exposed to water and can deform freely; the dielectric film capsule is filled with dielectric fluid. The upper and lower surfaces of the inner capsule are covered with electrodes, which are connected to the power control module. When the actuator is placed in water and is in an undriven state / without voltage loading, the volume of the outer bladder decreases due to hydrostatic pressure, and the inner bladder expands until the air pressure inside the shell equals the hydrostatic pressure outside the shell; when in a driven state / with voltage applied, the volume of the inner bladder decreases until a force balance is reached between Maxwell stress, air pressure, and hydrostatic pressure. The inner capsule in The length of the direction is less than The length of the direction, the The direction is the length of the adsorption region, the The direction is the width of the adsorption region; the total amount of dielectric liquid filled into the dielectric film capsule does not exceed the maximum volume of the outer capsule; The control equations for the electro-hydraulic buoyancy regulating actuator under rigid constraints are established using the principle of minimum energy. When the system is in equilibrium, the change in total free energy is expressed as: in, and These are the changes in potential energy of water and air, respectively. It is the change in electrical energy of a constant voltage power supply. It is the change in electrical energy stored in the adsorption region as a capacitor; Furthermore, the change in total free energy is expressed as: in, It is a change in the volume of the external capsule. It is a change in the volume of the internal capsule. It is the output voltage of the constant voltage source. It is the change in capacitance of the dielectric thin film in the adsorption region. It is the external hydrostatic pressure. It is the gas pressure inside the actuator; Considering that dielectric fluid is incompressible, equal , to be denoted as Meanwhile, since a constant voltage source is used, the change in charge depends on the change in capacitance. ; When a voltage is applied, the inner capsule deforms into two regions: an adsorbed region and a non-adsorbed region. The length of the adsorbed region is... Volume change and capacitance change Expressed as a change in the length of the adsorption region Functions: in, It is the dielectric constant of the dielectric thin film. and These are the width and length of the adsorption region, respectively. It refers to the film thickness. It is the shell clearance; by formula , Attached In this case, the governing equations become: Consider the ideal gas law as well as ,in It is atmospheric pressure. It is the external liquid pressure. Where h is the density of the external liquid and h is the depth of the external liquid. and These are the initial and current internal air volumes, respectively, and the substitution method. get: 。 2. The electro-hydraulic buoyancy regulating actuator according to claim 1, characterized in that, When the voltage increases, the volume of the outer bladder increases, the overall volume increases, generating positive buoyancy, and the actuator floats upward; conversely, when the voltage decreases, the volume of the outer bladder decreases, the overall volume of the actuator decreases, generating negative buoyancy, and the actuator sinks.

3. The electro-hydraulic buoyancy regulating actuator according to claim 1, characterized in that, housing gap and The relation satisfies the function The change in buoyancy during operation of the electro-hydraulic buoyancy regulating actuator can be written as: in, It is the adsorption distance corresponding to the applied voltage. When using the above formula to calculate the change in buoyancy, the adsorption distance must first be determined. With applied voltage The relationship.

4. The electro-hydraulic buoyancy regulating actuator according to claim 3, characterized in that, When the internal space of the outer shell is open to the atmosphere, the air pressure inside the outer shell remains constant. At this point, the relationship between voltage and adsorption distance can be expressed by equation [equation missing]. Given: When given the designed function At that time, adsorption distance You can get it immediately.

5. The electro-hydraulic buoyancy regulating actuator according to claim 3, characterized in that, When the interior of the casing is only connected to a sealed air chamber and not to atmospheric pressure, the volume change of the actuator is related to the current air volume inside the chamber: Attached The current air volume in the air chamber can be obtained: Through joint , Calculate adsorption distance .

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