CN1827475A - Miniature large load SMA space synchronous unlocking mechanism - Google Patents

Abstract

The invention relates to a micro large load SMA space synchronous unlocking device, which uses the split nut device whose bottoms are connected. Wherein, the upper of split nut contains screw to match the bolt and fixed on upper connector via the bolt; the bottoms of split nut are connected via the base to be fixed on the lower connector; the upper edge of split nut has a positioning ring, which support the split nut for circular limit in normal mounting state to conform the tight match with split nut; the upper end of spring supports positioning ring while lower end is supported by base to be compressed state; one end of SMA wire is connected to the positioning ring while another end is fixed on the base; the spring and the driving element as SMA wire are matched to be utilized; in normal mounting state, the force of spring is higher than SMA wire to straighten the SMA wire while in working, the SMA wire is electrically heated, the force of SMA wire is higher than the force of spring, and the SMA wire will constrict to move the positioning ring downwards to release the limit on split nut, to complete the space unlocking function of said device. The invention can unlock quickly to meet the demand of synchronization, with small volume and light weight.

Description

Miniature large load SMA space synchronous unlocking mechanism

technical field

The invention relates to a space unlocking structure, in particular to a SMA space synchronous unlocking mechanism with a miniature large load (namely 20000N).

Background technique

The spacecraft needs a variety of separation and unlocking mechanisms to complete the space unlocking function, for example, the separation from the launch vehicle, the space deployment of large solar panels and other accessories on the satellite, etc. This separation and unlocking mechanism has two main functions: on the one hand, it protects the payload during launch and prevents it from being unlocked by the launch load; etc., quickly release the payload on the flight track to realize the unlocking function. In order to ensure the connection, in some cases, the spacecraft uses more than one unlocking mechanism, and the synchronization of the mechanism unlocking is another important factor affecting the separation of the connected parts.

With the emergence of a new generation of small satellites, the internal and external components of satellites are closer to vibration and pollution sources, so it is inevitable to develop a low-vibration, pollution-free space unlocking mechanism. In the study of low-vibration space unlocking mechanism, a main focus is to apply the shape memory properties of shape memory alloy SMA to realize the space unlocking function. SMA materials can return to the shape of the high-temperature parent phase when heated, resulting in a strain of about 6% and a huge recovery force. Therefore, NASA NASA and some famous commercial companies have carried out research on a new type of space unlocking structure using SMA as a mechanical drive element, including Darin Mckinnis, Fastening Apparatus Having Shape Memory AlloyActuator, NASA Johnson Space Center, MSC-21935 -1., introduced NASA's space unlocking mechanism, which uses SMA rods as the driving element of the unlocking mechanism. The piston 54 is located in the fixed sleeve, its lower part is in contact with the SMA rod 24 , and its inner part is in contact with the split nut 72 . The split nut is composed of nuts that are divided into three parts in the circumferential direction, fixed with the piston by pin 78, as shown in the A-A sectional view in Figure 2, in the connected state, the bosses 68, 70 of the piston and the bosses 74, 76 of the split nut Cooperate, under the action of the piston, each part of the split nut is in close contact, forming a complete thread inside, the washer 92 is fixed on the fixed sleeve, and has the effect of axially limiting the split nut, and the bolt 26 passes through the upper connecting piece 36 is connected with the split nut, thereby realizing the connection and fixation of the two parts; when the separation is unlocked, the SMA rod is energized to heat the unlocking mechanism, the SMA rod is extended, the pin is cut off, and the driving piston is moved up, and the distance moved up is exactly the split nut The width of the step makes the bosses 68, 70 of the piston disengage from the bosses 74, 76 of the split nut, the radial restraint of the split nut is released, each part is opened outward, and the connecting bolts are released, so as to realize up and down The separation between the connectors is unlocked.

Although NASA's space unlocking mechanism can be reused, its disadvantages are: (1) It needs to be reassembled and the operation is complicated; (2) The unlocking time is long and cannot meet the synchronization requirements; (3) In order to ensure the connection and bearing, its The volume and mass are relatively large, and it is not suitable for space unlocking of small and large loads.

Contents of the invention

The technical solution of the present invention is to overcome the deficiencies of the prior art, and provide a miniature large-load SMA space synchronous unlocking mechanism with small volume and light weight, which can be quickly unlocked and can meet the requirement of synchronization.

