US2579144A - Winding and stopping mechanism for venetian blinds - Google Patents

Description

Dec. 18, 1951 F. GRIESSER 2,579,144

WINDING AND STOPPING MECHANISM FOR VENETIAN BLINDS Filed May 2, 1950 4 Sheets-Sheet l 3 FRITZ @R/ESSER AWN} PM firmmwsx Dec. 18, 1951 F. GRIESSER WINDING AND STOPPING MECHANISM FOR VENETiAN BLINDS 4 Sheets-Sheet 2 Filed May 2, 1950 F. GRIESSER 2,579,144

WINDING AND STOPPING MECHANISM FOR VENETIAN BLINDS Dec..18, 1951 4 Sheets-Sheet 3 Filed May 2, 1950 I 8322' 76 AWE/Wak- Dec. 18, 1951 F. GRXESSER 2,579,144

WINDING AND STOPPING MECHANISM FOR VENETIAN BLINDS Filed May 2, 1950 4 Sheets-Sheet 4 FIG-.15

Patented Dec. 18, 1951 WINDING AND STOPPING MECHANISM FOR VENETIAN BLINDS Fritz Griesser, Aadorf, Switzerland, assignor to Rolladenfabrik A. Griesser A.-G., Aadorf, Switzerland Application May 2, 1950, Serial No. 159,407 In Switzerland May 6, 1949 '7 Claims.

This invention relates to a winding and stopping mechanism for Venetian blinds and more particularly to apparatus for the operation, that is raising and lowering the laths of Venetian blinds and for maintaining them at the desired position.

According to the invention this operating mechanism comprises a winding shaft from which the laths of the blind are suspended and a driving device for said shaft, said driving device comprising two relatively movable members which are coupled with each other by means of a friction clutch in such manner that upon operation of the winding shaft for raising or lowering the laths the friction clutch is disengaged, while when the driving device is out of action and the winding shaft tends to turn under the influence of the weight of the laths or of a pulling action exerted thereon, a relative movement between said two members causes engagement of said friction clutch so as to prevent an undesired lowering of the laths.

In the accompanying drawings,

Fig. 1 is a vertical section through the winding shaft and the upper portion of a Venetian blind,

Fig. 2 is a plan view of the winding shaft assembly,

Fig. 3 is a transverse section through the casing of the winding shaft according to the line IIIIII of Fig. 1, drawn to a larger scale,

; Fig. 4 is a vertical section through the winding and stoppinggear,

Fig. 5 is a transverse section through the gear along the line V--'V of Fig. 4,

Fig. 6 is a vertical section through a window opening having a" Venetian blind according to the invention disposed outside of the window,

Fig. 7 is a similar sectional view of the upper part of a window opening with a modified disposie tion of the Venetian blind,

Fig. 8 shows the disposition of a Venetian blind at the interior of a sash window,

Fig. 9 is a vertical section of a modified arrangement of a winding shaft and gear,

. Fig. 10 is a plan view of the winding shaft and gear. assembly,

Fig. 11 is a transverse section through the easing of the winding shaft according to the line XIXI in Fig. 9,

Fig. 12 is avertical axial section through the winding and stopping gear,

Fig. 13 is a horizontal section through the gear with the movable parts shown in elevation,

Fig. 14 is a transverse section through the gear along the line XIV-XIV of Fig. 12,

Fig. 15 is a longitudinal vertical section through a further modified form of a winding shaft assembly, Fi g. 16 is a plan view of this modified form,

Fig. 17 is a transverse section along the line XVII-XVII of Fig. 15,

Fig. 18 is a transverse section through the Winding gear according to the line XVIII--XVIII of Fig. 1.

The Venetian blind according to Figs. 1-5 comprises an upwardly open casing I of U-shaped transverse section adapted to be mounted on the upper cross frame of a window opening. A wind ing shaft 2 extending through the entire length of the casing is rotatably mounted at both end walls of thecasing in fixed bearings 3 and 4. The shaft 2 carries two or more winding rolls 5.

