AU2003200330B2 - Flat spring drive system and window cover - Google Patents

Description

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant: Actual Inventors: Address for Service: Invention Title: Andrew J. Toti TOTI, Andrew, J.

DAVIES COLLISON CAVE, Patent Attorneys, 1 Little Collins Street, Melbourne, 3000 Flat spring drive system and window cover The following statement is a full description of this invention, including the best method of performing it known to us.

QAOPER\ArUanU290694 23.doc 30/1/03 P: %OPERI.SH2608979-2sa do-703/2007f t-1- SFLAT SPRING DRIVE SYSTEM AND WINDOW COVER The present invention relates generally to flat spring drives or motors, which are useful in numerous applications and, in particular, relates to the Cc application of such flat spring drives in window cover systems.

Typically, as used here, "cover" refer to expandable or extendible structures. These include slat structures such as so-called Venetian or slat blinds and socalled mini-blinds. These structures also include pleated folding structures such as single and plural pleat structures and box, hollow and cellular structures. "Cover" also refers to flat, sheet-type covers such as roller blinds. In this document, "cover" and "blind" are frequently used interchangeably. As applied to such covers, "operate" refers to the process of closing and opening the covers, typically (for horizontal covers) to lowering and raising the cover.

As used here, "horizontal" window cover refers to horizontally oriented covers such as horizontal slat blinds, horizontal folded pleat blinds and horizontal cellular blinds. The present invention is applicable generally to horizontal window cover systems and to flat window cover systems. It is understood that "window," as used for example in "window cover," includes windows, doorways, openings in general and even non-opening areas or regions to which covers are applied for decoration, display, etc.

As used here, the terms "operatively connected," "operatively coupled," "operatively connected or coupled" and the like include both direct connections of one component to another without intervening components and connections via intervening components including gears, transmissions, etc.

Typically a horizontal cover or blind is mounted above the window or space which is to be covered, and is operated using lift cords to extend the cover and lower it across the area, stopping at a selected position at which the blind partially or fully covers the area. For most horizontal slat blinds, the lift cords are attached to a bottom rail and the "rungs" or cross-members of a separate cord ladder are positioned beneath the slats of the blind. When the blind is fully lowered, each slat is supported by a rung of the blind's cord ladder and relatively little weight is supported by the lift cords. However, as the blind is raised, the slats are "collected" on the bottom rail, and the support of the slats is thus increasingly transferred from the cord ladder to the bottom rail and the weight supported by the rail and the lift cords increases.

Many pleated, cellular, box, etc., blinds are formed of resilient material having inherent spring-like characteristics. As the resilient pleated blind is raised toward the fully open position, the blind material is increasingly compressed, and requires increasingly greater force to overcome the compression force and move the blind and hold the blind in position. Effectively, then, both the slat blind and the pleated blind require increasingly greater force to open the blind and to maintain the blind open than is required to close the blind and maintain the blind closed.

The operating characteristics of conventional constant torque flat spring drives, especially long blinds, make it difficult to assist the opening and P \OPERRSH608979-2sap d~c-.7f)3/2(X)7 -3closing operation of horizontal and flat blinds. As applied to downward-closing embodiments of such blinds, spring drives usually are mounted at the top of the blind, and are operatively connected or coupled to the shaft about which the blind lift cords are wound. As described above, as the blind is lowered, the slat weight supported by the lift cords decreases and the compression of the pleats decreases. However, the torque force of the spring remains relatively constant, with the result that the spring torque may overcome the decreasing supported weight or the decreasing compression force, and raise the blind in fast, uncontrolled fashion. Also, it may be difficult to keep the blind at a selected position.

Furthermore, if the blind is heavy, and requires a strong spring to maintain the blind open, the blind is particularly susceptible to instability and uncontrolled raising operation when partially or fully closed.

One aspect of the present invention provides a window cover system, comprising: an extendible window cover; a housing; lift cords attached to the cover and wrapped around rotatable pulleys mounted to the housing for raising and lowering the extendible cover; and a spring drive system connected to the lift cords for assisting the raising and lowering of the cover, the spring drive system comprising a flat spring drive mounted to the housing and having a first rotatable end and a second rotatable end; and a gear transmission of fixed ratio, the gear transmission operatively connected at one end via a bevel gear set to the second rotatable spring end and at the opposite end to the rotatable lift cord pulleys for rotating and being rotated by the lift cord pulleys, the gear transmission thereby applying the fixed ratio thereof between the flat spring drive and the lift cord pulleys, thereby controlling a force applied to the extendible cover by the flat spring drive.

P:\OPER\RSH\26 9979.2spa do-73/3fl )7 -3A- SA further aspect of the present invention provides a window cover system, C comprising: an extendible window cover; a housing; lift cords attached to the cover and wrapped around pulleys mounted to the housing for raising and lowering the extendible cover; and a spring drive system operatively connected to the lift cords for assisting the S 5 raising and lowering of the extendible cover, the spring drive system comprising a flat spring drive mounted to the housing and having a first rotatable end and a second rotatable Cc end; and a bevel gear set having one gear operatively connected to the second rotatable spring end and a second gear operatively connected to the lift cord pulleys for rotating and being rotated by the lift cord pulleys.

Preferably, the flat spring drive has a torque or force which decreases as the extendible cover is lowered and increases as the extendible cover is raised, the flat spring drive applying the variable torque or force to the extendible cover.

A further aspect of the present invention provides a window cover system comprising: a base; an extendible window cover; and lift cords attached to the extendible cover and wrapped around pulleys mounted to the base for lowering and raising the extendible cover; and a spring drive system connected to the lift cords for assisting the lowering and raising of the extendible cover, the spring drive system comprising: a flat spring drive mounted to the base and having a first rotatable end and a second rotatable end, the second rotatable end applying a torque or force for assisting the lowering and raising of the extendible cover; and a variable transmission comprising a band or cord rotatably wrapped around two drums, a first of the drums being operatively connected to the second rotatable end of the flat spring drive for rotation therewith and the second drum being operatively connected to the lift cord pulleys for rotation therewith, the variable transmission having a ratio which varies as the drums thereof wind and unwind, thereby causing the lift cord pulleys to rotate at a rate that varies relative to the rate of the second rotatable end of the spring and varies the overall spring drive-to-pulley ratio.

