Recharge device, particularly for drive mechanisms for extending and withdrawing operative members of a space vehicle

In a spring operated mechanism, the recharge device (1) is adapted to wind the spring (4) during idle times when the drive mechanism (4,16) is not operating. The recharge device has a lever member (48,50) operated by a shape memory alloy member (46) and adapted to turn a gear (8,26) for winding the spring.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a recharge device, particularly for spring 
operated drive mechanisms for extending and withdrawing operative members 
of a space vehicle. 
2. Description of the Prior Art 
Space vehicles require deployment devices adapted to unfold an operative 
member (such as an antenna or a probe, etc.) when they have reached their 
operational orbit, and also to fold it back when necessary. Former types 
of deployment devices were based on spring operated mechanisms, designed 
for "one-shot" operation, and therefore unsuited for modern requirements. 
Deployment devices comprising electrically operated motors were therefore 
designed in order to extend and withdraw an operative member several times 
during the life of the space vehicle. The electrically driven devices, 
though, are heavy, require a complex design and structure, and are not as 
reliable as the spring operated mechanisms. 
This same Applicant designed a spring operated mechanism which combined the 
advantages of simplicity and reliability of "one-shot" mechanisms and the 
multifunctional capability of electrically operated one. 
This type of mechanism, also known by the acronym DARM (Deployment And 
Retraction Mechanism), has been disclosed in U.S. Pat. No. 4,884,464, 
filed by this same Applicant, and substantially operates by drawing 
entirely on the elastic energy stored in a helical spring. Therefore, this 
mechanism can only carry out a limited number of manoeuvres (deployment 
and retraction) according to the maximum energy stored in the spring. 
This fact greatly limits the performance of the DARM of the prior art and 
also limits its advantages over the more traditional electrically driven 
deployment mechanisms. 
The aim of the present invention is to eliminate the disadvantages 
described above in the DARMs and in the spring operated mechanisms of the 
known art. 
SUMMARY OF THE INVENTION 
The above aim, as well as these and other objects that will be more 
apparent later, are achieved by a recharge device, particularly for spring 
operated drive mechanisms for extending and withdrawing operative members 
of a space vehicle, comprising a frame having a spring means, said spring 
means being connected to a shaft, said shaft having a winding direction of 
rotation and an unwinding direction of rotation, in said unwinding 
direction of rotation said shaft turning for operating a drive mechanism 
under the action of sad spring means, in said winding direction of 
rotation said shaft being turned to wind and recharge said spring means, 
characterized in that it comprises at least one actuator having a shape 
memory alloy member adapted to rotate said shaft in said winding direction 
of rotation for recharging said spring means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
With reference to the drawings, a driving mechanism 16 includes a recharge 
device, generally designated by the reference numeral 1, which comprises a 
frame 2 supporting a spiral spring 4, having one end 6 fixed to the frame 
and the other end fixed to a first front toothed wheel 8 associated with a 
shaft, or axle, 12. 
In a per se known manner, as, for example, illustrated in U.S. Pat. No. 
4,884,464, spiral spring 4 is adapted to unwind and therefore to rotate 
shaft 12, which operates the driving mechanism 16. 
A ratchet wheel 10 is keyed to shaft 12, to engage wheel 8 when motion has 
to be transmitted from the spiral spring to shaft 12 and to prevent the 
first wheel 8 from turning clockwise under the action of the spiral 
spring, when shaft 12 is still and the spiral spring is wound, or 
recharged, as explained hereinafter. Spring 4 can wind (recharge) in a 
clockwise direction, with reference to FIGS. 3 and 4. 
First wheel 8 is mounted idle on shaft 12, by means, for example, of a ball 
bearing 18 and is adapted to recharge spiral spring 4 by letting ratchet 
20 run on ratchet wheel 10 associated with the shaft by means of keys 22. 
As illustrated in FIG. 3, rachet 20 is pivotably fixed to wheel 8 by a 
first pin 23. A rachet biasing spring 25 extends from a second pin 27 on 
rachet 20 to a third pin 29 connected to wheel 8. 
A pin 41 is associated with frame 2 and supports a support member 42 
adapted to rotate idle on pin 41, by a limited angle set by the slot 44. 
To this purpose, an adapted grub screw 43 is fixed to the support member 
42 and inserted into slot 44. 
A linear actuator 46 is pivoted at 35 to the support member 42 for rotation 
about an axis 37 and comprises a rod 48 and a slide 50 adapted to slide 
along rod 48. Slider 50 is pivotably connected to a second wheel 26 by 
means of a pin 52 so that, by sliding upward (with reference to FIG. 4) 
along rod 48, slider 50 makes the second wheel 26 rotate clockwise. 