A flexible pull member 6 for example a string, a

member 6 is fixed to the lowermost not represented lath. The provision of very thin steel tapes as pull members 6 is advantageous, since i when they wind up on the roll 5 they only slightly increase the diameter of the roll. The various laths of the blind are maintained between two bands II and i2 on cross straps l3 fixed to the bands and are maintained by the traversing pull members 6 against displacement in longitudinal direction. The carrier bands H and I2 of the laths l0 pass through the bottom of the casing l and the upper ends of each two cooperating opposite bands are fixed to a bracket l4 passing above the rolls 5. The two brackets M in the represented example are rigidly connected with tubes l5 and I6, and I6 and ll,respectively, which tubes are rotatable on the shaft 2. The two longitudinal edges of the brackets are bent backwards as shown in Fig. 3, while a slot [8 is provided at the bend through which slot pass the ends of the bands .H and I2 to be folded about a pin l9 and threaded again through the slot, so that when exerting a downwardly directed pulling action on the bands, they are automatically clamped within the bent portion of the bracket. When turning the bracket 14 in one or the other direction, one of the bands,- for example the band H, is pulled upwardly while the other band I2 moves downwardly. The laths H} can be brought in this manner in any desired inclined or almost vertical position as is shown in-dotted lines in Fig. 3. i

For operation of the winding shaft there is provided a winding gear located within a two part gear casing 20 carried at one end of the casing I. A bevel gear 2| is mounted within the casing 20 in alignment with the winding shaft 2 and is coupled with this shaft by means of a square socket cooperating with the square end 22 of 'theshaft. The gear 2| meshes with a second bevel--gear'23. This gear 23 comprises a hub 24 which is 'rotatably mounted in a fixed sleeve 25. A driver sleeve 21 is fixed by means of a pin 26 to the hub 24. A bolt 28 extends through the bore of the hub 24 to beyond the lower end of the hub for guiding a driving sleeve 29 which is freely rotatable relative to the bolt 28 and projects out of the casing 23. The portion of the sleeve 29 below the bolt 28 is provided witha square portion 3fiadapted to receive a driving member for the operation of the winding shaft 2. A coiled spring 3| is wound about the fixed sleeve 25. The driver sleeve 2! comprises a cylindrical wall portion 32 extending outside of the spring 3| through slightly less than one half of the circumference of the sleeve, while the sleeve 29 comprises a cylindrical wall portion 33 which extends substantially through one half of the circumference of the sleeve and penetrates into the space between the two end faces of the wall portion 32 of the sleeve 21. One end 34 of the coiled spring 3| bears against the end face 35 of the wall portion-33 of the sleeve 29. The other spring end 33 is bent backwards and at the bend the spring bears against the end face 3! of the wall portion 32 of the sleeve 21, while the free end of the bent spring portion cooperates with an abutment 38 of an extension 39 of the wall portion 32. The two sleeves 2! and 29 are movable relatively to each other, and the bent end piece 36 of the spring has a slight play between the two abutments 31 and 38.

When the blind has to be raised the coupling sleeve 29 is turned for example inthe direction of the arrow 0. in Fig. by means of a winding crank shaft to be inserted into the square socket 39. The sleeve 29 acts with the end face 33 of the wall portion 33 against the driver sleeve 21, 32 and causes this latter to turn in the same direction. The end face 31 of the wall portion 32 of this sleeve then acts against the bent portion of the spring end 38 and exerts pressure on the spring in the direction of opening of the spring coils. The spring 3| therefore can turn with the two sleeves 27 and 29- about the fixed sleeve 25. Rotation of the'sleeve 211s transmitted by means of the pin 26 to the bevel gear 23 which turns the gear 2| and accordingly the winding shaft 2. The two'rolls 5 turn with the shaft 2 and cause the two pull members 6 fixed thereto to be wound up about the rolls. The lowermost lath of the blind is raised by means of the pull member and abuts against the next following lath, and so forth. The blind can be raised in this manner entirely or into any desired intermediary position and remains then without else in the raised position as soon as the turning effort exerted on the sleeve 29 by means of the crank ceases. The rolls 5 and the shaft 2 obviously tend to turn in reverse direction, that is to say, in the direction corresponding to lowering of the laths, by the influence of the weight of the laths or under the action of a pulling force exerted on the laths, so that by the intermediary of the bevel gears 2| and 23 a turning effort in the direction of the arrow 1: in Fig. 5 is exerted on the sleeve 21, but now the abutment 38 of the sleeve 21 bears against the spring end 36 and exerts pressure on this spring end in the direction of closing of the spring coils about the fixed sleeve 25. The coils are clamped against this sleeve and form together with the sleeve a friction clutch which locks the driver sleeve 21 and accordingly the winding shaft 2 to the fixed sleeve 25 to prevent a movement of rotation of the shaft 2 in the direction of lowering of the laths.