The technical solution of the present invention: a miniature large-load SMA space synchronous unlocking mechanism, which is characterized in that it adopts a split nut structure connected at the bottom, and there are threads in the upper part of the split nut, which are connected with bolts and fixed on the top by bolts. On the connector, the bottom of the split nut is connected together and fixed on the lower connector through the base. There is a positioning ring on the upper part of the split nut. In the normal installation state, the positioning ring supports the split nut for circumferential restraint to ensure the split The valve nut is tightly closed, and the positioning ring is positioned axially by the spring and the SMA wire. The upper end of the spring supports the positioning ring, and the lower end supports the base to make it in a compressed state. One end of the SMA wire is connected to the positioning ring, and the other end is fixed on the base. The spring It is paired with the driving element SMA wire. In the normal installation state, the force of the spring is greater than that of the SMA wire to straighten the SMA wire. When working, the SMA wire is energized to heat the SMA wire. The force of the SMA wire is greater than the force of the spring, and the SMA wire shrinks to drive the positioning ring. Move down to release the constraint on the split nut and release the bolt, thus completing the space unlocking function of the mechanism.

The present invention mainly uses the SMA material to return to the shape of the high-temperature parent phase when heated, and generates about 6% strain and huge restoring force to realize the unlocking of the mechanism; utilizes the characteristics of the SMA material's low yield stress at low temperature and high yield stress at high temperature, and The spring fit realizes the reusable function of the mechanism. In the installation state (low temperature), the spring force is greater than the yield force of the SMA wire at low temperature, and the SMA wire is in a tensioned state under the action of the spring force, and the spring presses the positioning ring to ensure that the split nuts are tight. Electric heating (high temperature), at this time the recovery force of the SMA wire is greater than the spring force, the SMA wire shrinks, drives the positioning ring to move down, compresses the spring, releases the constraint on the split nut, and releases the bolt, thereby completing the space unlocking function of the mechanism. After power-on, the temperature drops, and the low-temperature yield force of the SMA wire is less than the spring force. Under the action of the spring force, the SMA wire is elongated, and the positioning ring returns to the original position, realizing the reusable function of the mechanism.

Compared with the prior art, the present invention has more advantages in terms of volume, quality, synchronization, etc., and can better meet the stringent requirements of aerospace equipment for volume and quality, which are specifically manifested in the following aspects:

(1) The split nut structure connected at the bottom simplifies the mechanism design, has a simple structure and high reliability;

(2) The installation size of the present invention does not exceed Ф30mm, as shown in Figure 7, with small volume and light weight;

(3) The present invention directly energizes and heats the SMA wire, while the prior art uses electricity to heat the resistance rod, and then heats the SMA rod through the resistance rod. Compared with the two, the heating time required by the present invention is shorter and the unlocking is faster ;

(4) Tests show that under the action of a DC voltage of 28V, the mechanism is separated and unlocked within 0.1s of the present invention, which can better meet the synchronization requirements of the mechanism;

(5) The present invention adopts SMA wires and springs to cooperate to pull the positioning ring, which can automatically restore the original structure. In the prior art, it needs to be reassembled before it can be used again. Therefore, the present invention is more convenient for repeated use on the ground.

Description of drawings

Figure 1 is a schematic structural diagram of NASA's space unlocking mechanism;

Fig. 2 is A-A sectional view of Fig. 1;

Fig. 3 is the outline drawing of the piston and split nut of NASA;

Fig. 4 is the assembly structure schematic diagram of the present invention;

Fig. 5 is a three-dimensional schematic diagram of the internal structure of the present invention;

Fig. 6 is a structural schematic diagram of a split nut connected at the bottom of the present invention;

Fig. 7 is a schematic diagram of installation dimensions of the present invention;

Fig. 8 is a schematic diagram of the installation length of the SMA wire of the present invention.

Detailed ways

As shown in Figures 4 and 5, the present invention is composed of SMA wire 2, spring 3, split nut 4, bolt 5, positioning ring 7, and base 8. The present invention is fixed on the lower connector 1 by threads, and the lower part of the split nut 4 It is connected with the base 8 through threads, and the upper part is positioned circumferentially by the positioning ring 7, and fixed with the upper connecting piece 9 by the bolt 5, thereby completing the connection of two adjacent parts. Split nut 4, as shown in Figure 6, is made up of three parts distributed evenly along the circumferential direction, the bottom is connected, and there is expansion screw 6 inside, can adjust the size that split nut 4 opens by expansion screw 6. The lower end of the spring 3 is in contact with the base 8, and the upper end is in contact with the positioning ring 7, and is in a compressed state, pressing the positioning ring 7 to ensure the circumferential positioning of the positioning ring 7 to the split nut 4, so that the split nut 4 is closed in the assembled state, As shown in Figure 4. The upper end of the SMA wire 2 is connected with the positioning ring 7, and the lower end is fixed on the base 8, and is in a tensioned state under the action of the spring force. When the SMA wire 2 is energized to realize the unlocking function, considering the insulation of the SMA wire 2, the positioning ring 7 is made of insulating material, and the connection between the SMA wire 2 and the base 8 is mechanically stopped by the insulating material.

