DRIVING MECHANISM FOR A BACKDROP

Abstract: The invention relates to a driving mechanism for a backdrop, in which the board roll (10) is attached to two brackets (3a, 3b) supported by pivots (8, 17). The brackets are suspended from a rope system (2) which passes along the vertical guides (1a, 1b) and their inter-connecting cross-bar and through the rolls, and which has been adapted to lift and lower the board roll remaining in horizontal position. By pulling at the ropes, the brackets will rise, causing the drive roll (7) of the board roll to roll out of frictional contact with the vertical guide (1a) along the guide and board is to be unwound from the roll (10). The board roll is lowered by releasing the rope system, so that the rotation of the drive roll in the opposite direction along the guide causes the board roll to be rewound. In accordance with the invention, before the roll is raised, a board end can be pulled out to the floor from the roll, without clamping the board roll on the support pivots (8, 17), leaving the roll free to rotate when the board end is pulled by hand, although the drive roll is in frictional contact with the guide. To rewind the board end extending to the floor after the photographing session, the drive roll (7) is brought out of frictional contact with the guide by turning the bracket (3a) counter-clockwise about the axle of the glide roll (14a) with the lever (4), supported by the support surface between the guide (1a) and the glide roll and acting against the force of the spring (15), and the board roll can be wound with the handle (9), thus rewinding the roll end onto the roll.

Description: Driving mechanism for a backdrop The application relates to a driving mechanism as defined in the preamble of claim 1. Such a backdrop is widely used especially in photographers' studios in order to provide for a photographic background with the desired colour and any desired background pattern. Backdrops are supplied in rolls having a roll core onto which the board is wound. Board rolls have a standard length, 272 ± 3 cm, their full outer diameter is approx. 9.5 cm and they contain about 11 m of board. The rolls are consequently very heavy and awkward to lift on their stands. A backdrop is usually used so that it first follows the floor and then rises in a curve of long radius up to a height allowing the photographed object to be placed on the vertical dimension of the board. This arrangement makes the boundary between the horizontal face and the vertical face invisible in the picture, because there is no bending point in the board background, but only a portion generating a change of direction with a slowly sloping curve. One photographic session usually requires only part of the entire length of the roll, the remainder of the roll and the roll core being at the upper edge of the backdrop, where it is supported by some kind of driving mechanism. The portion resting on the base is at least partly fouled during photographing, because the object is placed on it. This fouled portion is usually not reusable, but is cut off, whereas the remainder is reused, being rewound after the session and stored for ultimate use. Photographers have a large number of different backdrops at their disposal, which, whenever necessary, they fasten to the driving mechanism, use as described above and remove from the driving mechanism after use. German patent specification 196 452 describes a driving mechanism for a backdrop, in which the board roll is lifted in its vertical stand upwards from its mounting position, the board being unwound, and downwards, the board having served as a backdrop being rewound by a manually operated rope system. The ends of the board roll are in frictional or gear contact with vertical guides so that the roll is unwound each time it is raised into upper position in the stand by means of the rope system, and the released board is rewound when the roll is lowered. The conventional driving mechanism enables the roll to be easily raised in upper position while releasing the backdrop, and to be lowered into the initial position after the photographing session while the board is being rewound. As described above, in current applications, the board is pulled down to the floor and over a distance on the floor, so that the board forms a slowly sloping background. The conventional device does not enable such an excess board end to be pulled on the floor before the lifting of the roll is started. Nor does the conventional device enable the end on the floor to be rewound. Currently used board roll stands do not comprise any kind of automation, the roll supports with their expandable pivots being fixed at the desired height, and after this the photographer fastens the heavy roll first to one support and then to the other while standing on a ladder. The desired amount of board is pulled off the roll and temporarily fixed with a tape to the floor surface, forming a suitable background curve. At the end of the photographing session, any fouled board portion is cut off and the remainder of the released board is rewound with the roll in upper position. Finally, the roll is removed from its upper position and taken to storage. Such an operation is slow, heavy and hazardous. The purpose of the present invention is to provide a safe driving mechanism for a backdrop, allowing the board end placed on the floor to be readily and rapidly pulled out from the roll before photographing and to be rewound as readily after photographing or for replacement of the roll. A second objective of the invention is to provide a driving mechanism which is straightforward and easy to manufacture, and which is easy and rapid in use. In accordance with the invention, these objectives are attained by imparting the driving mechanism as defined in the preamble of claim 1 the characteristics defined in the characterising clause of claim 1. In the driving mechanism of the invention, each of the brackets supporting the