When the blind has to be lowered, the sleeve 29 is rotated in the direction of the arrow b in Fig. 5 by means of the winding crank. Now the end face 35 of the sleeve portion 33 acts against the spring end 34 and exerts thereon a pressure in the direction tending to open the spring coils. The spring 3| can turn relatively to the fixed sleeve 25 so that the bent portion of the spring end 36 bears against the end face 31 of the portion 32 of the sleeve 2'! and transmits the movement of rotation of the sleeve 29 to the sleeve 21 and accordingly to the bevel gear 23. The shaft 2 now turns in the direction of lowering of the laths Hi. When the driving action on the sleeve 29 by means of the crank ceases, the shaft 2 tends to continue to turn in the same direction owing to the weight of the laths. The turning force in the direction of the arrow 11 is transmitted from the shaft 2 through thebevel gears 2| and 23 to the sleeve 21 and the abutment 38 of this sleeve at once bears against the free end of the spring portion 36 and exerts a pressure on the spring in the direction of closing of the spring coils so that the friction clutch becomes again operative. V

In order to tilt the laths I0 to inclined position the tube rotatable on the shaft 2 carries a screw wheel 40 meshing with a worm 4| which is rotatably carried outside of the gear casing 25. A driving pulley .42 carried by the worm shaft can be rotated by means of a string 43. .When pulling the string the screw wheel 40 andthe tubes I5, '|6, H with the brackets 54 connected to the wheel 43 can be swung in one or the other direction. In this manner one of the bands II or l2 carrying the laths is lifted and the other is lowered, and the laths are correspondingly inclined. The worm gear 40, 4| is not reversible so that the brackets |4 cannot move out of their adjusted position under the action of their weight. I i

For limiting the driving motion to raise or to lower the blind one end of the winding shaft 2 is provided with a screw thread 44. carrying a travelling nut 45 which ismaintained against rotation so that it moves longitudinally along the screw when the shaft 2 rotates. The movement of the nut 45 is limited in one direction by the bearing 3 and in the other direction by an adjustable abutment 46. This abutment is so adjusted according to the height of the blind or the number of the laths, that the sliding nut abuts against one or the other ofthe two abutments 3 and 46 when the laths are completely raised or completely lowered, so that a further operation of the winding gear by means of the crank driving the sleeve 29, when the blind has reached one or the other of its two endpositions, is not possible. This limitation of the winding operation is also necessary'in order to prevent a raising of the laths by rotation of the shaft 2 and the rolls 5 in the wrong direction-of rotation. The pull members 6 would naturally wind up on the rolls 5 in both directions of rotation thereof, but the frictionclutch forpreventing lowering of the laths by the action of their weight is only effective in one direction of rotation and it is accordingly necessary that the driving movement for raising or lowering of the blind can be efiected only in the correct-direction of rotation and thatthe pull members The gear casing 20 is carried by means of a bracket '41- on the casing l and canbe moved about the axis of the bevel gear 2! so thatthe driving shaft to be connected'to the square opening 30 f the driving sleeve 29 can be given the proper direction for its connection with the crank shaft as is represented in Figs. 6 and 7. .Fig. 6 shows anexample of a Venetian blind to which the winding and stopping mechanism according to the invention is applied. The blind having blades i0 is disposed outside of a window 48 in a recess 49. The casing 1 containing the winding shaft is fixed to the lintel in any convenient manner. The driving sleeve 25 projecting from the gear casing 2!! is connected to a square shaft 50 which is downwardly inclined and extends through the fixed window frame inside of which it is connected by means of an universal joint tothe manually operated crank shaft 52. The square shaft 56 is carried in a ball thrust bearing 53 in which it is maintained against disengagement from the square socket 30 of the sleeve 29. The crankshaft 52 is also carried by this bearing. The crankshaft 52 carries at its lower end a hingedly connected crank arm 54 to which the crank 55 is also hingedly connected.

For lowering or raising the blind the crankshaft 52 is swung to the position shown in dashand-dot lines in Fig. '6, in which a convenient manual operation of the crankshaft is possible. After operation of the blind the crankshaft 52 is returned to its position of rest drawn in full lines in which it depends perpendicularly from the universal joint 5|. The crank 54, 55 is then extended into aligned position with the shaft 52 so that in its position of rest the crankshaft together with the crank uses little space only but can be readily swung into operative position.

Fig. '7 shows a disposition of a Venetian blind immediately underneath the lintel 56.; A screen 51 covers the casing i and the raised laths of the blind towards the exterior. The driving sleeve 29 projecting from the gear casing 26 is again connected by an universal joint 5| with the crank shaft 52.

