Improved expulsive separation apparatus

Abstract: An electro-expulsive apparatus (11) including at least two superposed, flexible flat, separately jacketed continuous ribbons (16) of metallic electrical conductor disposed within a sealed outer jacket (12) so that portions of said separately jacketed electrical conductors are separable within said outer jacket (12) to create a void (37,38) when said conductors are energized simultaneously by an electrical current. The disclosure also includes restoring means for returning the separated conductors to rest position and a method of expulsing solid or frangible material.

Description: FIELD OF THE INVENTION The present invention relates to an electro-expulsive device comprising: a flexible blanket having first and second outer walls, at least two separable electrical conductor means enclosed within said blanket, said conductor means having a first position defining a rest position and a second position defining an energized position, an intermediate layer sandwiched between said conductor means, elastic connector means within said blanket for joining the first and second walls to said intermediate layer at spaced intervals whereby said conductor means are separable in accordance with a predetermined pattern under control of said connector means in response to repelling forces created by a magnetic field developed when said electrical conductor means are energized by an electric current, and insulating means provided to support the creation of voids when said repelling forces are generated. BACKGROUND OF THE INVENTION Such an electro-expulsive device is known from US-A-4.690.353. The known apparatus provides an electro-expulsive device by which solid or frangible matter such as ice may be shed from the device by forcing a current to flow through the separable conductor means. The creation of voids is supported by the insulating means which are present within these voids and which do not bond to the material of the outer walls. During manufacturing of the known device several thin release films are inserted between the conductor means at the locations where the voids are desired. SUMMARY OF THE INVENTION It is an object of the present invention to provide an electro-expulsive apparatus for shedding (separating) solid or frangible matter such as ice from the apparatus at low voltage, which apparatus is easy to fabricate and has a long operational life. Therefore, the electro-expulsive device according to the invention is characterized in that said insulating means comprises a first and a second insulating layer, the first insulating layer being arranged between said intermediate layer and the first wall and the second insulating layer being arranged between said intermediate layer and the second wall, said first and second insulating layer are continuous except for several first perforations in the first insulating layer and for several second perforations in the second insulating layer, respectively, the first and second perforations being grouped in rows extending in the longitudinal direction of the conductor means and adjacent to said conductor means, said connector means comprise first connector means which extend through the first perforations and second connector means which extend through the second perforations, respectively. In such a blanket the connector means through the perforations are, advantageously, accomplished by controlled heating and melting of the thermoplastic resin of the blanket so that molten resin flows into the respective perforations thereby joining the outer walls with the intermediate layer as described. In a first preferred embodiment said first perforations in said first insulating layer are offset longitudinally relative to the second perforations in said second insulating layer. By applying these measures a periodically varying spring gradient in the longitudinal axis of the conductor runs is provided. The periodic variation of the spring gradient creates a mild serpentine or sinusoidal deformation in the longitudinal dimension of the outer conductor, which supports to achieve minimal stress throughout the conductor of the outer layer and therefore supports the effective life of the conductor and the blanket. In a second preferred embodiment the conductor means comprises first and second conductor means, which run on opposite sides of the intermediate layer and the first conductor means is in direct contact with the first insulating layer and the second conductor means is in direct contact with the second insulating layer. Preferably, the insulator means are thermal and electrical insulators fabricated of a thermoplastic polymer having a melting point greater than the melting point of the thermoplastic polymer from which the blanket, the connector means and the intermediate layer are fabricated. The first and second conductor means may each define at least one generally flat, continuous ribbon patterned to define elongated ribbon portions spaced by intervening elongated gaps, while the connector means may be spaced along said ribbon portions and