CN113595442B - Bidirectional displacement accumulation piezoelectric stack actuator capable of bearing pulling pressure and method thereof - Google Patents

Abstract

The invention discloses a bidirectional displacement accumulation piezoelectric stack actuator capable of bearing pulling pressure and a method thereof. The piezoelectric actuator comprises a shell component, a motor component, two elastic connectors, two driving nuts, a first piezoelectric stack component, a second piezoelectric stack component and a screw rod component; the first piezoelectric stack component and the second piezoelectric stack component deform through the inverse piezoelectric effect respectively, the screw rod component and the driving nut are pushed to move up and down, the motor component operates, the driving nut is driven to rotate along the screw rod, the position of the driving nut is recovered, the process is repeated continuously, and accordingly motion accumulation of the screw rod component is achieved. The invention can utilize the inverse piezoelectric effect to ensure that the driver can realize continuous bidirectional displacement accumulation through the extension and retraction of the piezoelectric stack when bearing the tensile pressure, thereby realizing the rapid large-amplitude extension and retraction of the output rod.

Description

Bidirectional displacement accumulation piezoelectric stack actuator capable of bearing pulling pressure and method thereof

Technical Field

The invention relates to the technical field of piezoelectric drivers. In particular to a bidirectional displacement accumulation piezoelectric stack actuator capable of bearing pulling pressure and a method thereof.

Background

The piezoelectric actuator is a type of element which utilizes the inverse piezoelectric effect to control the mechanical deformation of a piezoelectric body through an electric field so as to generate linear motion, and is widely applied to the fields of aeronautics, measurement technologies, precision machining, medical instruments and the like. However, the conventional piezoelectric actuator operates under a pressurized condition, and thus, the conventional piezoelectric actuator can only operate under a unidirectional load, so that the conventional piezoelectric actuator is difficult to operate under various loads in an external environment, and the use condition is limited.

Disclosure of Invention

In order to solve the limitation that the existing piezoelectric actuator can only drive under a compression load, the invention aims to provide a piezoelectric actuator device which can drive the piezoelectric actuator under the compression load and a tension load.

In order to achieve the purpose, the piezoelectric stacks are arranged at the two ends of the piezoelectric driver, and the piezoelectric stacks are converted into displacement accumulation of the screw rod moving up and down by the extension and retraction of the piezoelectric stacks by depending on the inverse piezoelectric effect of the lower piezoelectric stacks, so that the operation of the piezoelectric driver under a pressed load is realized; by means of the inverse piezoelectric effect of the upper piezoelectric stack, the expansion and contraction of the piezoelectric stack is converted into the displacement accumulation of the up-and-down movement of the screw, so that the piezoelectric driver can operate under the tension load.

The invention specifically adopts the following technical scheme:

in one aspect, the invention provides a bi-directional displacement accumulation piezoelectric stack actuator capable of bearing tension and pressure, which comprises a housing assembly, a motor assembly, two elastic connectors, a first driving nut, a second driving nut, a first piezoelectric stack assembly, a second piezoelectric stack assembly and a screw rod assembly, wherein the motor assembly, the two elastic connectors, the first driving nut, the second driving nut, the first piezoelectric stack assembly, the second piezoelectric stack assembly and the screw rod assembly are coaxially arranged in an inner cavity of the housing assembly;

the motor assembly is fixed in the middle of an inner cavity of the shell assembly, the first driving nut and the second driving nut are respectively arranged on two sides of the motor assembly, and the first driving nut and the second driving nut are respectively connected with the motor assembly through an elastic connector;

the motor assembly can bidirectionally drive the first drive nut and the second drive nut to rotate around the axis through the elastic connectors, each elastic connector has a telescopic freedom degree along the axial direction, and when the drive nut connected with each elastic connector is limited to rotate around the axis and the motor assembly continues to drive, the elastic connectors also have elastic deformation allowance so that the elastic connectors can be reversibly twisted circumferentially;

one end of the first piezoelectric stack component is fixed on the end wall of one side of the inner cavity of the shell component, and the end face of the other end of the first piezoelectric stack component is used as a compression surface matched with the first driving nut; one end of the second piezoelectric stack component is fixed on the other end wall of the inner cavity of the shell component, and the end face of the other end of the second piezoelectric stack component is used as a compression surface matched with the second driving nut;

the screw component is arranged in a central channel which sequentially penetrates through the second piezoelectric stack component, the second driving nut, the first elastic connector, the through motor component, the second elastic connector, the first driving nut and the first piezoelectric stack component, one end of the screw component is used as a displacement output end and extends out of the top of the shell component, the other end of the screw component is limited by a group of limiting components in an inner cavity of the second piezoelectric stack component in an axial movement range, and the screw component does not have the degree of freedom of circumferential rotation around an axis; the middle part of the screw rod component is provided with an external thread section, and the first driving nut and the second driving nut are respectively matched with the external thread section to form a thread pair;

when the displacement output end is under the action of pressure, the first piezoelectric stack component pushes the screw rod component to move axially through inverse piezoelectric effect deformation, the motor component drives the first driving nut and the second driving nut to operate, the positions of the first driving nut and the second driving nut are recovered, and the process is repeated continuously so as to realize displacement accumulation of the screw rod component; when the displacement output end is under the action of a tensile force, the second piezoelectric stack component pushes the screw rod component to move axially through inverse piezoelectric effect deformation, the motor component drives the first driving nut and the second driving nut to operate, the positions of the first driving nut and the second driving nut are recovered, and accordingly displacement accumulation of the screw rod component is achieved repeatedly.

Preferably, the shell assembly comprises a first piezoelectric stack shell, a motor shell, a second piezoelectric stack shell, a first nut support plate and a second nut support plate, one end of the motor shell is connected with one end of the first piezoelectric stack shell through the first nut support plate, and the other end of the motor shell is connected with one end of the second piezoelectric stack shell through the second nut support plate;

the motor assembly is fixedly arranged in the motor shell, the first piezoelectric stack assembly and the first driving nut are arranged in the first piezoelectric stack shell, the second piezoelectric stack assembly and the second driving nut are arranged in the second piezoelectric stack shell, the other end of the first piezoelectric stack shell is sealed by a lower bottom cover, and the other end of the second piezoelectric stack shell is sealed by an upper bottom cover.

Preferably, the lower bottom cover and the upper bottom cover both comprise a disc for end sealing, and a hollow shaft section and a ball spline which are positioned in the inner cavity of the shell component, one end of the hollow shaft section is vertically installed on the disc, the other end of the hollow shaft section is installed with the ball spline, and polish rod sections on two sides of the screw rod component except for the middle external thread section respectively penetrate through the ball spline on the side, so that the screw rod component is limited to move only along the axial direction and cannot rotate and move radially.

Preferably, the limiting assemblies are two limiting blocks, two spaced limiting holes are formed in the hollow shaft section on the lower bottom cover, and a limiting block for limiting the axial movement range of the screw assembly is arranged in each limiting hole in an interference manner.