Another aspect of the present invention provides a window cover system, comprising: a base; an extendible window cover; and lift means including a rotatable shaft P NOPERMSH2608979-2spa doM.73/2007 -3B mounted to the base, a plurality of pulleys mounted on the shaft for rotation therewith, and a plurality of lift cords wound around the pulleys and attached to the extendible cover for raising and lowering the extendible cover to selected positions; a spring drive unit operatively connected to the lift means for assisting the raising and lowering of the extendible cover to selected positions, the spring drive unit comprising a spring drive mounted to the base and having a first rotatable end and a second rotatable end; and a gear transmission of fixed ratio; the gear transmission operatively connected between the second rotatable end of the spring drive and the lift means, thereby applying the fixed ratio of the gear transmission between the second rotatable end of the spring drive and the lift means, for altering the force applied between the spring drive and the extendible cover.

In one embodiment, the present invention is embodied in a spring drive which comprises a storage drum, an output drum, and a flat spring wound on the two drums. In a preferred embodiment, the flat spring is adapted for providing a torque which varies along the length of the spring. In one specific aspect, the spring has a cove of selected curvature Application No: 2003 200330 Pages 3C to 3E have been deleted by amendment item 3.

P:\OPERAlI\2608979pcc page.do-29/01/03 3F which varies along the length of the spring for providing torque which varies proportional to the cove as the spring winds and unwinds. In another specific aspect, the spring has holes of selected size and location along the spring axis for providing torque which varies indirectly proportional to the transverse size of the holes and the resulting effective width of the spring as the spring winds and unwinds.

In another embodiment, the present invention is embodied in a plural spring drive system comprising an output drum; and a plurality of storage drums, each having a flat spring wound thereon. The plurality of flat springs extend to and are wound together in overlapping fashion on the output drum, such that the system torque at the output drum is a multiple of the torques associated with the individual flat springs. Various alternative arrangements can be used, for example, the storage drums can be arranged in approximately a straight line; the output drum and the storage drums can be arranged in approximately a straight line; the storage drums can be arranged in a cluster; and the output drum and the storage drums can be arranged in a cluster. In a preferred embodiment, at least one of the flat springs is adapted for imparting a torque component to the system torque which varies along the length of the said one spring. In one specific embodiment, the said one spring has a cove or transverse curvature which selectively varies along the length of the said spring for providing torque which varies proportional to the transverse curvature of the said spring at a position closely adjacent the output drum as the said spring winds and unwinds. In another specific embodiment, the said one spring has holes along its length for providing torque which varies proportional to the transverse size of the holes and the resulting effective width of the said spring when one or more holes is positioned closely adjacent the output drum as the spring winds and unwinds.

In another embodiment, the spring drive further comprises a magnetic brake comprising one or more magnetizable regions or magnets at selected positions along the flat spring, or at least one of the flat springs; and a magnet brake member mounted adjacent the flat spring, so the brake member stops the flat spring at the selected positions.

In yet another embodiment, the spring drive further comprises a detent brake comprising one or more holes at selected positions along the flat spring, or at least one of the flat springs; and a detent brake member biased against the flat spring for engaging the holes and stopping the flat spring at the selected positions.

In specific applications embodying the present invention, one or more of the spring drives are incorporated in window cover systems for providing torque or force tailored to the operating characteristics of the cover. In another application, the spring drive (or drives) is used in combination with one or more band shift transmissions for varying the drive force of the spring; one or more gear transmissions for providing a fixed gear ratio to fixedly alter the drive force of the spring; and one or more connecting gear sets and mechanisms. In addition to controlling the applied force of the spring, the transmissions alter the length of the I I i' i cover and provide inertia and friction for maintaining the blind at selected positions between and including open and closed positions.

Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, as set out below.

FIG. 1 is a front elevation view of a horizontal slat blind window cover system, showing the cover in a lowered (closed) condition.

FIG. 2 is a front elevation view of the window cover system of FIG.

1, showing the cover in a near fully-raised (near open) condition.

FIG. 3 is a front elevation view of a horizontal pleated blind window cover system, showing the cover in a lowered (closed) condition.

FIG. 4 is a front elevation view of the window cover system of FIG.

3, showing the cover in a near fully-raised (near open) condition.

FIG. 5 is a perspective of a band shift transmission 4n-.accordance with a preferred embodiment of the present invention.

FIG. 6 is a perspective of a flat spring drive.

FIG. 7 is a perspective of a varied torque, flat spring drive having varied cove in accordance with a preferred embodiment of the present invention.

FIG. 8 is a perspective of a varied torque, flat spring drive having holes in accordance with a preferred embodiment of the present invention.

P I FIG. 9 is a perspective view of the band of FIG. FIG. 10 is a perspective view of the flat spring of FIG. 6.

FIG. 11 is a perspective view of the varied cove spring of FIG. 7.

FIG. 12 is a perspective view of the perforated spring of FIG. 8.

FIGS. 13-19 are top plan views of spring drive units according to embodiments of the present invention.

FIGS. 20-28 and 42 depict additional embodiments of the perforated spring of FIG. 12.

FIGS. 29 and 30 are top and side views, respectively, of a perforated spring comprising separate sections joining by various joining means or members.

FIGS. 31 and 32 are top and side views, respectively, of a nonperforated sectioned spring.

FIGS. 33-37 depict magnetic and detent brakes and components useful in spring drives.

FIG. 38 depicts a single spring drive unit which includes three lift cords and pulleys.

FIG. 39 depicts a window cover which includes a pair of drive units, each of which is similar to that of FIG. 38, but includes two pulleys and associated lift cords.

FIG. 40 depicts a window cover comprising a pair of spring drive units similar to those of FIG. 38 without the power transfer bar and with only one pulley in each drive unit.

SI 1 I FIG. 41 depicts representative examples of the lift cord paths for two and four cord systems.

FIG. 43 is a perspective view of a varied torque, torque-multiplying, S plural flat spring drive in accordance with a preferred embodiment of the present invention.

FIG. 44 is a simplified front elevation depiction of FIG. 43 illustrating the relationship of the two spring drives and their overlapping springs.

FIG. 45 is a top plan view of a spring drive unit embodying the plural spring drives of FIG. 43.

1. Examples of Applicable Blinds FIGS. 1 and 2 depict a conventional horizontal slat (venetian) window cover system 10 in closed (fully lowered) and nearly fully open positions, respectively. The cover system 10 comprises an elongated top housing or support 11 within which a spring drive unit such as unit 15. FIG. 13, is mounted. The associated blind 12 comprises horizontal slats 13 and a bottom rail 14 which can be the same as the slats but, preferably, is weighted to enhance the stability of the blind 12.

FIGS. 3 and 4 depict a conventional horizontal pleated blind cover system 20 in closed and nearly fully open positions, respectively. The blind cover system 20 comprises housing 11 within which the spring drive unit 15 is mounted.

The associated blind 22 typically comprises light weight fabric or other material which is resilient and maintains the shape of horizontal pleats 23. The blind also includes a bottom rail 24 which is sufficiently heavy, or weighted, to provide stability to the blind 22.