Fig. 8 shows a sash window having a Venetian blind disposed at the inside of the sash 58. 59 designates the box for the rolls on which the carrying cables of the sash are suspended. The

blind with the laths It! is suspended in the rear of the box 59. The crankshaft 52 adapted to be swung outwardly is again provided with hingedly connected crank members 54 and 55 andis connected by means of an universal joint 5i with the Winding gear located in the gear casing 20.

The example according to Figs. 9 to 14 comprises again an upwardly open casing l of U- shaped transverse section adapted to be mounted on the upper cross frame of a window opening. The winding shaft 2 is rotatably mounted in bearings -3 and 4 and carries winding rolls 5. To each 'roll 5 is attached one-end of a flexible pull member, particularly a thin steel tape. Each pull member passes through an opening Bil in the bottom of the casing l and over a guide roll 8 and penetrates through a hole 61 in each of the superposed laths H of the blind. The lower'end of the pull member 6 is attached to the not represented lowermost lath. The different laths of the blind are carried between two bands H and i2 on crossstraps l3'fixed to the bands. The bands H and 12. are suspended with their upper ends atchains 62- penetrating through slots 53 in the bottom of thecasing I and attached by their upper ends at suspension pins '64. The pins $4 of the chains of two cooperating bands ll and'l2 are carried by the ends of two arms 65' and 68-rigidly fixed to tubes 61 and 68. 2 These tubes canturn on the shaft 2 and are rigidly connected with each other by the pins 64 disposed symmetrically at both sides of the axis of the shaft 2. When the tubes 51 and 68 are turned and the arms 65 and 66 correspondingly tilted, the chains fixed for example to the band l2 are pulled upwardly and the chains fixed to the band I! are lowered, so that the two bands are displaced relatively to each other and the laths H) can be brought into any desired inclined position as is shown in dash-and-dot lines in Fig. 11. The stroke of tilting movement of the pin 6% is shown. in dash-and-dot lines in Fig. 11, and in the uppermost position of the pins, corre'- sponding to the closed position of the laths, the raised pair of chains 62 does not touch the winding shaft 2. 7

For actuating the winding shaft there is provided a winding gear located within a two-part gear casing ll]. A pair of bevel gears is mounted in this casing, the gear H of the'pair being disposed in alignment with the axis of the winding shaft 2, while the gear 12 is provided with a. hollow hub 13 having an interior square bore and extending out of the casing 10 for connections with a shaft member to be connected with the actuating crankshaft. The shaft M of the gear H also projects from the casing 10 and has its end carried in a bracket 51 fixed to the casing i, so that the casing 10 may be turned about the axis of the gear H and the winding shaft 2, permitting the hub 13 to be brought into any desired suitable position for connection with the crankshaft.

The gear H is coupled with the square end 15 of the winding shaft 2 by means of a friction clutch located within the casing 10. A disc I6 rigid with the gear H carries a driver member 17!. A bearing sleeve 78 is fixedto the casing '10 and serves as bearing for a driving sleeve 19 connected with the square end 15 of the shaft 2. ihe sleeve 79 is provided with a cylindrical skirt not extending over the entire circumference. The sleeve is guided by means of an axial plug Bl carried in a corresponding socket of the disc i5, and the driver 11 of the disc penetrates between the two ends or axial edges82, 82' of the interrupted skirt 80. A coiled spring 83 of rectangular wire section is wound about the fixed sleeve 13. One end 84 of the spring abuts with its rectangular end face against the driver I! on the disc 16, while the other end of the springgis bent back through 180, the bent over portion 85 being located in the space between the ends 82, 82' of the interrupted skirt B0. The free end of this bent over portion 85 abuts against the edge '82, of the skirt 88, while the bend of the. spring end cooperates with the edge 82 of the skirt 8G. The bent over spring end has a small play between these two edges. 7

When the blind is to be raised the gear pair I l, 12 is rotated by means of the crank shaft to be connected to the coupling sleeve 13, for example in such direction that the gear H with the driver 11 turns in the direction of the arrow 0. in Fig. 6. Thedriver 1'! acts in this case against the edge 82 0f the skirt while the edge B2 of this latter in turn acts against the bend of the spring end ,85 and exerts pressure on the spring83 acting to open the spring windings. Accordingly, the spring can turn about the fixed bearing sleeve 78 together-with the, skirt 80 and the sleeve [9. This latter transmits the movement of rotation to the square end 15 of the winding shaft 2 which is turned in the direction to wind up the pull member 6 on the rolls turning with the shaft, and to raise the laths.