Preferably, the motor assembly comprises a frameless torque motor fixedly connected in a motor shell, and a first motor connecting shaft and a second motor connecting shaft which are respectively and fixedly connected to two sides of a rotor in the frameless torque motor, output ends of the first motor connecting shaft and the second motor connecting shaft are respectively in interference fit with a bearing, and the two bearings are both fixedly installed in the shell assembly and provide rotating support for the first motor connecting shaft and the second motor connecting shaft.

Preferably, each elastic connector comprises a hollow first connector and a hollow second connector, a plurality of rubber sheets are arranged at one end of each first connector, blocking strips with the same number as the rubber sheets on the first connector are arranged on the inner wall of each second connector, and the blocking strips are arranged along the axial direction; under the matching state of the first connector and the second connector, a rubber sheet attached to the inner wall of the second connector is just inserted between every two barrier strips, no gap exists between the barrier strips and the rubber sheet, and the first connector can move in the second connector along the axial direction and can be twisted by a certain angle through the deformation of the rubber sheet through the matching of the barrier strips and the rubber sheet; in the elastic connector on each side of the motor assembly, the first connector is fixedly connected with the motor connecting shaft on the side for transmission, and the second connector is fixedly connected with the driving nut on the side for transmission.

Preferably, the first piezoelectric stack assembly comprises a first piezoelectric stack and a first piezoelectric stack cover which are fixedly clamped, the second piezoelectric stack assembly comprises a second piezoelectric stack and a second piezoelectric stack cover which are fixedly clamped, and gaps necessary for circumferential deformation are reserved on the inner and outer walls of the first piezoelectric stack and the second piezoelectric stack; the second drive nut is only capable of axial movement between the second nut support plate and the second piezoelectric stack cover; the first drive nut is only axially movable between the first nut support plate and the first piezoelectric stack cover.

Preferably, the screw assembly comprises a screw, a first supporting shaft and a second supporting shaft which are fixedly connected to two ends of the screw respectively, the first supporting shaft and the second supporting shaft are both optical axes, and the tail end of the first supporting shaft is connected with a limiting check ring; the screw rod passes through external screw thread and first drive nut and second drive nut threaded connection, and spacing retaining ring is located two between the stopper, the terminal end fixedly connected with of second back shaft stretches out the external nut of shell subassembly.

Preferably, the second support shaft is provided with a second shaft groove matched with the ball spline on the side, and the first support shaft is provided with a first shaft groove matched with the ball spline on the side.

In another aspect, the present invention provides an actuating method of a bidirectional displacement accumulation piezoelectric stack actuator according to any of the above aspects, which includes: receive external load with displacement output end direction up with two-way displacement accumulation piezo-electric stack actuator to according to load type and appointed displacement output direction through control motor element's drive direction carries out the displacement accumulation:

the first driving state: when the screw assembly is subjected to pressure load, the first driving nut and the second driving nut are driven to move until the lower end face of the second driving nut abuts against the second nut supporting plate, and the lower end face of the first driving nut abuts against the first piezoelectric stack cover; the first piezoelectric stack works, the two driving nuts and the screw rod assembly are pushed to synchronously move upwards by stretching through the inverse piezoelectric effect, at the moment, the frameless torque motor is controlled to drive the second driving nut to rotate in the positive direction so as to move downwards until the lower end face of the second driving nut abuts against the second nut supporting plate, and the lower end face of the first driving nut abuts against the first piezoelectric stack cover so as not to rotate, so that the energy of the frameless torque motor driving the first driving nut is stored in the lower elastic connector; when the length of the first piezoelectric stack is recovered, the lower end face of the second driving nut abuts against the second nut supporting plate and cannot rotate, and a gap exists between the first driving nut and the first piezoelectric stack cover, so that energy in the elastic connector at the lower part is released to drive the first driving nut to rotate forward and move downward until the lower end face of the first driving nut abuts against the first piezoelectric stack cover; during the continuous compression of the screw assembly, the upward displacement of the screw assembly is accumulated by continuously repeating the process, so that the screw moves upward to output the displacement;

the second driving state: when the screw assembly is subjected to pressure load, the first driving nut and the second driving nut are driven to move until the lower end face of the second driving nut abuts against the second nut supporting plate, and the lower end face of the first driving nut abuts against the first piezoelectric stack cover; the first piezoelectric stack works, the two driving nuts and the screw rod assembly are pushed to synchronously move upwards by stretching through the inverse piezoelectric effect, the frameless torque motor is controlled to drive the second driving nut to reversely rotate for a certain angle so as to move upwards, the lower end face of the first driving nut abuts against the first piezoelectric stack cover and cannot rotate, and therefore energy of the frameless torque motor driving the first driving nut is stored in the lower elastic connector; when the length of the first piezoelectric stack is shortened until the lower end face of the second driving nut abuts against the second nut supporting plate, the screw assembly has a relatively downward displacement relative to the initial state, and at the moment, a gap exists between the first driving nut and the first piezoelectric stack cover, so that the energy in the elastic connector at the lower part is released, the first driving nut is driven to reversely rotate so as to move upwards, until the first driving nut is restored to the initial position, namely the energy in the elastic connector at the lower part is completely released; then the length of the first piezoelectric stack is recovered to the initial state; by continuously repeating this process while the screw assembly is continuously pressurized, the downward displacement of the screw assembly is accumulated, thereby moving the screw downward to output the displacement;

the third driving state: when the screw rod assembly is under tension load, the first driving nut and the second driving nut are driven to move until the upper end face of the first driving nut abuts against the first nut supporting plate, and the upper end face of the second driving nut abuts against the second piezoelectric stack cover; the second piezoelectric stack works, the two driving nuts and the screw rod assembly are pushed to synchronously move downwards by stretching through the inverse piezoelectric effect, the frameless torque motor is controlled to drive the first driving nut to rotate forward by a certain angle so as to move downwards, the upper end face of the second driving nut abuts against the second piezoelectric stack cover and cannot rotate, and therefore energy of the frameless torque motor driving the second driving nut is stored in the upper elastic connector; when the length of the second piezoelectric stack is shortened until the upper end face of the first driving nut abuts against the first nut supporting plate, the screw assembly has a relatively upward displacement relative to the initial state, and at the moment, a gap exists between the second driving nut and the second piezoelectric stack cover, so that the energy in the elastic connector at the upper part is released, the second driving nut is driven to rotate forward to move downwards until the second driving nut returns to the initial position, namely the energy in the elastic connector at the upper part is completely released; then the length of the second piezoelectric stack is recovered to the initial state; during the continuous tension of the screw assembly, accumulating the upward displacement of the screw assembly by continuously repeating the process, thereby moving the screw downward to output the displacement;

the fourth driving state: when the screw assembly is under tension load, the upper end face of the first driving nut abuts against the first female support plate, and the first driving nut and the second driving nut are driven to move until the upper end face of the second driving nut abuts against the second piezoelectric stack cover; the second piezoelectric stack works, the two driving nuts and the screw component are pushed to synchronously move downwards by the extension of the inverse piezoelectric effect, and at the moment, the frameless torque motor is controlled to drive the first driving nut to reversely rotate so as to move upwards until the upper end face of the first driving nut abuts against the first nut supporting plate and the upper end face of the second driving nut abuts against the second piezoelectric stack cover so as to be incapable of rotating, so that the energy of the frameless torque motor driving the second driving nut is stored in the upper elastic connector; when the length of the second piezoelectric stack is recovered, the upper end face of the first driving nut abuts against the first nut supporting plate and cannot rotate, and a gap exists between the second driving nut and the second piezoelectric stack cover, so that energy in the elastic connector at the upper part is released to drive the second driving nut to rotate reversely so as to move upwards until the upper end face of the second driving nut abuts against the second piezoelectric stack cover; by repeating this process continuously while the screw assembly is continuously pulled, the downward displacement of the screw assembly is accumulated, thereby moving the screw downward to output a displacement.