Linear actuator 46 comprises a heater 54 arranged between rod 48 and a 
Shape Memory Alloy spring 56 adapted to actuate slider 50 when heated by 
heater 54. A tension spring 58 is associated with the lower end of the rod 
48 and with slider 52. Heater 54, as illustrated in the drawings, for 
example comprises two PTFE shells 60 mounted on rod 48 and having 
resistance coils made of Constantan wire connected to an electric terminal 
62. The assembly is inserted into a copper pipe 64, on which the SMA 
spring runs during the heating and cooling stages. 
The second front toothed wheel 26 is kept at a set distance from first 
wheel 8 by a spring 24 which biases second wheel 26 against an engagement 
means 28 associated with shaft 12. 
The engagement means, comprises a second linear actuator and is adapted to 
engage the first toothed wheel with second wheel 26. The engagement means 
comprises a bush 30 slidably mounted on shaft 12 which has a ball bearing 
32 on which a second shaft 34 is idle. Bush 30 presses wheel 26 by means 
of a SMA (Shape Memory Alloy) spring 36, which is adjusted by the limit 
stop disk 38, fastened by a nut 40. A heater 39 s arranged between second 
shaft 34 and spring 36. When the SMA spring 36 is heated the spring coil 
dilates and therefore bush 30 pushes the second front toothed wheel 26 to 
engage first wheel 8. 
The operation of the recharge device is as follows. Heater 39 heats SMA 
spring 36 which dilates and pushes bush 30 leftward (with reference to 
FIG. 2). Bush 30 in turn pushes the second front toothed wheel 26 so that 
clutch teeth 45 of wheel 26 engage clutch teeth 47 of the first front 
toothed wheel 8. Although the second wheel is thus engaged, it is idle on 
its shaft and exerts friction on bush 30. 
Heater 54 heats SMA spring 56, of the second linear actuator 46, and slider 
50 slides upwards (from position A to position B of FIG. 4) turning second 
wheel 26, and therefore first wheel 8, clockwise, thereby winding, or 
recharging, spiral spring 4. Ratchet wheel 10 is still during recharging, 
being keyed to shaft 6, while ratchet 20, which is associated with first 
wheel 8, runs clockwise on the ratchet wheel. 
When heaters 39 and 54 cool off, of first and second linear actuators 28 
and 46 respectively, bush 30 moves to the right, biased by spring 24, and 
slider 50 returns to position A, biased by spring 58. During this step 
(when wheels 8 and 26 are disengaged) ratchet wheel 10 and ratchet 20 
prevent second wheel 8 from turning counterclockwise thereby unwinding the 
spiral spring 4. 
By repeating this operation, spiral spring 4 is recharged and, when 
deployment is required, it can be discharged (unwound) letting shaft 12 
free to rotate. Spring 4 therefore turns the first wheel counterclockwise, 
wheel 8 acts on ratchet wheel 10 which, being keyed to shaft 12, rotates 
shaft 12 thereby activating hinge mechanism 16. 
The recharge device can guarantee a recharge motion (from position A to 
position B) of about 80.degree. per cycle. Since, in the illustrated case, 
the DARM spiral spring has a preloading of 1400.degree., i.e. about four 
complete turns, it will of course be necessary to activate the RM 
(Recharge Mechanism) several times in order to obtain a complete recharge 
of the spring. The spiral spring 4 does not have to be completely unwound 
to be recharged again; in fact, it can be recharged in any position it 
reaches between 0.degree. and 1400.degree. and, in this way, the 
consecutive recharging cycles can be reduced. 
It has been seen n practice how the recharge mechanism, according to the 
invention, achieves the intended aim and objects by using shape memory 
alloys, which enable thermal energy to be converted into mechanical 
energy, with a good F/d ratio; where F (N) represents the thrust force 
produced during the change of material force, and d (mm) represents the 
displacement. Of course, both F and d can only be calculated on the basis 
of the alloy storage temperature, which in turn depends on the thermal 
range in which both the DARM and the RM must operate. 
The device according to the invention may have numerous modifications and 
variations, all within the inventive concept; furthermore, all the details 
may be substituted with technically equivalent elements. 
The materials employed, as well as the dimensions, may be any according to 
the specific needs and the state of the art. 
Where technical features mentioned in any claim are followed by reference 
signs, those reference signs have been included for the sole purpose of 
increasing the intelligibility of the claims and accordingly, such 
reference signs do not have any limiting effect on the scope of each 
element identified by way of example by such reference signs.