may be disposed in said intervening gaps. The electric current supplied to the conductor means, preferably, has such a shape that a force of sufficient magnitude is generated to expulse solid or frangible material bonded to the surface of the electro-expulsive device during a time interval of 10 to 80 microseconds. Long operating life is achieved by taking advantage of a little known property of elastomeric materials (such as polyurethane, polyethylene and butadiene) from which the blanket and the intermediate layer are fabricated. The beneficial property is that initially (during the first 80 micro-seconds of an applied force) the effective modulus of compression (Young's Modulus) of such elastomeric materials is much greater than the modulus values assigned in the usual and customary specifications contained in standard chemical handbooks and chemical dictionaries. That is, initially, the materials are virtually solid. The invention takes advantage of this property by applying a very high current to the conductors of the blanket for a very short time and thereby forcing the surface of the blanket to move almost exactly the same distance as the internal conductor has moved. The initial high modulus of the elastomer makes it almost incompressible in the short term giving the blanket surface a gain motion in a ratio of nearly 1 to 1 relative to the corresponding surface motion of the underlying conductor. The extremely high force, with minimal motion, fractures the crystalline ice (or other frangible material) at the blanket surface and destroys the bond between the ice and the blanket. Mind velocity or gravity then cause the ice to be shed. A method of expulsing solid or frangible material bonded to a surface may comprise the steps of impacting the material abruptly with a force of sufficient magnitude to break the bond between the material and the surface, and, sustaining the force for an interval ranging from 10 to 80 microseconds. The very short pulse contributes to blanket life by limiting the motion required to successfully de-ice. In the earliest portions of the expulsive pulse little metal (copper) or elastomer deformation takes place. Since fatigue damage to both materials is strongly related to total material deformation, the shortened pulse is not only efficient of energy, but provides extended life for all blanket geometries by reducing fatigue damage per cycle. By means of the device according to this invention a long, narrow, thin (0,76.10⁻³ m (0,030 inch) to 2,03.10⁻³ m (0,080 inch) thick) blanket geometry is provided wherein all electrical connections between electronics and blanket are made at one end. This improvement drastically reduces the weight of the leads required to connect blankets to electronics. Blankets are made in long, narrow strips for convenience. To cover a particular surface, multiple segments are laid out side by side with their long dimensions abutting. After these segments have been affixed to the surface to be protected, a thin covering or coating layer of adhesive tape such as polyethylene, a conformal layer of metallic foil or a spray coating of filler material is applied over all the segments to provide a smooth continuous outer surface. All segment connections are at the narrow end. The driver electronics are placed so as to be closest to the connection end. In the case of prior art multiple rectangular segments, harness connection must be made at increasingly large distances as segments get further from the electronics which fires them. In the layout of the present invention, the harness length is minimized which in turn minimizes weight. By means of the device of this invention low ice shedding threshold voltage is provided while at the same time long operational blanket life is obtained. This is achieved by controlling the local spring rate throughout the active region of a blanket segment. Inherently the spring rate varies in the space between blanket wall connector means so that blanket deformation varies; correspondingly, the metallic conductor deformation varies. The result of locally controlled spring rates is to provide non-uniform dynamic conductor deformation and therefore non-uniform blanket deformation during the time when the blanket is fired. This leads to long life of the total apparatus. When the blanket is fired and the upper and lower conductors are repelled from each other, their motion is resisted by two major restoring forces. Since the unbonded voids (between blanket wall connector means) trap no air, static pressure resists conductor separation. Additionally, the elastomeric material which connects upper and lower blanket walls (connector means) stretches and acts as a spring to provide a restoring force. In particular, it is desirable to provide a non-linear spring gradient between top and bottom (outer) walls of the blanket. Initially, the gradient should be nearly zero so that all energy is converted into momentum of the outer (top) conductor and its mating wall. As the outer conductor separates from the inner conductor, the repulsive force diminishes