As soon as the driving action exerted by means of the crank shaft on the gear pair II, I2 ceases, the laths remain stationary in the raised position. The weight of the blind exerts a turning moment on the rolls 5 tending to turn the sleeve I9 with'the skirt 80 in the direction of the arrow 12 in Fig. 6, but now the edge 82 of the skirt 8i! acts against the free end of the bent-over spring portion 85 and effects a closing of the spring coils about the fixed sleeve 18. The spring windings are clamped about the sleeve and form together with the sleeve a friction clutch which couples the sleeve 79 and the winding shaft 2 with the fixed sleeve 18 so as to Prevent any rotation of the shaft 2 in the direction corresponding to lowering of the blind.

When the blind shall be lowered, the crank connected with the sleeve 13 is rotated to turn the gear II in the direction of the arrow in Fig. 6. Now the driver TI acts against the spring end 84 and exerts on this, latter a pressure in the direction to open the spring coils. The spring can turn about the fixed sleeve I8 so that the bend of the spring end 85 acts against the edge 82 of the skirt 80 and transmits the movement of rotation of the driver 11 to the skirt and to the sleeve 19. The shaft 2 is now turned in the direction corresponding to lowering of the blind. As soon as the driving action exerted on the shaft by the crank through the intermediary of the bevel gears ceases, the laths are stopped. The shaft 2 which, owing to the weight of the blind, tends to continue its rotation in the same direction, exerts .a turning moment in the direction of the arrow b in Fig. 6 on the sleeve T9. The edge 82 of the skirt 8B is thus applied against the free end of the bent-over spring end 85 and exerts a pressure on the spring in the direction corresponding to closing of the spring coils, so that the friction clutch again becomes active.

For tilting the laths I0 into their inclined or closing position, the tube 61, which is rotatable on the shaft 2, is rigidly connected wtih a worm wheel 40 meshing with a worm 4| which is rotatably mounted outside of the gear casing 18. A driving pulley 42 is carried by the worm shaft and can be turned by means of a string 43. By pulling the string, the worm wheel 40 and the tubes 61, 68 together with the arms 65, 66 and the pins 64, can be turned in one or the other di rection. One of the bands H or I2 carrying the laths is raised and the other lowered and the laths are accordingly brought to an inclined position.

The exampleaccording to Figs. -18 comprises again an upwardly open casing I of U-shaped cross section. The winding shaft 2 is rotatably mounted within the casing and carries winding rolls 86 to each of which a thin steel tape is connected. The tape 6 penetrates through an open ingin the casing I and through an opening in each of the superposed laths ID to be attached to the lowermost not represented lath. The laths are again carried by bands I I connected by means of chains 62 to pins 64 which are carried by rocking arms, .66. These arms are rigidlyconnected to a rotatable tube 68 which in turn is connected to, a, second pair, of arms carrying further lath supporting bands II. The chain 62 traverse openings 63 in the bottom of the casing I.

At one end of the shaft 2 there is provided a friction clutch located within a casing 10 which is fixed .to the casing I by means of an angular bracket 81. The end of the shaft 2 is formed by a square plug I5 which is inserted in a corresponding square recess of a driving sleeve 19. The latter is rotatably mounted in a fixed bearing sleeve 18 carried by the casing I0. A coiled spring 83 of rectangular wire section is wound about the fixed bearing sleeve "I8. The driving sleeve I9 is provided with a cylindrical skirt not extending through the entire circumference of the sleeve. The sleeve I9 is guided by means ,of a cylindrical plug 8| in a corresponding recess of a disc 16 having a driver TI (Fig. 16). This driver 2| extends into the free space between the two axial edges of the interrupted skirt 80. One end 8 4 of the spring 83 bears against the driver I1, while the other end 88 of the spring is thickened to cooperate with both axial edges'of the skirt 8!). The disc 16 is connected with adriving shaft 89 disposed in alignment with the shaft 2. The free end of the shaft 89 extends out of the casing 10 and is fixed to a hub 96 by means of a screw 9!. This hub is rigidly connected with a driving wheel 92 disposed outside of the end of the casing I. The driving wheel is provided with a circumferential groove 93 which is subdivided by uniformly spaced cross webs 94. A flexible pull member 95 is engaged in the groove 93 and is formed of balls which cooperate with the webs 94. The pull member passes over guide rolls 96 and is preferably endless.