In the design of the embodiment of the present invention, the NiTi alloy wire with a Ti content of 50% and a diameter of 0.5mm in the SMA alloy system is used as the mechanism unlocking drive element. When energized and heated, the actuating distance of the SMA wire 2 is mainly related to two factors: The original length of the wire and the amount of plastic pre-stretch deformation of the wire at low temperature. The longer the original length of the SMA wire 2 and the larger the amount of plastic pre-stretching deformation, the larger the shrinkage distance of the alloy wire when heated. Considering the size requirements of the mechanism design and the shrinkage distance of the SMA wire 2 required for unlocking, the effective installation length of the SMA wire with a pre-stretching deformation of 8% is calculated to be 50 mm, as shown in Figure 8.

The design of spring 3 needs to meet two requirements: (1) The installation state at low temperature, the spring force should be greater than the yield force of the SMA wire at low temperature, so as to ensure that the SMA wire can return to the shape deformed at low temperature under the action of the spring force after power-on (Realize the function that the mechanism can be used repeatedly); (2) under high temperature, it is heated by electricity, and the spring force is smaller than the restoring force of the SMA wire 2 at high temperature, so that the SMA wire 2 can overcome the spring resistance and shrink (realize the unlocking function of the mechanism). The low-temperature yield force and high-temperature recovery force of the SMA wire were determined through experiments, the spring stiffness coefficient k=20N/mm was determined by calculation, and the preload of the spring 3 in the installed state was 200N.

The working process of the present invention: in the installed state, the position of the positioning ring 7 is shown in Figure 4. When the control system issues an unlocking command, the energized SMA wire 2 shrinks, and the positioning ring 7 moves down accordingly, compressing the spring 3, and releasing the release. The circumferential restraint of the petal nut 4, the split nut 4 is loosened along the circumferential direction, the restraint of the bolt 5 is released, the two adjacent parts are unlocked and separated, and the design function of the mechanism is completed. After power-on, the positioning ring 7 moves up under the spring force of the spring 3, and the SMA wire 2 returns to the length in the assembled state, and restores the original structure, so that the next connection and unlocking can be performed.

Claims (4)

1, mini-sized large-load SMA space synchronous unlocking mechanism, it is characterized in that: the distinguish nut structure that adopts the bottom to link together, distinguish nut (4) has screw thread in the top, be connected with bolt (5), and be fixed on the upper connector (9) by bolt (5), the bottom of distinguish nut (4) links together and is fixed on down on the attaching parts (1) by base (8), distinguish nut (4) top steady ring (7) circumferentially arranged, under conventional installing condition, steady ring (7) supports distinguish nut (4) and circumferentially retrains, guarantee that distinguish nut (4) fits, steady ring (7) relies on spring (3) and SMA silk (2) to carry out axial location, steady ring (7) is supported in spring (3) upper end, the lower end is supported in base (8), make it be in compressive state, SMA silk (2) one ends link to each other with steady ring (7), the other end is fixed on the base (8), spring (3) and driver element SMA silk (2) pairing are used, under the usual installing condition, the power of spring (3) is greater than SMA silk (2), make SMA silk (2) stretching, when work, energising heating SMA silk (2), the power of SMA silk (2) is greater than the power of spring (3), and SMA silk (2) shrinks drive steady ring (7) and moves down, and removes the constraint to distinguish nut (4), discharge bolt (5), thereby finish the space unlocking function of mechanism.

2, mini-sized large-load SMA space synchronous unlocking mechanism according to claim 1 is characterized in that: described steady ring (7) is an insulating material.

3, mini-sized large-load SMA space synchronous unlocking mechanism according to claim 1 is characterized in that: described SMA silk (2) and base (8) be connected the mode that adopts the insulating material mechanical stop.

4, mini-sized large-load SMA space synchronous unlocking mechanism according to claim 1 is characterized in that: swell fixture (6) is arranged, by the open size of distinguish nut (4) under expansion spiral shell (6) the nail adjusting work state in the described distinguish nut (4).

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