Compared with the prior art, the invention has the following advantages:

according to the invention, the upper end and the lower end of the piezoelectric driver are respectively provided with the piezoelectric stacks, the operation of the device under a compression load can be realized through the operation of the first piezoelectric stack, and the operation of the device under a tension load can be realized through the operation of the second piezoelectric stack; the designed structure is compact, the processing is simple, the assembly is simple and convenient, the parts inside can be replaced easily, the application range is wide, the application value is high in the fields of precision driving, precision instruments, aerospace and aviation and the like, and the practicability is high.

Drawings

FIG. 1 is a general schematic diagram of a bi-directional displacement accumulation piezoelectric stack actuator capable of withstanding tensile and compressive forces and method of the present invention;

FIG. 2 is a cross-sectional view of a bi-directional displacement-accumulating piezoelectric stack actuator capable of withstanding a pulling pressure and method thereof;

FIG. 3 is an exploded view of the housing assembly;

FIG. 4 is an exploded view of the motor assembly;

FIG. 5 is an exploded view of the elastomeric connector;

FIG. 6 is an exploded view of a first piezo stack assembly;

FIG. 7 is an exploded view of a second piezo stack assembly;

FIG. 8 is an exploded view of the screw assembly;

FIG. 9 is a schematic diagram of an embodiment of a bi-directional displacement accumulation piezo-electric stack actuator capable of withstanding a pulling pressure and a method thereof;

in the figure, the position of the upper end of the main shaft, the piezoelectric actuator comprises a housing assembly 1, a lower base cover 11, a first disc 111, a hollow shaft section 112, a limiting hole 113, a first ball spline 12a, a second ball spline 12b, a first piezoelectric stack housing 13, a first nut support plate 14a, a second nut support plate 14b, a first boss 141a, a second boss 141b, a motor housing 15, an upper base cover 16, a second disc 161, a second piezoelectric stack housing 17, a limiting block 18, a motor assembly 2, a frameless torque motor 21, a first washer 22, a second washer 23, a first motor connecting shaft 24, a second motor connecting shaft 25, a bearing 26, an elastic connector 3, a first connector 31, a rubber sheet 32, a second connector 33, a barrier strip 34, a first driving nut 4a, a second driving nut 4b, a first piezoelectric stack assembly 5, a first piezoelectric stack 51, a first piezoelectric stack cover 52, a first piezoelectric stack protrusion 53, a first piezoelectric stack connecting hole 54, a second piezoelectric stack assembly 6, a second piezoelectric stack assembly 61, a second piezoelectric stack assembly 62, a second piezoelectric stack protrusion 731, a second screw rod support hole 71, a second screw rod support groove 73, a second support shaft support hole 721, a second screw rod support groove 73, a support groove 73 and a support.

Detailed Description

The invention relates to a bidirectional displacement accumulation piezoelectric stack actuator capable of bearing tension and pressure and a method thereof.

The invention is further described below with reference to the accompanying drawings:

as shown in fig. 1 and 2, in a preferred embodiment of the present invention, a bi-directional displacement-accumulating piezo stack actuator capable of withstanding a pulling pressure is provided, and its basic structure includes a housing assembly 1, and a motor assembly 2, two elastic connectors 3, a first drive nut 4a, a second drive nut 4b, a first piezo stack assembly 5, a second piezo stack assembly 6, and a screw assembly 7 coaxially disposed in an inner cavity of the housing assembly 1, wherein central axes of the motor assembly 2, the two elastic connectors 3, the first drive nut 4a, the second drive nut 4b, the first piezo stack assembly 5, the second piezo stack assembly 6, and the screw assembly 7 coincide with a central axis of the housing assembly 1. Referring to fig. 2, the motor assembly 2 is fixed in the middle of the inner cavity of the housing assembly 1, the first driving nut 4a and the second driving nut 4b are respectively disposed on two sides of the motor assembly 2, and the first driving nut 4a and the second driving nut 4b are respectively connected to the motor assembly 2 through an elastic connector 3. The position of the motor assembly 2 in the housing assembly 1 is relatively fixed, and when the housing assembly 1 is in operation, the first drive nut 4a and the second drive nut 4b can be driven to rotate around the axis in a bidirectional manner through the elastic connector 3, wherein the bidirectional drive means that the motor assembly can drive forward rotation and reverse rotation, and the specific drive direction of the motor assembly can be set through an external motor controller. The elastic connector 3 is a connector which has certain elasticity and can be reversibly deformed under the action of external force, and the elasticity is mainly reflected in the twisting direction. Specifically, each of the resilient connectors 3 has its own degree of freedom of expansion and contraction in the axial direction, so that the first and second drive nuts 4a, 4b can move axially relative to the motor assembly 2 to a certain extent, but remain in connected engagement with the motor assembly 2 at all times. When the drive nut (the first drive nut 4a or the second drive nut 4 b) to which each elastic connector 3 is connected is not restricted from rotating about the axis, the motor assembly 2 can freely drive the connected drive nut to rotate, but when the drive nut (the first drive nut 4a or the second drive nut 4 b) to which each elastic connector 3 is connected is restricted from rotating about the axis while the motor assembly 2 continues to drive, the elastic connector 3 needs to have a corresponding elastic deformation capability, i.e., it should have an elastic deformation margin in the twisting direction so that it can be reversibly twisted circumferentially. It is noted that this twisting needs to be reversible, i.e. the energy accumulated by the deformation should be released when the external force is removed, so that the elastic connector 3 is restored to its original shape.

In addition, in this embodiment, two piezoelectric stack assemblies are respectively disposed at the upper end and the lower end of the piezoelectric actuator, so as to be capable of receiving both a compressive load and a tensile load, and one end of each of the two piezoelectric stack assemblies needs to be kept fixed. Wherein, the one end of first piezo-stack subassembly 5 is fixed in on the one side end wall of shell subassembly 1 inner chamber, and the other end terminal surface is as receiving the surface with first drive nut 4a complex, and first drive nut 4a can support and exert the effort to first piezo-stack subassembly 5 on receiving the surface to cause the inverse piezoelectric effect to warp. Similarly, one end of the second piezo-stack assembly 6 is fixed on the other end wall of the inner cavity of the housing assembly 1, the other end face is used as a pressed face matched with the second driving nut 4b, and the second driving nut 4b can abut against the pressed face to exert an acting force on the second piezo-stack assembly 6, so that the inverse piezo-electric effect is caused to deform.