Regarding slat blind 10, FIGS. 1 and 2, and as is typical of such blinds, spaced cord ladders 17 are suspended from the support 11 and the rungs 21 of the ladders are routed along and/or attached the underside of the individual slats 13 so that when the ladders are fully extended (lowered) and the blind 12 is thus fully lowered, as depicted in FIG. 1, the weight of each slat is supported by the ladders, with little weight on the lift cords. In contrast, as the blind 12 is raised from the lowermost position, for example to the partially raised/lowered position depicted in FIG. 2, the slats are sequentially "collected" on the bottom rail 14, starting with the bottommost slats, so that an increasing weight is supported on the bottom rail and by the lift cords 16. Thus, and perhaps counter-intuitively, the weight supported by the lift cords is a maximum when the blind is fully open (raised), and a minimum when the blind is fully closed (lowered).

As discussed previously, the force requirements of horizontal pleated blinds such as blind 20, FIGS. 3 and 4 are somewhat similar to the slat blind 10 in that the compression of the pleats 23 increasingly opposes movement of the blind as it is raised, thus increasing the force required to open the blind and to maintain the blind in position. Conversely, the decreasing compression of the material as the blind is lowered toward the closed position decreases the force requirement.

The following exemplary spring drives and transmissions are used in any combination to provide easy-to-use, stable window covering operation. Section 2 below contains a brief discussion of the spring drives shown in FIGS. 5-12 and two transmissions. In section 3, the various combinations depicted in FIGS. 13-19 are discussed.

2. SDrin Drives and Transmissions.

a. Band Shift Transmission FIGS. 5 and 9 depict a band shift transmission or gear unit 21 which comprises a pair of drums or spools 22, 23, about which is wound a cord or band 24. Preferably the band is an elongated strip of thin cloth or thin steel having a flat rectangular cross-section. However, other suitable materials can be used, and other cross-section shapes can be used which provide controlled variation in the radii on the drums. For example, a circular or oval cross-section cord-type band can be used. As used here, the term "band" includes, in accordance with the preferred embodiment, a thin, flat rectangular shape, but also includes other suitable crosssection shapes as well.

The band shift transmission (also, simply "band transmission" or "shift transmission") provides a varying drive ratio which is used to increase or diminish the torque or force of the spring drive unit. The band shift transmission applies the varying drive ratio between the spring drive and the lift cord pulleys.

The ratio of the band transmission is determined by the radius of the band stored on each drum. The radii vary as the band winds and unwinds, varying the associated gear ratio. Thus, increasing (decreasing) the thickness of the band, increases the rate at which the radii increase and decrease, and increases the gear ratio provided by the transmission. By way of example but not limitation, a band thickness of 0.014 inches has given satisfactory results.

The manner of mounting the band can be used to decrease or increase the ratio of the speed of the spring output drum relative to that of the lift cord pulleys as the blind is lowered. Preferably, the band 24 is mounted so the band radius on output drum 23 increases relative to the band radius on storage drum 22 as the blind is lowered, and decreases as the blind is raised, thus offsetting or decreasing the power with which the spring would otherwise oppose the blind, enhancing or increasing somewhat the lifting power of the spring during raising of the blind, increasing the distance traveled by the blind relative to the spring drive, and increasing the maximum operational length of the blind (the distance between the fully raised and fully lowered positions). Of course, the band shift transmission 21 can be arranged so the output drum radius decreases relative to the storage drum radius as the blind is lowered and increases relative to the storage drum radius as the blind is raised, thereby increasing the force during lowering of the blind, decreasing the force during raising of the blind and decreasing blind length.

b. Flat Spring Drives Referring now to FIGS. 6 and 10, conventional "flat" spring drive unit 26 comprises a pair of drums or spools 27, 28, about which is wound a flat metal spring 29 that provides nearly constant torque regardless of its wound position on the drums.

Referring next to FIGS. 7 and 11, varied torque flat spring drive unit 31 comprises a flat metal spring 34 of varying cove, which is wound around drums "or spools 32, 33. One drum, such as left drum 32 is a storage drum; the other drum 33 is the output drum. The torque or force of the spring 34 is directly proportional to the degree of cove or transverse curvature of the spring. Thus, for example, and in one preferred embodiment, the cove varies from a relatively small degree of transverse curvature (nearly flat, small cove) at end 36 to a relatively large degree of curvature (large cove) at the opposite end 37. Examples, representative, but by no means limiting, are 3/8 W x 1/16 R of curvature or "coveness" at the shallow coved end and 3/8W x 3/8R of coveness at the highly coved end (W and R are, respectively, width and radius in inches.).

Referring next to FIGS. 8 and 12, varied torque flat spring drive 41 comprises a perforated spring 44 which is wound around wheels or spools 32, 33.

Again drum 32 is the storage drum and drum 33 is the output drum. The torque or force of the spring 44 is directly proportional to the amount of spring material at a given point or region. The number, location, size and/or shape of the perforations or holes can be tailored to provide many different force curves, including constantly varying (decreasing or increasing), intermittent or discrete variations such as sawtooth or spiked force patterns, cyclical or sinusoidal patterns, etc. Thus, for example, and in one preferred embodiment, a line of spaced holes is formed generally along the center line of the spring 44, increasing in diameter from holes 47 of relatively small diameter near end 46 to relatively large diameter holes 48 near opposite end 49. As a result, the torque or force effected by the spring 44 decreases from a relatively large magnitude at end 46 to a relatively small magnitude at end 49. The hole size and spacing is selected to provide a drive force which varies in direct proportion to the lift cord-supported weight or the compression of the blind 12, 22. That is, the force decreases as the spring is unwound toward the blind-fully-down position shown in FIGS. 1 and 3 and, conversely, increases as the spring is wound or rewound as shown in FIGS. 2 and 4 toward the blind-fully-up position. (This is in direct contrast to the operation of coil springs, whose spring force varies inversely to the variation of the cordsupported weight of the blind, and constant torque flat springs, whose force is approximately constant as the spring unwinds and winds.) In general, the spring drive units 31 and 41 are configured so that contrary to the usual coil spring or flat spring operating characteristics, as the spring unwinds or winds as the blind is lowered or raised, the spring torque or force decreases or increases in direct proportion to, and remains closely matched to, the supported weight or compressive force of the blind; from a fully or partially open position, the blind is easily lowered to any selected position by a slight downward pull on the blind; from a fully or partially closed position, a slight upward push by hand is sufficient to raise the blind to any selected position; and (4) the stability of the blind is enhanced in that the tendency of the blind to move from the selected positions is suppressed.

c. Transmission The spring drive unit such as 26, 31, 41 is operatively connected by bevel gear set 60 to shaft 50, FIG. 13, and transmission 70. As described in detail below, the shaft 50 is connected to transmission idler gear 71, so that the right side, output drum rotates with the idler gear 71 of the transmission 70 and vice versa.

