Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2002-01-08
2002-11-12
Pelham, Joseph (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S200000, C219S202000, C219S521000, C219S385000, C244S137400, C403S028000, C403S404000
Reexamination Certificate
active
06479800
ABSTRACT:
The present invention refers to a remote activation mechanism for equipment regulated deployment or release, being the deployment lineal or rotational. The is specially applicable in deployable antennas and other deployable appendages or ejectable equipment of space vehicles, oceanographic equipment, aeronautics, military equipment, etc., where the elimination of the typical end deployment shock of spring driven deployable systems is mandatory.
Space vehicle deployable appendages acted by means of springs without including any regulation system, one liberated of their hold-down point to begin their deployment, are accelerated in a uncontrolled way until reaching the deployment stroke end stop, on which they impact, transmitting a severe shock to the vehicle main structure. At the end of the deployment, when the appendage reaches the mechanical end stop, the energy stored by the spring has been transferred to the appendage in form of kinetic energy meaning that the appendage has a significant speed when it reaches the deployment end stop. The severe shock transmitted to the structure of the space vehicle can endanger its stability, the structural integrity, the base of the appendage, and also the survival of delicate equipment located close to the appendage, such as electronic and radio-frequency equipment.
Due to that, when a system of springs is used to provide the necessary torque (force if lineal instead of rotational) to deploy an appendage, for example in a space vehicle, a system that reduces the end deployment shock causes by the collision of the appendage against the mechanical end stop, is also implemented. In that way, the maximum deployment speed achieved by the excess of transmitted torque is significantly reduced.
There are several devices dedicated to such a function. They are described immediately afterwards.
a) Eddy current dampers, which are based on the generation of electric currents induced in a copper disk rotating in a magnetic field generated by several couples of magnets located at both sides of the disk. These electric currents induced in the disk cause a torque in the disk proportional to the appendage rotational speed, contrary to the acting motor torque. There is no contact between the disk and the magnets. This system needs that the disk rotates to very high speed, requiring a system that multiplies the appendage deployment speed (e.g. gear train). Those systems have the advantage of not needing electric power supply, but they have important inconveniences such as a significant weight, a great friction torque due to the gear train and a high cost. Additionally, they usually need also external thermal control to be able to operate properly at temperatures below 0° C.
b) Viscous dampers based on forcing a viscous fluid to go by narrow grooves. The flow of viscous fluid passes through the grooves when a difference of pressure between both parts of the grooves is generated. This difference of pressure provides a resistive torque proportional to the appendage rotational speed, contrary to the acting motor torque. These systems have the inconvenience that their behaviour changes significantly with the temperature due to the variation of the fluid viscosity. Additionally, those kind of devices also have associated a high risk of contamination due to the possibility of leakage of the fluid out of its cavity, mainly in operation due to the significant increment of pressure that has to undergone this fluid. The leakage of the fluid could mean the loss of damping behaviour, increasing the risk of the appendage overload in the deployment when the deployment is carried out after a considerable time from the assembly of the viscous damper. A particular kind of viscous damper are those using material of low melting temperature material instead of a viscous fluid (e.g. paraffin, alloys of low melting point, . . .). That is to say that the material needs an energy contribution to start the deployment in order to reach its liquid state, allowing the appendage to start its deployment. Once the material melts, it behaves as a viscous damper. As in those devices the melting temperature is above the operational temperature range of the system, the provided damping is more repetitive. Those systems have the inconvenience of the necessary energy contribution to fuse the whole low melting alloy material and also the loss of heat though the elements forming the cavity containing the material to be melted.
c) Friction dampers based on the generation of friction forces that cause a resistive torque proportional to the appendage rotational speed, contrary to the acting motor torque. This friction force is generated by some brake shoes that contact with a cylindrically disposed friction pad. Shoes and pad get in contact due to the centrifugal force that acts on the rotating shoes. Therefore, the more the rotational speed, the more the centrifugal force on the shoes against the friction pad, the more the force in the contact, and the more the friction force. Those systems need high rotation speed, requiring an additional device that multiplies the appendage deployment speed (e.g., gear train). This system has the advantage of not needing electric power supply, but it has important inconveniences such as the variability of the friction coefficient, and a great friction torque due to the gear train. Additionally, it usually needs also of external thermal control to be able to operate properly at temperatures below 0° C.
There is another system to reduce the end deployment shock based on the absorption of the kinetic energy at the end of deployment by deforming plasticity a metallic piece of honeycomb with its cells vertically faced to the appendage movement. In fact it is a semirigid end stop. Their main inconveniences are its lack of precise positioning of the appendage at the end of deployment, and its capacity to absorb only a part of the total energy (not enough in most cases).
In order to solve the inconveniences of the described devices it was thought of a simple, economic and reliable device able to regulate the movement of a deployable appendage, maintaining their deployment speed inside reasonable limits as to make that the shock at the deployment end is minimum, eliminating the risk of damaging the space vehicle. This would mean a substantial improvement of the spring driven deployable systems. This device should have the following characteristics.
a) Minimum internal friction during operation
b) Non contaminating
c) Conceptual simplicity and simple operation
d) Reliable
e) Light
f) Reusable
g) Easy rearming without dismounting it from its location, without necessity of electric disconnection, eliminating the risks associated with the assembly and disassembly.
h) Electrical redundant activation, if necessary.
i) Long life without degradation.
j) Cheap
In order to solve most of the identified inconveniences of the existing devices the use of any gear train has been avoided to reduce its internal friction and to increase its reliability. Also, the use of non metallic viscous fluids has been rejected in order to avoid any risk of contamination.
It was identified that the advance speed (lineal or rotational) could be directly related with the speed a low melting temperature material band fuses. For doing that, the heat flow to be transmitted to the low melting temperature alloy should be concentrated in the point of the band that blocks the movement, and therefore in the area of the band that is direct load path. Obviously, this material should have its melting point sufficiently low as to maintain reasonably low the necessary energy contribution.
The use of metallic alloys of low melting point was chosen for the melting band due to the following reasons.
a) No outgassing in vacuum conditions.
b) There are several low melting temperature metallic alloys with different melting points.
c) Their thermal conductivity is much lower than the metallic piece pressing on it (cooper).
d) Their latent heat of fusion is reasonably high as to avoid a quick melt of the fusible alloy.
e)
Bueno Ruiz Jose Ignacio
Vazquez Mato Javier
Ostrolenk Faber Gerb & Soffen, LLP
Pelham Joseph
Sener, Ingenieria Y Sistemas, S.A.
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