The operation of the blind by means of the wheel 92 is identical with the operation by means of the crank as described with reference to Figs. 12 to 14, except that no bevel gears are necessary. The driving movement is transmitted directly from the wheel 92 and the shaft 89 to the driver I1. When the driver is turned in one or the other direction, the driver 11 or the skirt 80 act on the spring 83 in a direction to open the spring coils and allowing rotation of the sleeve 19 and accordingly of the winding shaft 2, while a turning moment originating from the weight of the laths and exerted on the sleeve I5, results in tightening the spring coils about the fixed sleeve 18, so that the friction clutch becomes effected and maintains the blind in the position to which it has been brought.

I claim:

1. Venetian blind operating mechanism, comprising a rotatably mounted winding shaft, flexible lath raising and lowering members suspended from said shaft and adapted to wind-up on the shaft or unwind therefrom upon rotation of the shaft, driving means operatively connected to said shaft for rotating the shaft in one or the other direction, and a friction clutch connecting said driving means to said shaft, said friction clutch including a resilient member, said friction clutch through said resilient memher being operative to allow rotation of said shaft in either direction when actuating said driving means, but preventing rotation of the winding shaft under the action of a turning effort exerted on the shaft by the weight of the laths sus-, pended therefrom. -.2. Venetian blind operating mechanism, com- 9 prising a rotatably mounted winding shaft, flexible lath raising and lowering members suspended from said shaft and adapted to wind-up on the shaft or unwind therefrom upon rotation of the shaft, driving means operatively connected to the winding shaft for rotating the shaft in one or the other direction a friction clutch connecting said driving means to the winding shaft, said friction clutch including a relatively fixed sleeve, a coiled spring wound about said sleeve, a driving sleeve member coacting with one end of said spring, a driven sleeve member mounted for rotation with said winding shaft and coacting with the other end of said spring, and with said- .driving sleeve, whereby upon actuation of said driving means for raising or lowering the laths one of said sleeve members acts against the corresponding spring end in a direction to open the spring coils to allow rotation of the spring about said fixed sleeve, while a turning effort exerted on the winding shaft by the action of the weight of the laths and transmitted to said driven sleeve member acting against the corresponding spring end in a direction to close the spring coils about said fixed sleeve to prevent rotation of the spring.

3. Venetian blind operating mechanism as defined in claim 2, wherein the spring end cooperating with said driven sleeve member has a thickened end portion coacting with two opposed abutment faces of said sleeve member, whereby U when the sleeve member tends to turn in one direction it acts against the spring end to open the spring coils, and when the sleeve member tends to turn in opposite direction it acts on the spring end to tighten the spring coils about said fixed sleeve.

4. Venetian blind operating mechanism, comprising a rotatably mounted winding shaft, flexible lath raising and lowering members suspended from said shaft and adapted to wind-up on the shaft or to unwind therefrom upon rotation of the shaft, a driving member for actuating said winding shaft, a driving gear for transmitting movement of rotation from said driving member to said winding shaft, said driving gear comprising a pair of bevel gears, and a friction clutch including a resilient member connecting said driving member to said bevel gears, said friction clutch through said resilient member being disengaged when said driving member is 5 operated to turn the winding shaft but becoming effective to prevent rotation of the winding 10 shaft under the action of the weight of the laths suspended from the shaft.

5. Venetian blind operating mechanism, comprising a rotatably mounted winding shaft, flexible lath raising and lowering members suspended from said shaft and adapted to wind-up on the shaft or to unwind therefrom upon rotation of the shaft, a driving member for actuating said winding shaft, a driving gear for transmittin movement of rotation from said driving member to said winding shaft, said driving gear comprising a pair of bevel gears, and a friction clutch interposed between said pair of bevel gears and one end of the winding shaft, said friction clutch including a relatively fixed sleeve, a coiled spring wound about said sleeve, a driver on one of said bevel gears and coacting with one end of said spring, a rotatable driven member mounted for rotation with the winding shaft and coacting with the other end of said spring and with said driver, whereby said spring coils are loosened from said relatively fixed sleeve upon actuation of the driving member to raise or lower the laths, and tightened about said sleeve to lock said bevel gears upon a turning effort resulting from the weight of the laths being exerted by the winding shaft on said driven member.

6. Venetian blind operating mechanism as claimed in claim 5, wherein said pair of bevel gears and said friction clutch are lodged in a cas- FRITZ GRIESSER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,029,143 Wicks Jan. 28, 1936 2,231,778 Swanson Feb. 11, 1941 2,276,716 Cardona Mar. 17, 1942 2,324,536 Pratt July 20, 1943

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