The transmission 70 is designed to either offset or supplement the operating characteristics of the spring drive unit, as desired.

In one illustrated exemplary embodiment, the transmission comprises an array of gears 71, 73, 75 and 77, in which idler gears 71 and 73 are intermeshed and idler gear 75 and power gear 77 are intermeshed. Idler gear 71 and an integral sleeve or collar are mounted on and rotate with shaft section 53 and vice versa. Gears 73 and 75 are joined, forming a gear set. This gear set and an integral collar are mounted on and fastened to shaft 74, which is mounted to and between supports 84 and 86. Power gear 77 and an integral collar are mounted on and fastened to shaft section 53. Power gear 77 meshes with gear 75 of the two-gear set, the other gear 73 of which meshes with idler gear 71.

As mentioned, shaft end section 53 is part of the interconnected shafts (or shaft sections). Thus, at one end of the transmission gear train, power gear 77 is joined to and rotates at the same rate as the shaft 53 and lift cord pulleys 19-19.

At the opposite end of the transmission gear train, idler gear 71 and interconnected bevel gear 62 rotate freely about the shaft 50 and are connected via bevel gear 61 to the right side drum of the spring drive. As the result of this arrangement, the pulleys 19-19 and the lift cords 16, 17 rotate at one rate, the same rate as gear 77 and shaft 50, and the spring rotates at another rate, the same rate at which the right side output drum, the idler gear 71 and the bevel gears Preferably the transmission gear ratio is selected so that the idler gear 71 and spring drive 26, 31, 41 rotate at a slower rate than the power gear 77 and the lift cords 16, 17. For example in one application, the fixed drive ratio of the transmission 70 is 1:3 to 1:8 so that gear 77 and pulleys 19-19 rotate 3-8 revolutions for each revolution of the right side output drum. Obviously, however, in applications where such is advantageous, the drive ratio of the transmission can be selected to rotate the spring drive faster than the pulleys.

The above transmission gear ratios and the different rotation rates diminish proportionately the torque exerted by the spring 29, 34, 44 as it is wound in one direction and the blind is lowered. This permits the use of a powerful spring to hold a large, heavy blind in position at the uppermost position, where the supported weight and the pleat compression is the greatest, and diminishes the force otherwise exerted by the spring at the lowermost, closed condition where the supported weight and the pleat compression is a minimum. As a result, a powerful spring does not overpower the weight of the blind and does not uncontrollably raise the blind. The transmission gear ratio also increases the length of travel available to the blind for a given spring, permitting a longer blind for a given spring or a given spring travel. Furthermore, the transmission 70 has inherent friction which acts as a brake and retains the blind at selected positions between and including fully open and fully closed. The combination of the preferably v arying torque/force provided by the flat spring drive directly proportional to the supported weight/compression of the blind;, the transmission gear ratio; and the gear friction allows the spring drive unit to hold the blind 10, 20 in. position at even the "heaviest" (uppermost) blind positions, and allows the blind to be pulled downward to any selected position by gently pulling the blind to that position and, conversely, to be pushed upward to any selected position by gently pushing- upward to that position. Little force is required to move the blind up and down, the blind stops accurately at any selected position between and including the fully open and fully blosed positions, and the blind remains at the selected. positions.

3. Flat Sring2 Drive Window Covers a. SrnDrvanTanission FjG. 131 Referring further to FIG. 13, there is shown spring drive unit 15 according to an embodiment of the present invention. The spring drive unit is mounted inside.

housing I11 and includes shaft 50 comprising left shaft or section 51 and right shaft or section 52. Adjacent ends 53, 54 of the shafts 51, 52 have reduced radius or size and are joined by collar 56. The separate shaft sections facilitate the removal of shaft 50 and the installation and replacement of the drive components mounted on the shaft. The shaft 50 is rotatably jou-naled within transverse walls or support members 57, 58. Two lift cord pulleys 19 and 19 are mounted on the shaft adjacent the transverse walls 57 and 58. The spaced lift cords 16 and 17 are attached to bottom rail 14 (FIG. 24 (FIG. 3) and are wound about the pulleys 19-19 for raising and lowering the bottom rail and thus the blind 10 or Referring. further to FIG. 13, flat spring drive 26, 31 or 41 is mounted on transverse shafts 81, 82. The outer end of each shaft is mounted to the housing 11 and the opposite, inner end is mounted to longitudinal wall or support member 83. Of these spring drives, unit 26 is a conventional constant force or torque drive. However, spring drives 31 and 41 are unique variable force or torque units in .accordance with the present invention, which preferably are specially adapted to provide a drive force which varies in direct proportion to the lift cordsupported blind weight or the pleat compressive force. That is, the spring force changes, preferably decreases, as the spring is unwound and the blind is extended toward the fully-down position and, conversely, increases as the spring is wound and the blind is retracted toward the fully-up position. (This is in direct contrast to the operation of coil springs, in which the spring force varies inversely to the variation of the cord-supported weight or compression of the blind.) The output of the spring drive 26, 31, 41 is connected via power "transfer bevel gear set 60 and transmission 70 to the cord pulleys 19-19. One gear 61 of bevel gear set 60 is mounted on drum mounting shaft 82 and meshes with the second gear 62, which is mounted on section 53 of shaft 50. The second bevel gear 62 is connected to the transmission 70, which is mounted on shaft section 53. The transmission varies the rate at which the cord pulleys 19 and 19 rotate relative to the rotating drum of the spring drive.

Illustratively, in one application, the transmission gear ratio is 3:1 to 8:1 so that lift cord pulleys 19-19 rotate 3-8 revolutions for each revolution of the rotating spring drive spool.