External load in the bidirectional displacement accumulation piezoelectric stack actuator is transmitted through the screw component 7, and displacement is output outwards through the screw component 7, so that the actuating function is realized. The second piezo-stack assembly 6, the second driving nut 4b, the first elastic connector 3, the through motor assembly 2, the second elastic connector 3, the first driving nut 4a and the first piezo-stack assembly 5 are all designed to be hollow inside and are connected in sequence to form a through central passage. The screw assembly 7 is placed in the central channel in the inner cavity of the shell assembly 1, one end of the screw assembly is used as a displacement output end and extends out of the top of the shell assembly 1, the other end of the screw assembly is limited in the axial movement range by a group of limiting assemblies in the inner cavity of the second piezoelectric stack assembly 6, and the screw assembly 7 does not have the freedom of circumferential rotation around the axis. The middle part of the screw rod component 7 is an external thread section, and the first driving nut 4a and the second driving nut 4b are respectively matched with the external thread section to form a thread pair. Since the screw assembly 7 is restricted by other members and therefore does not have a degree of freedom of circumferential rotation about the axis, it is possible to smoothly slide up and down the thread on the male thread section of the screw assembly 7 when the first drive nut 4a and the second drive nut 4b are driven by the motor assembly 2.

For the bidirectional displacement accumulation piezoelectric stack actuator, the bidirectional displacement accumulation piezoelectric stack actuator can be subjected to pressure to realize bidirectional actuation and can also be subjected to tension to realize bidirectional actuation. When the pressure is applied to the displacement output end of the screw component 7, the first piezoelectric stack component 5 pushes the screw component 7 to move axially through inverse piezoelectric effect deformation, and then the motor component 2 drives the first driving nut 4a and the second driving nut 4b to operate, so that the positions of the first driving nut 4a and the second driving nut 4b are restored and repeated continuously, and the displacement accumulation of the screw component 7 is realized; when the displacement output end of the screw component 7 is under the action of tensile force, the second piezoelectric stack component 6 pushes the screw component 7 to move axially through inverse piezoelectric effect deformation, and then the motor component 2 drives the first driving nut 4a and the second driving nut 4b to operate, so that the positions of the first driving nut 4a and the second driving nut 4b are recovered, and the displacement accumulation of the screw component 7 is realized repeatedly. The displacement accumulation means that the displacements of the screw assembly 7 in different operation cycles are accumulated continuously, so that an increasing displacement stroke is output outwards.

The basic operating principle of the bi-directional displacement accumulation piezoelectric stack actuator capable of withstanding tensile and compressive forces according to the present invention is described above, and the following detailed description is provided for the implementation of each basic structure of the actuator in a preferred embodiment of the present invention. For convenience of description, the present invention will be described hereinafter with reference to the displacement output end of the screw assembly 7 as the upper end on one side and the lower end on the other side. However, in practical applications, the overall posture of the device may be turned over to some extent, and the device does not necessarily need to be operated in a vertical state.

In the present embodiment, in order to ensure that one end of the piezoelectric stack is in a fixed state during operation, referring to fig. 2 and 3, the housing assembly 1 includes a first piezoelectric stack housing 13, a motor housing 15, a second piezoelectric stack housing 17, a first nut support plate 14a and a second nut support plate 14b, one end of the motor housing 15 is connected to one end of the first piezoelectric stack housing 13 through the first nut support plate 14a, and the other end of the motor housing 15 is connected to one end of the second piezoelectric stack housing 17 through the second nut support plate 14 b. The motor component 2 is fixedly arranged in a motor shell 15 and is limited to move up and down, the first piezoelectric stack component 5 and the first driving nut 4a are arranged in a first piezoelectric stack shell 13, the second piezoelectric stack component 6 and the second driving nut 4b are arranged in a second piezoelectric stack shell 17, the other end of the first piezoelectric stack shell 13 is sealed by a lower bottom cover 11, and the other end of the second piezoelectric stack shell 17 is sealed by an upper bottom cover 16. The lower bottom cover 11 and the upper bottom cover 16 both comprise a disk for end sealing, and a hollow shaft section and a ball spline which are positioned in the inner cavity of the shell component 1, one end of the hollow shaft section is vertically installed on the disk, the other end of the hollow shaft section is installed with the ball spline, and two side polished rod sections of the screw rod component 7 except for the middle external thread section respectively pass through the ball spline on the side, so that the screw rod component 7 is limited to move only along the axial direction and cannot rotate and move in the radial direction. The limiting components are two limiting blocks 18, two spaced limiting holes 113 are formed in the hollow shaft section on the lower bottom cover 11, and a limiting block 18 for limiting the axial movement range of the screw component 7 is arranged in each limiting hole 113 in an interference mode.

Specifically, referring to fig. 3, the positional relationship of the subcomponents in the case assembly 1 is as follows: the lower bottom cover 11 is composed of a first disc 111, a first hollow shaft section 112 and a first ball spline 12a, the upper end of the first disc 111 is provided with the hollow shaft section 112, and the hollow shaft section 112 is arranged below the first ball spline 12 a; the upper and lower covers 16 are composed of a second disc 161, a second hollow shaft section 112 and a second ball spline 12b, the second disc 161 and the lower end are provided with the second hollow shaft section 112, and the second hollow shaft section 112 is positioned above the second ball spline 12 b. The rod section of the screw assembly 7 near the displacement output end passes through the second hollow shaft section 112, while the rod section far from the displacement output end passes through the first hollow shaft section 112. The upper end of the first disc 111 is fixedly connected with a first piezoelectric stack shell 13, the upper end of the first piezoelectric stack shell 13 is fixedly connected with a first nut support plate 14a, the upper end of the first nut support plate 14a is in threaded connection with a motor shell 15, the upper end of the motor shell 15 is in threaded connection with a second nut support plate 14b, the upper end of the second nut support plate 14b is fixedly connected with a second piezoelectric stack shell 17, and the upper end of the second piezoelectric stack shell 17 is fixedly connected with the lower end of a second disc 161 on the upper portion of an upper bottom cover 16.

In this embodiment, in order to fix the motor in the motor housing 15 and achieve a corresponding driving effect, referring to fig. 2 to 4, the motor assembly 2 includes a frameless torque motor 21 fixedly connected in the motor housing 15, and a first motor connecting shaft 24 and a second motor connecting shaft 25 fixedly connected to two sides of an inner rotor of the frameless torque motor 21, respectively, where the second motor connecting shaft 25 is fixedly connected to an upper portion of the inner rotor of the frameless torque motor 21, the first motor connecting shaft 24 is fixedly connected to a lower portion of the inner rotor of the frameless torque motor 21, an output end of an upper portion of the first motor connecting shaft 24 and an output end of a lower portion of the second motor connecting shaft 25 are respectively in interference fit with a bearing 26, and both the bearings 26 are fixedly installed in the housing assembly 1 to provide a rotational support for the first motor connecting shaft 24 and the second motor connecting shaft 25. Meanwhile, in order to ensure the reliability of the bearing operation and installation in the present embodiment, a first washer 22 is installed between the bearing 26 near the upper portion and the upper end of the frameless torque motor 21, and a second washer 23 is installed between the bearing 26 near the lower portion and the lower end of the frameless torque motor 21. In order to restrict the movement of the two bearings 26, a second boss 141b may be provided on the upper portion of the inner hole of the second nut support plate 14b, the lower end surface of the second boss 141b may abut against the upper end surface of the outer ring of the bearing 26 near the upper portion, a first boss 141a may be provided on the lower portion of the inner hole of the first nut support plate 14a, and the upper end surface of the first boss 141a may abut against the lower end surface of the outer ring of the bearing 26 near the lower portion.