because of the increased distance and because the current decreases as the discharging capacitor voltage decreases. When this occurs, increased spring gradient helps to restore the blanket to its rest condition. As stated earlier, in order to achieve a long blanket fatigue life it is necessary to provide minimal stress throughout the conductor of the outer layer. By providing a periodically varying spring gradient in the longitudinal axis of the conductor runs, the required stress distribution is achieved. The periodic variation creates a mild serpentine or sinusoidal deformation in the longitudinal dimension of outer conductor. This is desirable for two reasons. First, the long, narrow serpentine configuration of the conductor prevents lateral bowing and subsequent fatigue (If lateral bowing occurs then excess stress will occur at the side edges of each longitudinal conductor run). Second, the ripple effect on the surface of the blanket aids in breaking the ice-blanket bond. A preferred means of achieving this type behavior is by bonding the top (outer) wall of the blanket to the bottom (outer) wall of the blanket using an intermediate layer of elastomeric material disposed between the top and bottom walls. This intermediate layer is bonded to top and bottom walls through offset perforations or holes in two separating high melting thermo-electric insulators. By using an intermediate layer bonded alternately to the inner and outer walls, two important functions are achieved. As the conductors separate, the intermediate layer is stretched because of its connection through said perforations to the top and bottom walls. This spring effect is not uniform (from perforation to perforation) in the forces it exerts on the conductors. A first set of perforations in a first insulator permit a connection from the bottom wall to the intermediate layer. A second set of perforations in a second insulator, preferably offset from said first set of perforations, permit a connection between the top wall and the intermediate layer. When the top conductor begins to accelerate away from the bottom conductor the restoring force is greatest in the region of the intermediate layer connection. This periodically varying restoring force creates the required serpentine deformation of the outer conductor. Other features and advantages of the present invention will become more apparent from an examination of the succeeding specification when read in conjunction with the appended drawings, in which; BRIEF DESCRIPTION OF DRAWINGS Figure 1 is a plan view of a preferred embodiment of the improved expulsive blanket of the present invention; Figure 2 is a plan view, enlarged, of a portion of the blanket of Figure 1 showing distribution of perforations in the electro-thermal insulation means; Figure 3 is a vertical section of Figure 1 in the plane of the line 3-3 and in the direction of the arrows showing distribution of conductor means; Figure 4 is a view of a portion of Figure 3 enlarged for clarity; Figure 5 is a vertical section of a portion of Figure 2 in the plane of the line 5-5, enlarged, showing the blanket in a rest position; Figure 6 is a view similar to Figure 5 showing the blanket in the energized position; Figure 7 is a schematic drawing showing the preferred arrangement of a plurality of blankets relative to the electrical harness and control box. DETAILED DESCRIPTION OF THE INVENTION Referring to Figures 1, 2, 3 and 4 the reference numeral 11 designates an expulsive separation apparatus comprising a blanket 12 of thermo plastic material such as polyurethane, polyethelyne and butadiene enclosing elongated continuous ribbon-like conductor means 13 and 14. The conductor means 13 and 14 include ribbon portions 16 with intervening spaces 17, and top conductor means 13 is aligned generally with bottom conductor means 14. As is most apparent in Figure 4 each conductor means 13 and 14 comprise stacks of flat metallic continuous ribbons indicated generally by the reference numerals 18 and 19 respectively. The ribbons 18 and 19, in the disclosed embodiment, are three in number and range in thickness from 25,4.10⁻⁶ m (0,001 inches) to 25,4.10⁻⁵ m (0,010 inches). It is to be understood that although the ribbons of the present disclosure are fabricated of copper, it is anticipated that other suitable electrical conductors may be substituted. In addition, the ribbon stacks 18 and 19 may comprise single or multiple layers. Each ribbon portion of each stack are joined as at 20 (Figure I) and includes a tab portion such as at 21, facilitating a spot electrical connector 22 providing electrical continuity between top conductor means 13 and bottom conductor means 14. Top conductor means 13 is connected to positive lead 23 and bottom conductor means 14 terminates at negative lead 24. As is most apparent in Figures 4, 5 and 6, the polyurethane of blanket 12 surrounds the conductor means 13 and 14 so as to define a first outer wall 26, a second outer wall 27 and an intermediate layer 28. The main body of the conductor means 13 and 14 are isolated further by insulation