As alluded to, preferably, a varied force spring drive unit is used, one which exerts diminished force as the blind is lowered, and preferably one which tracks the decreasing supported weight or compression force of the blind 10, 20 as the blind is lowered. The above transmission gear ratios and the different pulley and spring rotation rates diminish proportionately the force exerted by the spring as it is wound and the blind is lowered. This permits the use of a more powerful spring to hold a large, heavy blind in position at the uppermost position, where the cordsupported weight is the greatest, and proportionately diminishes the force exerted by the spring at the lowermost, closed condition when the supported weight is a minimum, so that the powerful spring does not overpower the weight of the blind and does not uncontrollably raise the blind. The gear ratio also increases the length of travel available to the blind for a given spring, permitting a longer blind for a given spring or a given spring travel. (For example, for the described 3:1 ratio, the possible blind length is 3 times the maximum spring rotation.) Furthermore, the transmission 70 and the bevel gear set 60 have inherent friction which individually and collectively act as a brake and retain the blind at any selected position between and including fully open and fully closed. The combination of the preferably varied force spring drive, the transmission gear ratio and the gear friction allow the spring to hold the blind in position at even the "heaviest" (uppermost) blind positions, and allow the blind to be pulled downward to any selected position by gently pulling the blind to that position and, conversely, to be pushed upward to any §elected position by gently pushing upward to that position. Little force is required to move the blind up and down, the blind stops accurately at any selected position between and including the fully open and fully closed positions, and the blind remains at the selected positions.

b. Spring Drive and Bevel Gears (FIG. 14) FIG. 14 depicts a spring drive unit 15A which is essentially unit FIG. 13 without the transmission 70. Also, the shaft 50 depicted in the figure is of one-piece construction. A constant or varied force spring drive 26' 31, 41 is mounted on the transverse shafts 81 and 82, with shaft 82 also mounting bevel gear 61. Mating bevel gear 62 is mounted on the shaft 50 and, as a result, the shaft 82 and associated rotating spring drum are connected by the bevel gear set 60 directly to shaft 50 and the lift cord pulleys 19-19, and rotate at the same rate as the pulleys.

Although a constant force spring drive can be used, a varied force drive is much preferred, to tailor the spring force to the blind weight or compression, as described above relative to FIG. 13. In addition, the bevel gear set 60 provides friction which assists the constant or the varied force spring drive in maintaining the blind at the selected positions. The bevel gear set 60 can be a 1:1 direct drive or a non-direct drive.

c. Sprin g Drive and Transfer Gears (FIG. FIG. 15 depicts a spring drive unit 15B which is yet another alternative to the drive unit 15, FIG. 13. A constant or a varied force spring drive 26, 31, 41 is mounted on shafts 81, 82, which extend the entire width of the housing 11 and are supported by the longitudinal (front and rear) housing walls.

Cord pulley set 18 comprises two pulleys 19-19 mounted adjacent the spring drive unit on shaft 88. The spring drive unit is directly connected to the cord pulley unit 18 by a power transfer spur gear set 65 comprising gear 66 which is mounted on spring drive drum shaft 82 and meshes with gear 67, which is mounted on cord pulley shaft 88. When a constant force spring drive is used, obviously the spring force does not track the blind weight or compression. However, the power transfer gear set permits tailoring the spring drive unit to the blind operation in that the gear set 65 can be a 1:1 direct drive so that the unit transmits power directly with only frictional loss, or can have a selected non-direct gear ratio for varying the spring force as described above, and thus assisting in tailoring the spring force to the varying blind weight or compression, and has inherent friction which assists retaining the blind at the selected positions. When a varied force spring drive unit is used, preferably the varied force is tailored to the variation in the supported weight of the blind, the power transfer gear set friction assists in retaining the blind at the selected positions, and the power transfer gear set may be direct drive or have a gear ratio which assists in tailoring the spring force to the varied supported weight or compression characteristics of the blind.

d. Sprin2 Drive and Transfer Gears (FIG. 16) FIG. 16 depicts an alternative embodiment 15C to the spring drive unit 15B, FIG. 15. The compact unit 15C comprises the spring drive 26, 31, 41; the cord pulley unit, and power transfer spur gear set 65. The difference is that the housing 11 contains four shafts 81, 82, 91 and 92, and the power transfer gear set 65 comprises three gears 66, 67, 68. Gear 66 is mounted on shaft 82 as in FIG. and gear 67 is mounted on shaft 92 with pulley set 18. However, middle gear 68 is mounted on shaft 91. The three gear unit 65 operates differently from the two gear unit in that it is a power transfer and/or ratio unit. Otherwise, the unit operates the same as unit 15B, FIG. 15, and the components function as described above with regard to unit e. Spring Drive. Band Shift Transmission and Transfer Gears FIG. 17) FIG. 17 depicts a compact spring drive unit 15SD which is yet another alternative to the drive unit 15, FIG. 13. The housing 11 contains transverse shafts S 81, 82, 91 and 92. Spring drive 26, 31 or 41 is mounted on shafts 81 and 82 and is connected to cord pulley unit 18 by a power transfer gear unit 65 and a band shift transmission or gear unit 21. The power transfer gear unit 65 comprises gear 66 which is mounted on drum shaft 82 and meshes with gear 67, which is mounted on shaft 91. One drum 22 of the band shift transmission 21 is also mounted on the shaft 91 and the second drum 23 is mounted on shaft 92 along with the cord pulley unit 18, which comprises two cord pulleys 19-19 for the lift cords 16 and 17.

When a constant force flat spring drive 26 is used, the unit 15D has several features which improve the operation of the blind despite the limitation of constant spring drive force: the band shift transmission 21 varies the spring force, preferably directly proportional to the varying weight or compression of the blind, the power transfer gear unit 65 may be direct drive or may have a selected gear ratio for additionally varying the spring force as described above, and the power transfer gear unit also provides friction which assists in retaining the blind at the selected positions. Alternatively, when a varied force flat spring drive unit is used, the varied force of the spring drive preferably is directly proportional to the varying weight or compression of the blind, the band transmission provides additional variation of the spring force, preferably directly proportional to the weight or compression of the blind, the power transfer gear unit may be direct drive or may have a selected gear ratio for additionally varying the spring force and the power transfer gear unit also provides friction which assists retaining the blind at the selected positions: f. Sarin Drive Transmission and Transfer Gears (FIG. 18) FIG. 18 depicts a compact spring drive unit 15E which is another embodiment of the present invention. The unit 15E comprises a flat spring drive 26, 31 or.41 which is operatively connected to a two-gear power transfer unit 65, which in turn transmits force via transmission 70 to the pulley unit 18, and vice versa.

Specifically, the spring drive is mounted on transverse shafts 81, 82; one gear 66 of the set 65 is mounted on the shaft 82 with the associated drum and meshes with the gear 67, which is mounted on shaft 92. Transmission 70 is also mounted on the shaft 92 in the manner described relative to the mounting on shaft 50, FIG. 13, along with the pulley unit 18. As a result, the power transfer gear-unit 65 and the transmission 70 transfer force from the spring drive to the pulley unit, and vice versa.