In the present embodiment, in order to enable the frameless torque motor 21 to drive the upper and lower drive nuts 4 asynchronously, as seen in fig. 2-5, each of the elastic connectors 3 comprises a hollow first connector 31 and a hollow second connector 33, both of which are in the form of circular rings. One end of the first connector 31 is fixedly provided with a plurality of rubber sheets 32, and the plurality of rubber sheets 32 are integrally arranged around the circumferential direction of the first connector 31 to form a cylindrical form. The inner wall of the second connector 33 is provided with the same number of barrier strips 34 as the rubber sheets 32 on the first connector 31, and the barrier strips 34 are arranged along the axial direction. In this embodiment, the number of the rubber sheet 32 and the barrier strip 34 is 5. In the state that the first connector 31 and the second connector 33 are fitted, a rubber sheet 32 which is attached to the inner wall of the second connector 33 is just inserted between every two barrier strips 34, and there is no gap between the barrier strips 34 and the rubber sheet 32, so that the first connector 31 can move in the second connector 33 along the axial direction and can be twisted by the deformation of the rubber sheet 32 by the fitting of the barrier strips 34 and the rubber sheet 32, but the rubber sheet 32 has a maximum twisting angle because the twisting is not infinite. The rubber sheet 32 can be accumulated during the twisting process, and then when the torque disappears and the external force is not applied, the accumulated energy in the rubber sheet can be released, and the connected driving nut is driven to rotate. In the elastic connector 3 at each side of the motor component 2, the first connector 31 is fixedly connected and driven with the motor connecting shaft at the side, and the second connector 33 is fixedly connected and driven with the driving nut at the side. Specifically, referring to fig. 2, the outer wall of the first connector 31 at the upper end of the motor assembly 2 is fixedly connected with the inner hole of the second connecting shaft 24, the second connector 33 is located at the side of the first connector 31 far away from the motor assembly 2, and the second connector 33 is fixedly connected with the second driving nut 4b at the upper end of the motor assembly 2; the outer wall of the first connector 31 at the lower end of the motor assembly 2 is fixedly connected with the inner wall of the first connecting shaft 25, and the second connector 33 is fixedly connected with the first driving nut 4a at the lower end of the motor assembly 2, so that when the first driving nut 4a or the second driving nut 4b of the driving nut is subjected to axial pressure, the energy of the frameless torque motor 21 driving the driving nut 4 can be stored in the elastic connector 3, and when the axial force applied to the driving nut disappears, the elastic connector 3 releases the stored energy to drive the driving nut 2 to rotate.

In the present embodiment, in order to allow a certain axial movement space for the two driving nuts, referring to fig. 2, 6 and 7, the first piezo stack assembly 5 includes a first piezo stack 51 and a first piezo stack cover 52 that are fixed in a snap-fit manner, and the second piezo stack assembly 6 includes a second piezo stack 61 and a second piezo stack cover 62 that are fixed in a snap-fit manner. In addition, when the piezoelectric stacks are deformed in an axial direction, the piezoelectric stacks are deformed to a certain extent in the circumferential direction, so that gaps necessary for circumferential deformation need to be left on the inner and outer walls of the first piezoelectric stack 51 and the second piezoelectric stack 61. The clamping between the piezoelectric stack and the piezoelectric stack cover can be realized by arranging corresponding bulges and connecting holes, in the embodiment, the upper end of the second piezoelectric stack 61 is provided with a second piezoelectric stack bulge 63, and the lower part of the second piezoelectric stack cover 62 is provided with a second piezoelectric stack connecting hole 64 which is in interference connection with the second piezoelectric stack bulge 63; the lower end of the first piezoelectric stack 51 is provided with a first piezoelectric stack bulge 53, and the lower part of the first piezoelectric stack cover 52 is provided with a first piezoelectric stack connecting hole 54 which is in interference connection with the first piezoelectric stack bulge 53. The axial travel of the two drive nuts is also limited, the second drive nut 4b being axially movable only between the second nut support plate 14b and the second piezoelectric stack cover 62, while the first drive nut 4a being axially movable only between the first nut support plate 14a and the first piezoelectric stack cover 52.

In this embodiment, in order to ensure that the screw 71 does not damage the device due to exceeding the stroke during the movement process, a limiting retaining ring 74 is additionally provided, referring to fig. 2, 3, and 8, the screw assembly 7 includes the screw 71, and a first supporting shaft 72 and a second supporting shaft 73 respectively fixedly connected to two ends of the screw 71, the first supporting shaft 72 and the second supporting shaft 73 are both optical axes, and the end of the first supporting shaft 72 is connected to the limiting retaining ring 74. The second support shaft 73 is fixedly connected to the upper end of the screw rod 71, the first support shaft 72 is fixedly connected to the lower end of the screw rod 71, and the limit retainer ring 74 is fixedly connected to the lower end of the first support shaft 72. The screw 71 is screwed to the first drive nut 4a and the second drive nut 4b via external threads, and the limit stopper 74 is located between the two limit stoppers 18 so that the two limit stoppers 18 define a slidable range of the limit stopper 74. An external nut 8 extending out of the housing assembly 1 is fixedly connected to an upper end portion of the second support shaft 73. The external nut 8 may be connected to an external belt-driven device.

In this embodiment, in order to ensure that the screw 71 only moves linearly and does not rotate when moving, as shown in fig. 7, a second shaft groove 731 for engaging with the ball spline on the side may be provided on the second support shaft 73, and a first shaft groove 721 for engaging with the ball spline on the side may be provided on the first support shaft 72.

Based on the bidirectional displacement accumulation piezoelectric stack actuator, the invention also provides an actuating method using the bidirectional displacement accumulation piezoelectric stack actuator, which receives an external load in a direction that a displacement output end faces upwards, and carries out displacement accumulation by controlling the driving direction of the motor component 2 according to the load type and the appointed displacement output direction, and the schematic diagram of the actuator is shown in fig. 9, and the specific implementation process is as follows:

a first driving state: when the screw assembly 7 is subjected to a compressive load, the first driving nut 4a and the second driving nut 4b are driven to move until the lower end face of the second driving nut 4b abuts against the second nut supporting plate 14b, and the lower end face of the first driving nut 4a abuts against the first piezoelectric stack cover 52; the first piezoelectric stack 51 works, the two driving nuts and the screw assembly 7 are pushed to synchronously move upwards by stretching through the inverse piezoelectric effect, at this time, the frameless torque motor 21 is controlled to rotate forwards, and the screw assembly 7 can only move axially and cannot rotate, so that the second driving nut 4b is driven to rotate forwards and move downwards until the lower end face of the second driving nut 4b abuts against the second nut supporting plate 14b, and the lower end face of the first driving nut 4a abuts against the first piezoelectric stack cover 52 and cannot rotate, so that the energy of the frameless torque motor 21 driving the first driving nut 4a is stored in the lower elastic connector 3; when the length of the first piezoelectric stack 51 is recovered, the lower end surface of the second driving nut 4b abuts against the second nut support plate 14b, so that the second driving nut 4b cannot rotate with the screw assembly 7, and a gap exists between the first driving nut 4a and the first piezoelectric stack cover 52, so that energy in the elastic connector 3 at the lower part is released, the first driving nut 4a is driven to rotate forward, and the first driving nut 4a moves downward until the lower end surface of the first driving nut 4a abuts against the first piezoelectric stack cover 52. The above-mentioned process is an actuation cycle, and during the time that the screw assembly 7 is continuously pressed, the upward displacement of the screw assembly 7 is accumulated by continuously repeating the cycle process, so that the screw 71 is moved upward to output the displacement.