means defining two layers 29 and 31 of high melting thermoplastic material such as TEFLON (tetrafluoroethylene). It is preferred that the blanket 12 be fabricated of thermoplastic material of low melting point relative to the melting point of the insulator means. The insulating layers 29 and 31, generally coextensive with the area occupied by the conductor means 13 and 14, are formed with perforations. Insulating layer 29 is formed with perforation 32 and insulating layer 31 is formed with perforation 33. The perforations 32 and 33 are offset from one another along the longitudinal axis of the blanket 12 and fall with the spaces or gaps 17 between ribbon stacks as shown in Figures 2 and 4. This disposition of the perforations in insulating layers 29 and 31 makes it possible to provide connector means between the first outer wall 26 and the intermediate layer 28, and between the second outer wall 27 and the intermediate layer 28. The connector means is defined further by the pillars or posts 34 and 36, respectively. This connection is accomplished by controlled heating and melting of the thermoplastic resin of the blanket 12 so that molten resin flows into the respective perforations 32 and 33 thereby joining the outer walls with the intermediate layer in the fashion described above. The high melting electrical and thermal insulating layers 29 and 31 preclude welding between the outer walls and the intermediate layer except at the location of the perforations. Thus, the first outer wall 26 is joined to the intermediate layer 28 by posts 34 and the second outer wall 27 is joined to the intermediate layer 28 by posts 36, as is apparent in the enlarged fragmentary sectional view of Figures 5 and 6. In Figure 5 a blanket segment is shown in the at rest position secured to a surface S, such as the wing of an aircraft, with the second outer wall 27 abutting the surface S and the first outer wall 26 exposed to weather W. Periodically the conductor means are energized causing conductor means 13 and 14 to repel one another under control of the posts 34 and 36. The inherent elasticity (elastic memory) in the thermoplastic material from which the posts are fabricated permits the posts to elongate and to provide a restoring force returning the blanket to the rest position of Figure 5 when the conductor means are de-energized. The restoring force is enhanced by the action of static pressure against the vacuum created in voids 37 and 38 when the blanket is energized. Thus, when the conductor means 13 and 14 are energized, the outer conductor means 13 assumes a serpentine configuration (Figure 6) causing accumulated solid or frangible matter such as ice to be shattered breaking the bond between the ice, the outer wall 26 whereupon the ice disappears due to the force of gravity and the action of air currents sweeping over the wall 26. It is anticipated that the blanket apparatus of the present invention can be fabricated of any desired length, with a variety of configurations of the conductor means, using any suitable conductive material, and blanket material so long as the thermal and electrical insulation means (29 and 31) operates to permit separation of the blanket walls in the fashion described and disclosed. It is preferred that the thickness of the composite blanket be thin and blankets having a thickness ranging from 0,76.10⁻³ m (0,030 inches) to 2,03.10⁻³ m (0,080 inches) operate in satisfactory fashion. As indicated in Figure 7, the long narrow configuration of blankets B minimizes electrical harness requirements and makes it possible to have a short span between the control unit and the blanket pattern. Further advantages and various applications of the principles of the present expulsive blanket invention are the following: 1. Use multiple layers of expulsive blanket to transfer significant momentum to a solid object. This development would allow replacement of pyrotechnic squibs now used to fire under wing missiles. 2. Use of blankets as an integral part of liquid phase heat exchangers such as are used in "peak shaving" systems to minimize peak electrical loads in large air conditioning system. The systems in general, freeze water in off hours and melt it during peak hours. Blankets would keep the freezer coils ice free and allow more efficient operation. 3. Use the impulse nature of the output force to fracture coal along existing fault lines. 4. Use the impulse nature of the output force to create a shock wave in a pipe and thereby kill microbes that would otherwise require chemical treatment to destroy. 5. Use the impulse nature of the output force to create a pressure pulse in front of an non-symmetrical orifice so as to create net flow in one direction. 6. Use the impulse nature of the output force to create atomized liquids for use in a variety of coating processes. It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible of modification of form, size, arrangement of parts and details of operation. The invention rather is intended to encompass all such modifications which are within the scope defined by the claims.