Preferably, a varied force spring drive unit is used, one which exerts diminished force as the blind is lowered, and preferably one which tracks the decreasing supported weight or compression force of the blind 10, 20 as the blind is lowered. The above transmission gear ratios and the different pulley and spring rotation rates diminish proportionately the force exerted by the spring as it is wound and the blind is lowered. The gear ratio also increases the length of travel available to the blind for a given spring, permitting a longer blind for a given spring or a given spring travel. As discussed previously, the power transfer gear unit may be direct drive or may have a selected gear ratio for additionally varying the spring force. Furthermore, the transmission and the power transfer gear set have inherent friction which individually and collectively act as a brake and retain the blind at any selected position between and including fully open and fully closed.

g. Sprin Drive, Transmission Band Shift Transmission and Transfer Gears (IG. 19) FIG. 19 depicts an embodiment 15F of the spring drive unit which includes a chain drive for the purpose of transferring power and/or ratio.

Illustratively, spring drive 26, 31 or 41 is mounted on shafts 81 and 82; band shift transmission 21 is mounted on shafts 82 and 91; chain drive 94 is mounted on shafts 91 and 92; two pulley units 18, 18 are mounted on shaft 92 for the purpose of powering the cord pulleys; and transmission 70 is mounted on shaft 91 between unit 21 and chain drive 94. The unit 15F features the combination of varied drive force from the spring drive, varied gear ratio from unit 21, constant gear ratio from transmission 70, and frictional holding force from transmission h. Additional Perforated Spring Embodiments (FIGS. 20-32) FIGS. 20-32 depict several of the many possible additional embodiments of the perforated spring 44, FIGS. 8 and 12.

In FIG. 20, spring 44A comprises an array of elongated slots of generally uniform size positioned along the longitudinal center axis of the spring.

The spring 44B of FIG. 21 comprises a similar array of uniform elongated slots, flanked by a line of alternating holes along each outside edges of the spring, with the holes in each line being spaced one hole per two slots..

The spring 44C of FIG. 22 has a similar array of uniform elongated slots, flanked by two lines of holes along the outside edges of the spring, with a hole at each end of the individual slots.

FIG. 23 depicts a spring 44D comprising an array of elongated slots of increasing length positioned along the longitudinal center axis of the spring.

In FIG. 24, spring 44E comprises an array of generally circular holes of the same size positioned along the longitudinal center axis of the spring.

The spring 44F of FIG. 25 comprises an array of generally circular, like-sized holes positioned along the longitudinal center axis of the spring, flanked by lines of alternating holes along the outside edges of the spring, with the holes in each line spaced one hole per two slots.

The spring 44G of FIG. 26 comprises an array of generally circular holes of uniform size positioned along the longitudinal center axis of the spring, flanked by a line of alternating holes along each outside edge of the spring, with the holes in each line being spaced one hole per slot.

In FIG. 27, spring 44H comprises five longitudinal lines of generally circular holes of like size, with the holes of adjacent lines positioned at alternating positions along the spring.

FIG. 28 depicts a spring 441 comprising an array of generally circular holes of increasing radii positioned along the longitudinal center axis of the spring.

In FIGS. 20-22 and 24-26, one end of the spring does not have slots, so that the spring torque or force maintains a relatively constant maximum along the "slot-free end.

FIGS. 29 and 30 depict a perforated spring 44K illustratively comprising three sections 112, 113 and 114 which are joined by a tongue-in-groove arrangement 116 (sections 112 and 113) and rivet 117 (sections 113 and 114). The spring torque is controlled by the different cross-sectional dimensions of the sections as well as the size and spacing of the perforations.

FIGS. 31 and 32 depict an alternative, non-perforated sectioned spring 44L, illustratively comprising three sections 118, 119 and 121 which are joined by' rivets 122 (sections 118 and 119) and a link 123 (sections 119 and 121). The spring torque is controlled by the cross-sectional dimensions of the sections.

FIG. 42 depicts yet another alternative perforated spring 44M which, illustratively, comprises two laterally spaced parallel rows of longitudinally spaced, longitudinally elongated slots 42. The length of the slots and the spacing between the slots are selected to vary the torque output of the spring along the length of the spring. Slots are preferred to holes because the elongation of the slots has a more uniform cross-section along the width of the spring than circular holes and thus more uniform torque along the length of the slots.

i, Magnetic and Detent Brake Embodiments (FIGS. 33-37) FIGS. 33-37 illustrate the use of magnetic and detent brakes in spring drives. FIG. 33 depicts a spring drive which incorporates two brake devices, a magnet brake 100 and a detent brake 105. Both devices are shown in one figure, although either one or both devices can be used. Regarding magnet brake 100and referring also to FIGS. 34-37, the spring contains thin magnetic or magnetized sections 95 which in the illustrated embodiment extend transverse (side-to-side) on the spring. Preferably, several of the sections are placed closely adjacent one another at locations of the spring where it is desired to stop the spring, for example at spring positions corresponding to blind fully open and fully closed positions and intermediate positions, including a large number of closely spaced intermediate stop positions. For example, FIG. 34 depicts a varied-cove spring embodiment 34A having magnet strip 95-defined stop positions at a multiplicity of positions. FIG. depicts an embodiment 34B having magnet strip 95-defined stop positions proximate the ends of the spring. FIGS. 36 and 37 illustrate springs 34C and 44J, respectively, having magnet strip 95-defined stop positions at one end of the spring.

Referring now to FIG. 33, the exemplary magnet brake 100 comprises a magnet bar 101 mounted for pivotal movement by pin or shaft 102 which is mounted to the housing 11. Spring 103 is mounted to bar or rod 104 extending from the housing and biases the magnet bar lightly closely adjacent the outside surface of spring such as spring 34A, 34B, 34C and 44J wound on associated drum such as 28. The magnet bar 101 rides lightly along or in close proximity to the spring with no effect on the operation of the spring drive until the bar reaches the magnet sections 95, which are attracted to the bar. Preferably, the magnetic force is sufficient to maintain the spring drive and blind at the given position when the blind is brought to rest at that position, and is sufficient to stop a very slowly moving blind at that position (that is, to stop the blind as a person slows movement of the blind to stop it proximate the position of the magnet strips), but is insufficient to stop the blind as it is raised and lowered at a normal speed.

The detent brake 105 shown in FIG. 33 comprises a bar 106 extending in a transverse direction from the housing 11 adjacent the spring between the associated drums, a detent 107 mounted on a pin 108 projecting downward through a hole in the bar 106, and a spring 109 between the bar 106 and the detent 107 for biasing the detent lightly against the spring. As shown in FIG. 36, the spring 34C may comprise one or a plurality of holes 96 which accept the detent I 1 107. Alternatively, referring to FIG. 37, holes at selected positions in the perforation-derived varied force spring may be of suitable size to accept the detent.