A second driving state: when the screw assembly 7 is subjected to a compressive load, the first driving nut 4a and the second driving nut 4b are driven to move until the lower end face of the second driving nut 4b abuts against the second nut supporting plate 14b, and the lower end face of the first driving nut 4a abuts against the first piezoelectric stack cover 52; the first piezoelectric stack 51 works, the two driving nuts and the screw assembly 7 are pushed to synchronously move upwards by stretching through the inverse piezoelectric effect, at this time, the frameless torque motor 21 is controlled to drive the second driving nut 4b to reversely rotate for a certain angle, and the screw assembly 7 can only axially move but cannot rotate, so that the second driving nut 4b reversely rotates for a certain angle to move upwards, and the lower end face of the first driving nut 4a abuts against the first piezoelectric stack cover 52 and cannot rotate, so that the energy of the frameless torque motor 21 driving the first driving nut 4a is stored in the lower elastic connector 3; when the length of the first piezoelectric stack 51 is shortened until the lower end face of the second driving nut 4b abuts against the second nut support plate 14b, the screw assembly 7 has displaced relatively downwards relative to the initial state, and at this time, a gap exists between the first driving nut 4a and the first piezoelectric stack cover 52, so that the energy in the elastic connector 3 at the lower part is released, the first driving nut 4a is driven to rotate reversely, and the first driving nut 4a moves upwards until the first driving nut 4a recovers to the initial position, that is, the energy in the elastic connector 3 at the lower part is all released; the first piezoelectric stack 51 is then restored in length to the initial state. The above process is an actuation cycle, and during the time that the screw assembly 7 is continuously pressed, the downward displacement of the screw assembly 7 is accumulated by continuously repeating the cycle process, so that the screw 71 moves downward to output the displacement.

The third driving state: when the screw assembly 7 is under tension load, the first driving nut 4a and the second driving nut 4b are driven to move until the upper end face of the first driving nut 4a abuts against the first nut support plate 14a, and the upper end face of the second driving nut 4b abuts against the second piezoelectric stack cover 62; the second piezoelectric stack 61 works, the two driving nuts and the screw assembly 7 are pushed to synchronously move downwards by stretching through the inverse piezoelectric effect, at this time, the frameless torque motor 21 is controlled to drive the first driving nut 4a to rotate forwards by a certain angle, and the screw assembly 7 can only axially move and cannot rotate, so that the first driving nut 4a rotates forwards by a certain angle to move downwards, and the upper end surface of the second driving nut 4b abuts against the second piezoelectric stack cover 62 and cannot rotate, so that energy generated by the frameless torque motor 21 driving the second driving nut 4b is stored in the upper elastic connector 3; when the length of the second piezoelectric stack 61 is shortened until the upper end surface of the first driving nut 4a abuts against the first nut support plate 14a, the screw assembly 7 has displaced relatively upwards relative to the initial state, and at this time, a gap exists between the second driving nut 4b and the second piezoelectric stack cover 62, so that the energy in the upper elastic connector 3 is released, the second driving nut 4b is driven to rotate forward, and the second driving nut 4b moves downwards until the second driving nut 4b returns to the initial position, that is, the energy in the upper elastic connector 3 is completely released; the second piezoelectric stack 61 is then restored in length to the initial state. The above process is an actuation cycle, and during the period that the screw assembly 7 is continuously pulled, the upward displacement of the screw assembly 7 is accumulated by continuously repeating the cycle process, so that the screw 71 moves downward to output the displacement;

fourth drive state: when the screw assembly 7 is under tension load, the upper end surface of the first driving nut 4a abuts against the first female support plate 14a, so that the first driving nut 4a and the second driving nut 4b are driven to move until the upper end surface of the second driving nut 4b abuts against the second piezoelectric stack cover 62; the second piezoelectric stack 61 works, the two driving nuts and the screw assembly 7 are pushed to synchronously move downwards by stretching through the inverse piezoelectric effect, at this time, the frameless torque motor 21 is controlled to drive the first driving nut 4a to reversely rotate, and the screw assembly 7 can only axially move and cannot rotate, so that the first driving nut 4a reversely rotates and then moves upwards until the upper end face of the first driving nut 4a abuts against the first nut supporting plate 14a, and the upper end face of the second driving nut 4b abuts against the second piezoelectric stack cover 62 and cannot rotate, so that energy of the frameless torque motor 21 driving the second driving nut 4b is stored in the upper elastic connector 3; when the length of the second piezoelectric stack 61 is recovered, the upper end surface of the first driving nut 4a abuts against the first nut support plate 14a, so that the first driving nut 4a and the screw assembly 7 cannot rotate, and a gap exists between the second driving nut 4b and the second piezoelectric stack cover 62, so that the energy in the elastic connector 3 at the upper part is released, the second driving nut 4b is driven to rotate reversely, and the second driving nut 4b moves upwards until the upper end surface of the second driving nut 4b abuts against the second piezoelectric stack cover 62. The above process is an actuation cycle, and during the period that the screw assembly 7 is continuously pulled, the downward displacement of the screw assembly 7 is accumulated by continuously repeating the cycle process, so that the screw 71 moves downward to output the displacement.

Therefore, the piezoelectric stacks are arranged at two ends of the device, the device works when the load is downward through the lower piezoelectric stack, and works when the load is upward through the upper piezoelectric stack, so that the operation of the tensile load and the compressive load can be realized, and the device has the advantages of simple structure, convenience in installation and capability of quickly replacing parts.

The above-described embodiments are merely preferred embodiments of the present invention, which should not be construed as limiting the invention. Various changes and modifications may be made by one of ordinary skill in the pertinent art without departing from the spirit and scope of the present invention. Therefore, the technical scheme obtained by adopting the mode of equivalent replacement or equivalent transformation is within the protection scope of the invention.