Claims: An electro-expulsive device (10) comprising: a flexible blanket (12) having first and second outer walls (26, 27), at least two separable electrical conductor means (13, 14) enclosed within said blanket, said conductor means (13, 14) having a first position defining a rest position and a second position defining an energized position, an intermediate layer (28) sandwiched between said conductor means (13, 14), elastic connector means (34, 36) within said blanket (12) for joining the first and second walls (26, 27) to said intermediate layer (28) at spaced intervals whereby said conductor means (13, 14) are separable in accordance with a predetermined pattern under control of said connector means (34, 36) in response to repelling forces created by a magnetic field developed when said electrical conductor means are energized by an electric current, and insulating means (29, 31) provided to support the creation of voids when said repelling forces are generated characterized in that said insulating means (29, 31) comprises a first (29) and a second (31) insulating layer, the first insulating layer (29) being arranged between said intermediate layer (28) and the first wall (26) and the second insulating layer (31) being arranged between said intermediate layer (28) and the second wall (27), said first (29) and second (31) insulating layer are continuous except for several first perforations (32) in the first insulating layer (29) and for several second perforations (33) in the second insulating layer (31), respectively, the first (32) and second (33) perforations being grouped in rows extending in the longitudinal direction of the conductor means (13, 14) and adjacent to said conductor means (13, 14), and said connector means comprise first connector means (34) which extend through the first perforations (32) and second connector means (36) which extend through the second perforations (33), respectively. An electro-expulsive device (10) according to claim 1 characterized in that said first perforations (32) in said first insulating layer (29) are offset longitudinally relative to the second perforations (33) in said second insulating layer (31). An electro-expulsive device (10) according to claim 1 or 2 characterized in that the conductor means comprises first (13) and second (14) conductor means, which run on opposite sides of the intermediate layer (28) and the first conductor means (13) is in direct contact with the first insulating layer (29) and the second conductor means (14) is in direct contact with the second insulating layer (31). An electro-expulsive device according to any of the preceding claims, characterized in that the first (29) and second (31) insulator means are thermal and electrical insulators fabricated of a thermoplastic polymer having a melting point greater than the melting point of the thermoplastic polymer from which the blanket (12), the connector means (34, 36) and the intermediate layer (28) are fabricated. An electro-expulsive device (10) according to any of the preceding claims, characterized in that the first (13) and the second (14) conductor means each define at least one generally flat, continuous ribbon patterned to define elongated ribbon portions (16) spaced by intervening elongated gaps (17). An electro-expulsive device (10) according to claim 5, characterized in that said first (34) and second (36) connector means are spaced along said ribbon portions (16) and disposed in said intervening gaps (17). An electro-expulsive device (10) according to any of the preceding claims, characterized in that said first (34) and second (36) connector means have an elastic memory thereby providing a restoring force tending to return said conductor means to the rest position when de-energized. An electro-expulsive device (10) according to any of the preceding claims characterized in that the electric current supplied to the conductor means (13, 14) has such a shape that a force of sufficient magnitude is generated to expulse solid or frangible material bonded to the surface of the electro-expulsive device during a time interval of 10 to 80 microseconds.

Inventors: GOLDBERG JOSHUA I, LARDIERE BENJAMIN G JR, GOLDBERG, JOSHUA I., LARDIERE, BENJAMIN G. JR.
Applicants: DATAPRODUCTS NEW ENGLAND INC, DATAPRODUCTS NEW ENGLAND, INCORPORATED
Application year: 1990
Main classification: B64D15
IPC codes: B64D15