The detent 107 has a sloping tip which engages the selected holes with force which is sufficiently great to maintain the spring drive and blind at the given position when the blind is brought to rest at that position, and is sufficiently great to stop a very slowly moving blind at that position (that is, to stop the blind as a person slows movement of the blind to stop it proximate the position of the magnet.strips), but is sufficiently small (that is, the detent is sufficiently easy to dislodge from the selected holes) to stop the blind as it is raised and lowered at a normal speed.

j. Lar7e Dimension and Heav Window Cover Stems (FIGS. 38-41) FIGS. 38-41 illustrate examples of the use of spring drive units according to embodiments of the present invention in large window covers, for example, heavy covers or wide covers.

FIG. 38 depicts a single spring drive unit 15G which includes three lift cords and pulleys. The illustrated drive unit includes a spring drive such as 26, 31, 41 which is connected by a gear set 65 to the shaft on which the three lift cord pulleys 19 are mounted. Typically, the associated cords are routed along vertical paths which are spaced along the width of the wide and/or heavy cover, for uniform raising and lowering of the cover.

FIG. 39 depicts a window cover which includes a pair of drive units each of which is similar to that of FIG. 38, but includes two pulleys 19 and associated lift cords. The spring drives are connected by a power transfer bar unit 125 having bevel gear units 65 on the opposite ends which are connected to the rotating shaft of each spring drive, so that the drives, pulleys, and cords operate precisely in unison. The four illustrated pulleys 19 can be used to route four lift cords along vertical paths which are spaced along the width of the cover, for uniformly raising and lowering the wide and/or heavy cover (See FIG. 41).

I 1 107. Alternatively, referring to FIG. 37, holes at selected positions in the perforation-derived varied force spring may be of suitable size to accept the detent.

The detent 107 has a sloping tip which engages the selected holes with force which is sufficiently great to maintain the spring drive and blind at the given position when the blind is brought to rest at that position, and is sufficiently great to stop a very slowly moving blind at that position (that is, to stop the blind as a person slows movement of the blind to stop it proximate the position of the magnet.strips), but is sufficiently small (that is, the detent is sufficiently easy to dislodge from the selected holes) to stop the blind as it is raised and lowered at a normal speed.

j. Lar7e Dimension and Heav Window Cover Stems (FIGS. 38-41) FIGS. 38-41 illustrate examples of the use of spring drive units according to embodiments of the present invention in large window covers, for example, heavy covers or wide covers.

FIG. 38 depicts a single spring drive unit 15G which includes three lift cords and pulleys. The illustrated drive unit includes a spring drive such as 26, 31, 41 which is connected by a gear set 65 to the shaft on which the three lift cord pulleys 19 are mounted. Typically, the associated cords are routed along vertical paths which are spaced along the width of the wide and/or heavy cover, for uniform raising and lowering of the cover.

FIG. 39 depicts a window cover which includes a pair of drive units each of which is similar to that of FIG. 38, but includes two pulleys 19 and associated lift cords. The spring drives are connected by a power transfer bar unit 125 having bevel gear units 65 on the opposite ends which are connected to the rotating shaft of each spring drive, so that the drives, pulleys, and cords operate precisely in unison. The four illustrated pulleys 19 can be used to route four lift cords along vertical paths which are spaced along the width of the cover, for uniformly raising and lowering the wide and/or heavy cover (See FIG. 41).

I I, I FIG. 40 depicts a window cover comprising a pair of spring drive units 151 similar to the units 15G of FIG. 38, but with only one pulley 19 in each unit. This system is used for a two lift cord system, typically for heavy covers.

Finally, FIG. 41 depicts representative examples of the lift cord paths for two and four cord systems.

k. Plural Spring. Spring Drive System (FIGS. 43-45) FIGS. 43-45 depict a compact spring drive system 15J according to an embodiment of the present.mventin eandcomprising integrally formed plural spring drives. The spring drive system comprises plural (two or more) spring drives which share components and are aligned along the width of the associated blind. This integrated alignment provides force multiplication without increasing the size of the associated housing 11 and, specifically, without requiring a taller housing 11. Referring specifically to FIGS. 43 and 44, the illustrated two spring, spring drive system 131 comprises a first spring drive comprising storage drum or spool 132, common output or power drum or spool 136 and spring 133. The second spring drive comprises storage drum or spool 134, common output or power drum or spool 136 and spring 135. As perhaps best shown in FIG. 44, the spring 133 is routed from its storage drum 132 beneath the drum 134, from which point the two springs are routed together, with spring 133 under spring 135, over and around common output or power drum 136.

In effect, the individual torques of the plural springs are added together. The two storage spools are mounted for independent rotation so that outer spool 132 can rotate faster than inner spool 134. This is because the diameter of spring 133 on spool 136 is greater than the diameter of spring 135 and thus spring 133 rotates faster on its spool 132 than does spring 135 on its spool 134. Different types of springs can be used. For example, illustrated spring 135 is a conventional flat spring which provides substantially constant torque, and spring 133 is perforated so that the torque varies along the length of the spring proportional to the operational characteristics of the associated blind, as discussed previously. The combined springs provide a combined increased, varying torque sufficient for supporting heavy blinds, yet tailored to the different force requirements as the blind is raised and lowered.

FIG. 45 depicts one embodiment 15J of a spring drive unit which uses the two spring, spring drive' 131. The three spools 132, 134 and 136 are mounted on transverse shafts 81, 82, 91, respectively, spaced along the width (horizontally) of the associated housing 11. Gear 66 of gear set 65 is mounted on shaft 91 with the output or power spool 136 and meshes with gear 67, which is mounted on shaft 92 along with the cord pulley set 18 comprising right and left side cord pulleys 19, 19.

Of course, the other components such as transmissions 50 and 70 and bevel gear set can be used for transferring power from the spring drive to the cord pulleys and controlling the applied power, the travel of the blind relative to that of the spring drive, and the inherent, braking action. Furthermore, three or more springs can be used by the simple expedient of providing additional storage drums or spools and routing their associated springs together over and around the common output or power spool 136. For example, a third spring can be added to the drive 131, FIG.

43 and 44 by adding a third storage spool spaced generally horizontally to the left of spool 132, and routing the third spring beneath spring 133. Please note, as alluded to previously, this presents the opportunity to multiply the torque without increasing the size of the spools and the height of the housing 11. In contrast, in the plural spring system, the torque is increased by substantially a factor of two simply by adding a second spring the same size as the first spring. In effect, the increased spring mass required to multiply the torque can be provided by adding additional springs positioned along the horizontal axis of the spring drive, rather than by increasing the spring mass and spool diameter (and thus the height of the spool and the housing), as is the case where a single spring, spring drive is used.

In the embodiment shown in FIG. 45, the storage drums are arranged in a horizontal straight line, or approximately a straight line. In addition, both the output drum and the storage drums are arranged along the horizontal straight line.

Alternatively, the storage drums or both the output drum and the storage drums can be positioned along a vertical line. Alternatively, the storage drums can be arranged in a cluster, or both the output drum and the storage drums can be arranged in a cluster.