Claims (8)

1. The bidirectional displacement accumulation piezoelectric stack actuator capable of bearing pulling pressure is characterized by comprising a shell component (1), a motor component (2), two elastic connectors (3), a first driving nut (4 a), a second driving nut (4 b), a first piezoelectric stack component (5), a second piezoelectric stack component (6) and a screw rod component (7), wherein the motor component (2), the two elastic connectors, the second driving nut (4 a), the second driving nut (4 b), the first piezoelectric stack component (5), the second piezoelectric stack component (6) and the screw rod component (7) are coaxially arranged in an inner cavity of the shell component (1);

the motor component (2) is fixed in the middle of an inner cavity of the shell component (1), the first driving nut (4 a) and the second driving nut (4 b) are respectively arranged on two sides of the motor component (2), and the first driving nut (4 a) and the second driving nut (4 b) are respectively connected with the motor component (2) through an elastic connector (3);

the motor assembly (2) can bidirectionally drive a first drive nut (4 a) and a second drive nut (4 b) to rotate around an axis through the elastic connectors (3), each elastic connector (3) has a telescopic freedom degree along the axial direction, and when the drive nut connected with each elastic connector (3) is limited to rotate around the axis and the motor assembly (2) is driven continuously, the elastic connectors (3) also have elastic deformation allowance so as to be capable of being reversely and circumferentially twisted;

one end of the first piezoelectric stack component (5) is fixed on the end wall of one side of the inner cavity of the shell component (1), and the end face of the other end of the first piezoelectric stack component is used as a pressed surface matched with the first driving nut (4 a); one end of the second piezoelectric stack component (6) is fixed on the other end wall of the inner cavity of the shell component (1), and the end face of the other end of the second piezoelectric stack component is used as a compression surface matched with the second driving nut (4 b);

the screw component (7) is arranged in a central channel which sequentially penetrates through the second piezoelectric stack component (6), the second driving nut (4 b), the first elastic connector (3), the penetrating motor component (2), the second elastic connector (3), the first driving nut (4 a) and the first piezoelectric stack component (5), one end of the screw component is used as a displacement output end and extends out of the top of the shell component (1), the other end of the screw component is limited in the axial movement range by a group of limiting components in the inner cavity of the second piezoelectric stack component (6), and the screw component (7) does not have the degree of freedom of circumferential rotation around an axis; the middle part of the screw component (7) is an external thread section, and a first driving nut (4 a) and a second driving nut (4 b) are respectively matched with the external thread section to form a thread pair;

when the displacement output end is under the action of pressure, the first piezoelectric stack component (5) pushes the screw rod component (7) to axially move through inverse piezoelectric effect deformation, the motor component (2) drives the first driving nut (4 a) and the second driving nut (4 b) to operate, the positions of the first driving nut (4 a) and the second driving nut (4 b) are recovered, and the displacement accumulation of the screw rod component (7) is realized through continuous repetition; when the displacement output end is under the action of a tensile force, the second piezoelectric stack assembly (6) pushes the screw assembly (7) to axially move through the deformation of the inverse piezoelectric effect, the motor assembly (2) drives the first driving nut (4 a) and the second driving nut (4 b) to operate, the positions of the first driving nut (4 a) and the second driving nut (4 b) are recovered, and the displacement accumulation of the screw assembly (7) is realized through continuous repetition;

the shell component (1) comprises a first piezoelectric stack shell (13), a motor shell (15), a second piezoelectric stack shell (17), a first nut support plate (14 a) and a second nut support plate (14 b), one end of the motor shell (15) is connected with one end of the first piezoelectric stack shell (13) through the first nut support plate (14 a), and the other end of the motor shell (15) is connected with one end of the second piezoelectric stack shell (17) through the second nut support plate (14 b);

the motor component (2) is fixedly arranged in a motor shell (15), the first piezoelectric stack component (5) and the first driving nut (4 a) are arranged in a first piezoelectric stack shell (13), the second piezoelectric stack component (6) and the second driving nut (4 b) are arranged in a second piezoelectric stack shell (17), the other end of the first piezoelectric stack shell (13) is sealed by a lower bottom cover (11), and the other end of the second piezoelectric stack shell (17) is sealed by an upper bottom cover (16);

the motor assembly (2) comprises a frameless torque motor (21) fixedly connected in a motor shell (15) and a first motor connecting shaft (24) and a second motor connecting shaft (25) fixedly connected to two sides of a rotor inside the frameless torque motor (21) respectively, the output ends of the first motor connecting shaft (24) and the second motor connecting shaft (25) are respectively in interference fit and sleeved with a bearing (26), the two bearings (26) are fixedly installed in the shell assembly (1) respectively, and rotary support is provided for the first motor connecting shaft (24) and the second motor connecting shaft (25).

2. The actuator of claim 1, wherein each of the lower and upper bottom covers (11, 16) comprises a disk for end sealing, and a hollow shaft section and a ball spline in the inner cavity of the housing assembly (1), the hollow shaft section is vertically mounted on the disk at one end and the ball spline is mounted at the other end, and the two polished rod sections of the screw assembly (7) except the middle outer threaded section respectively pass through the ball splines at the sides, thereby limiting the screw assembly (7) to move only in the axial direction but not to rotate and move in the radial direction.

3. The actuator of the bi-directional displacement accumulation piezoelectric stack capable of bearing the pulling and pressing force as claimed in claim 2, wherein the limiting component is two limiting blocks (18), two spaced limiting holes (113) are formed on the hollow shaft section of the lower bottom cover (11), and a limiting block (18) for limiting the axial movement range of the screw rod component (7) is arranged in each limiting hole (113) in an interference manner.

4. The actuator of the bi-directional displacement accumulation piezoelectric stack capable of bearing the pulling and pressing force as claimed in claim 2, wherein each elastic connector (3) comprises a first connector (31) and a second connector (33), the first connector (31) is provided with a plurality of rubber sheets (32) at one end, the inner wall of the second connector (33) is provided with a plurality of stop strips (34) which are the same as the number of the rubber sheets (32) on the first connector (31), and the stop strips (34) are arranged along the axial direction; under the matching state of the first connector (31) and the second connector (33), a rubber sheet (32) which is attached to the inner wall of the second connector (33) is just inserted between every two barrier strips (34) and no gap exists between the barrier strips (34) and the rubber sheet (32), and the first connector (31) can move in the second connector (33) along the axial direction and can be twisted for a certain angle through the deformation of the rubber sheet (32) through the matching of the barrier strips (34) and the rubber sheet (32); in the elastic connector (3) at each side of the motor component (2), the first connector (31) is fixedly connected with the motor connecting shaft at the side for transmission, and the second connector (33) is fixedly connected with the driving nut at the side for transmission.

5. The actuator of the bi-directional displacement accumulation piezoelectric stack capable of bearing the pulling and pressing force as claimed in claim 1, wherein the first piezoelectric stack assembly (5) comprises a first piezoelectric stack (51) and a first piezoelectric stack cover (52) which are fixed in a clamping manner, the second piezoelectric stack assembly (6) comprises a second piezoelectric stack (61) and a second piezoelectric stack cover (62) which are fixed in a clamping manner, and gaps necessary for circumferential deformation are reserved on the inner and outer walls of the first piezoelectric stack (51) and the second piezoelectric stack (61); the second drive nut (4 b) is only axially movable between the second nut support plate (14 b) and the second piezoelectric stack cover (62); the first drive nut (4 a) is only axially movable between the first nut support plate (14 a) and the first piezoelectric stack cover (52).