Similar to the single spring drive systems, in one embodiment, at least one of the flat springs is adapted for imparting a torque component to the system torque which varies along the length of that spring. In a specific embodiment, the said spring has a cove or transverse curvature which selectively varies along the length of the spring for providing the torque which varies proportional to the transverse curvature of that spring at a position closely adjacent the output drum.

Alternatively, the said spring has at least one hole therein for providing a torque proportional to the transverse size of the hole and the resulting effective width of that spring when the hole is positioned closely adjacent the output drum. In another alternative embodiment, the said spring has holes along its length for providing a torque which varies proportional to the transverse size of the holes and the resulting effective width of the spring when one or more holes is positioned closely adjacent the output drum.

It should be noted that the cover or blind housing which mounts the blind and the spring drive can be mounted along the bottom of the window or other surface to be covered, so that the blind extends upward for closing and retracts downward for opening. For convenience, in this document we describe the operation of top mounted, downward opening blinds and spring drives. However, it is understood that the invention is applicable to upwardly closing blinds, which typically have a bottom-mounted spring drive unit mount. The versatility of the spring drive system according to the present invention in adapting the spring torque characteristics to the operational characteristics of a given cover or blind as well as the braking action of the, make the system applicable to blinds of any operating orientation (top, bottom, lateral, etc.), weight and length.

The present invention has been described in terms of a preferred and other embodiments. The invention, however, is not limited to the embodiments described and depicted. One familiar with the art to which the present invention pertains will appreciate from the various carriers and blind/cover arrangements disclosed here, that the present invention is applicable in general to articles, objects or systems designed for support by and traversal along tracks. Adaptation of the system to other articles, objects and systems, including other blinds will be readily

SA

P:\OPER\ArlU608979spec page.doc-29/01/03 -26done by those of usual skill in the art. The invention is defined by the claims appended hereto.

Throughout this specification and claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

Claims (13)

1. A window cover system, comprising: an extendible window cover; a housing; lift cords attached to the cover and wrapped around rotatable pulleys mounted to the housing for raising and lowering the extendible cover; and a spring drive system connected to the lift cords for assisting the raising and lowering of the cover, the spring drive system comprising a flat spring drive mounted to the housing and having a first rotatable end and a second rotatable end; and a gear transmission of fixed ratio, the gear transmission operatively connected at one end via a bevel gear set to the second rotatable spring end and at the opposite end to the rotatable lift cord pulleys for rotating and being rotated by the lift cord pulleys, the gear transmission thereby applying the fixed ratio thereof between the flat spring drive and the lift cord pulleys, thereby controlling a force applied to the extendible cover by the flat spring drive.

2. A window cover system, comprising: an extendible window cover; a housing; lift cords attached to the cover and wrapped around pulleys mounted to the housing for raising and lowering the extendible cover; and a spring drive system operatively connected to the lift cords for assisting the raising and lowering of the extendible cover, the spring drive system comprising a flat spring drive mounted to the housing and having a first rotatable end and a second rotatable end; and a bevel gear set having one gear operatively connected to the second rotatable spring end and a second gear operatively connected to the lift cord pulleys for rotating and being rotated by the lift cord pulleys.

3. The window system of claim 1 or 2, wherein the flat spring drive has a torque or force which decreases as the extendible cover is lowered and increases as the extendible cover is raised, the flat spring drive applying the variable torque or force to the extendible cover. P :OPERRS%260M8979-2 a -28

4. A window cover system comprising: a base; an extendible window cover; and lift cords attached to the extendible cover and wrapped around pulleys mounted to the base for lowering and raising the extendible cover; and a spring drive system connected to the lift cords for assisting the lowering and raising of the extendible cover, the spring drive system comprising: a flat spring drive mounted to the base and having a first rotatable end and a second rotatable end, the second rotatable end applying a torque or force for assisting the lowering and raising of the extendible cover; and a variable transmission comprising a band or cord rotatably wrapped around two drums, a first of the drums being operatively connected to the second rotatable end of the flat spring drive for rotation therewith and the second drum being operatively connected to the lift cord pulleys for rotation therewith, the variable transmission having a ratio which varies as the drums thereof wind and unwind, thereby causing the lift cord pulleys to rotate at a rate that varies relative to the rate of the second rotatable end of the spring and varies the overall spring drive-to- pulley ratio.

The window cover system of claim 4, the variable transmission being operatively connected to the lift cord pulleys by a fixed ratio gear set comprising a plurality of intermeshed gears and having an input and an output and a fixed ratio between the input and output, the output being operatively connected to the lift cord pulleys for rotation therewith and the input being operatively connected to the second drum of the variable transmission for rotation therewith, to apply the fixed ratio of the gear set between the variable transmission and the lift cord pulleys.

6. A window cover system, comprising: a base; an extendible window cover; and lift means including a rotatable shaft mounted to the base, a plurality of pulleys mounted on the shaft for rotation therewith, and a plurality of lift cords wound around the pulleys and attached to the extendible cover for raising and lowering the extendible cover to selected positions; P \OPERRSH\2608979-2p doc. m3127 -29- a spring drive unit operatively connected to the lift means for assisting the raising and lowering of the extendible cover to selected positions, the spring drive unit comprising a spring drive mounted to the base and having a first rotatable end and a second rotatable end; and a gear transmission of fixed ratio; the gear transmission operatively connected between the second rotatable end of the spring drive and the lift means, thereby applying the fixed ratio of the gear transmission between the second rotatable end of the spring drive and the lift means, for altering the force applied between the spring drive and the extendible cover.

7. The window cover system of claim 6, wherein the spring drive comprises a flat spiral spring.

8. The window cover system of claim 6, further comprising: a variable transmission of substantially continuously varying drive ratio, operatively connected between the second rotatable end of the spring drive and the lift means, thereby applying the substantially continuously varying ratio of the variable transmission between the spring drive and the lift means for substantially continuously varying the force applied between the spring drive and the extendible cover.

9. The window cover system of claim 8, wherein the spring drive comprises a flat spiral spring.

The window cover system of claim 8 or 9, wherein the gear transmission is connected between the spring drive and the variable transmission, and the variable transmission is connected between the gear transmission and the life means.

11. The window cover system of claim 8 or 9, wherein the gear transmission is connected between the variable transmission and the lift means, and the variable transmission is connected between the spring drive and the gear transmission. P \OPER\RSH2608979-2spa do-73/2007

12. The window cover system of any one of claims 1 to 5, wherein the flat spring drive comprises a flat spiral spring.

13. The window cover system of any one of claims 1, 2, 4, 5 and 7, being substantially as described with reference to the drawings.