6. The actuator of the bi-directional displacement accumulation piezoelectric stack capable of bearing the pulling and pressing force as claimed in claim 3, wherein the screw assembly (7) comprises a screw (71) and a first supporting shaft (72) and a second supporting shaft (73) which are fixedly connected to two ends of the screw (71) respectively, the first supporting shaft (72) and the second supporting shaft (73) are both optical axes, and a limit stop ring (74) is connected to the end of the first supporting shaft (72); the screw rod (71) is in threaded connection with the first driving nut (4 a) and the second driving nut (4 b) through external threads, the limiting check ring (74) is located between the two limiting blocks (18), and the tail end of the second supporting shaft (73) is fixedly connected with an external nut (8) extending out of the shell assembly (1).

7. The actuator of claim 6, wherein the second shaft (73) has a second shaft groove (731) for engaging with the ball spline of the side, and the first shaft (72) has a first shaft groove (721) for engaging with the ball spline of the side.

8. A method for actuating the bidirectional displacement accumulation piezoelectric stack actuator according to any one of claims 1 to 7, wherein the bidirectional displacement accumulation piezoelectric stack actuator receives an external load in a direction that a displacement output end faces upwards, and displacement accumulation is carried out by controlling a driving direction of the motor assembly (2) according to a load type and a specified displacement output direction:

when the screw assembly (7) is subjected to pressure load, the first driving nut (4 a) and the second driving nut (4 b) are driven to move until the lower end face of the second driving nut (4 b) abuts against the second nut supporting plate (14 b), and the lower end face of the first driving nut (4 a) abuts against the first piezoelectric stack cover (52); the first piezoelectric stack (51) works, stretches through the inverse piezoelectric effect, pushes the two driving nuts and the screw assembly (7) to synchronously move upwards, controls the frameless torque motor (21) to drive the second driving nut (4 b) to rotate in the positive direction and then move downwards until the lower end face of the second driving nut (4 b) abuts against the second nut supporting plate (14 b), and the lower end face of the first driving nut (4 a) abuts against the first piezoelectric stack cover (52) and cannot rotate, so that energy of the frameless torque motor (21) driving the first driving nut (4 a) is stored in the lower elastic connector (3); when the length of the first piezoelectric stack (51) is recovered, the lower end face of the second driving nut (4 b) is abutted against the second nut support plate (14 b) and cannot rotate, and a gap exists between the first driving nut (4 a) and the first piezoelectric stack cover (52), so that the energy in the elastic connector (3) at the lower part is released, and the first driving nut (4 a) is driven to rotate forward and move downward until the lower end face of the first driving nut (4 a) is abutted against the first piezoelectric stack cover (52); during the continuous compression of the screw assembly (7), accumulating the upward displacement of the screw assembly (7) by continuously repeating the process, so as to move the screw (71) upwards to output the displacement;

when the screw assembly (7) is subjected to pressure load, the first driving nut (4 a) and the second driving nut (4 b) are driven to move until the lower end face of the second driving nut (4 b) abuts against the second nut supporting plate (14 b), and the lower end face of the first driving nut (4 a) abuts against the first piezoelectric stack cover (52); the first piezoelectric stack (51) works, the two driving nuts and the screw assembly (7) are pushed to synchronously move upwards by stretching through the inverse piezoelectric effect, the frameless torque motor (21) is controlled to drive the second driving nut (4 b) to reversely rotate for a certain angle so as to move upwards, the lower end face of the first driving nut (4 a) abuts against the first piezoelectric stack cover (52) and cannot rotate, and therefore energy of the frameless torque motor (21) driving the first driving nut (4 a) is stored in the lower elastic connector (3); when the length of the first piezoelectric stack (51) is shortened until the lower end face of the second driving nut (4 b) abuts against the second nut support plate (14 b), the screw assembly (7) has a relatively downward displacement relative to the initial state, and at the moment, a gap exists between the first driving nut (4 a) and the first piezoelectric stack cover (52), so that the energy in the elastic connector (3) at the lower part is released to drive the first driving nut (4 a) to reversely rotate so as to move upwards until the first driving nut (4 a) is restored to the initial position, namely the energy in the elastic connector (3) at the lower part is completely released; then the length of the first piezoelectric stack (51) is recovered to the initial state; during the continuous compression of the screw assembly (7), accumulating the downward displacement of the screw assembly (7) by continuously repeating the process, so as to make the screw (71) move downward to output the displacement;

when the screw rod assembly (7) is under tension load, the first driving nut (4 a) and the second driving nut (4 b) are driven to move until the upper end face of the first driving nut (4 a) abuts against the first nut supporting plate (14 a), and the upper end face of the second driving nut (4 b) abuts against the second piezoelectric stack cover (62); the second piezoelectric stack (61) works, the two driving nuts and the screw assembly (7) are pushed to synchronously move downwards by stretching through the inverse piezoelectric effect, the frameless torque motor (21) is controlled to drive the first driving nut (4 a) to rotate forward by a certain angle so as to move downwards, the upper end face of the second driving nut (4 b) abuts against the second piezoelectric stack cover (62) and cannot rotate, and therefore energy of the frameless torque motor (21) driving the second driving nut (4 b) is stored in the upper elastic connector (3); when the length of the second piezoelectric stack (61) is shortened until the upper end face of the first driving nut (4 a) abuts against the first nut supporting plate (14 a), the screw assembly (7) has a relatively upward displacement relative to the initial state, and at the moment, a gap exists between the second driving nut (4 b) and the second piezoelectric stack cover (62), so that the energy in the elastic connector (3) at the upper part is released to drive the second driving nut (4 b) to rotate forwards and move downwards until the second driving nut (4 b) is restored to the initial position, namely the energy in the elastic connector (3) at the upper part is completely released; then the length of the second piezoelectric stack (61) is recovered to the initial state; during the continuous tension of the screw assembly (7), accumulating the upward displacement of the screw assembly (7) by continuously repeating the process, so as to make the screw (71) move downwards to output the displacement;

when the screw assembly (7) is under tension load, the upper end face of the first driving nut (4 a) abuts against the first nut supporting plate (14 a), and the first driving nut (4 a) and the second driving nut (4 b) are driven to move until the upper end face of the second driving nut (4 b) abuts against the second piezoelectric stack cover (62); the second piezoelectric stack (61) works, the two driving nuts and the screw assembly (7) are pushed to synchronously move downwards by stretching through the inverse piezoelectric effect, at the moment, the frameless torque motor (21) is controlled to drive the first driving nut (4 a) to reversely rotate so as to move upwards until the upper end face of the first driving nut (4 a) abuts against the first nut supporting plate (14 a), and the upper end face of the second driving nut (4 b) abuts against the second piezoelectric stack cover (62) so as not to rotate, so that energy generated by the frameless torque motor (21) driving the second driving nut (4 b) is stored in the upper elastic connector (3); when the length of the second piezoelectric stack (61) is recovered, the upper end face of the first driving nut (4 a) is abutted against the first nut support plate (14 a) and cannot rotate, and a gap exists between the second driving nut (4 b) and the second piezoelectric stack cover (62), so that the energy in the elastic connector (3) at the upper part is released, and the second driving nut (4 b) is driven to rotate reversely and move upwards until the upper end face of the second driving nut (4 b) is abutted against the second piezoelectric stack cover (62); during the continuous tension of the screw assembly (7), the downward displacement of the screw assembly (7) is accumulated by continuously repeating the process, so that the screw (71) moves downward to output the displacement.

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