board roll and rolling in vertical guides thus forms a rigid casing-like design comprising two side walls, the vertical guide being adapted to pass between these in operating position. A support pivot supporting the board roll has been rotatably secured to the side walls of the bracket on one side, i.e. the front side of the vertical guide, and the glide has been rotatably fixed on the other side, i.e. rear side of the vertical guide. The rope supporting the rope system bracket is fixed to the upper part of the bracket, close to its rear edge. The glide surface facing the vertical guide contacts the vertical guide. At least in one bracket, i.e. the driving bracket, a drive roll has been journalled on the support pivot axle, into driving contact with the support pivot. In the lifting and lowering step of the brackets, the weight of the board roll and the mutual position of the glide means, the pivot supporting the board roll and the vertical guide bring the board roll into frictional contact with the vertical guide causing it to roll on the vertical guide as the brackets are being raised and lowered. On the front side of the non-driving bracket, at least one glide means is provided, which is in contact with the vertical guide in the lifting and lowering step in order to stabilise the bracket relative to the vertical guide. Such a bracket design has an important additional characteristic, i.e. it allows the driving bracket to be rotated relative to the fixed glide axle, bringing the drive roll out of frictional contact with the vertical guide and enabling the board roll to be rewound by hand with the aid of a winding means solidly fixed to the drive roll. The other bracket, which preferably is non-driving, has been adapted such that its supporting pivot can be fitted into the winding core of the board roll, the other roll end being already fitted on the support pivot of the drive roll. This is preferably arranged such that the non-driving bracket can be brought out of contact with the vertical guide for instance by providing a slot in the inner side wall or by making the support pivot removable from the inner bracket wall. The drive roll of the driving bracket preferably has a rolling diameter almost equal to the diameter of the board roll. Thus the rolling rate of the board roll is approximately equal to the peripheral speed of the board roll, the board being wound in synchronism with the rolling of the board roll on the vertical guides. The glide means preferably have the form of rolls. The glide roll provided on the rear side of the driving bracket bears on the vertical guide on the tangential line between the vertical guide and the glide roll when the driving bracket is rotated about the axle of the glide roll and the drive roll fixed to the bracket is forced out of contact with the vertical guide. The glide means may optionally be a slide block whose one surface bears on the vertical guide. The support surface is preferably concave and matches the cylindrical mantle surface of the vertical guide. Then the rotation of the bracket spins about the axle of the slide block while the support face of the slide block bears against the vertical guide. Mainly because of manufacturing techniques, the two brackets are preferably identical, however, with the difference that the front roll of the non-driving bracket is not in frictional contact with the vertical guide. It is preferable that the front roll of only one of the brackets is in driving frictional contact with the vertical guide, because then the other bracket may glide and yield relative to the vertical guide whenever necessary. For the same reason, the board roll is preferably placed on the support pivot of the non-driving bracket without clamping, thus providing better yield for instance if the stand is slightly tilted or asymmetric or the winding core of the roll is distorted. In the bracket, the axle of the support pivot is lower than the axle of the glide member in the operating position of the bracket. This enhances the frictional contact between the drive roll and the vertical guide. The surfaces contacting the vertical guide are preferably slightly concave in crosssection, matching the circumferential surface of the cylindrical vertical guide. This provision stabilises the operation of the driving mechanism of the invention. The drive roll and the vertical guide are in driving frictional contact with each other. Only one of the contacting surfaces, preferably the circumferential surface of the drive roll, is a frictional surface. The side wall of the non-driving bracket facing the board roll is preferably divided into two parts, thus providing a slot having a width larger than that of the vertical guide between the axial points of the glide and the front roll, parallel to the vertical bracket sides. The bracket can then be brought out of contact with the vertical guide through this slot, hanging freely from the rope, and its support pivot is easy to fit into the winding core of the board roll. The driving bracket is preferably equipped with a spring, which in the normal operating state forces the bracket in the direction of rotation, in which the board roll is stretched against the vertical guide, and which is compressible by hand, the bracket then rotating in the opposite direction and bringing the drive roll out of driving frictional contact with the vertical guide. One end of the spring is preferably attached to the wall structure of the bracket, and the other end is attached to an arm articulated in the wall, the end of the arm bearing against the vertical guide over a disc. The bracket preferably comprises a lever, by means of which the bracket is rotated against the spring force in order to detach the drive roll from the vertical guide. This enables the user to rewind the board end hanging from the board roll using a handle connected to the support pivot with his other hand. A driving mechanism with such a design allows a backdrop roll to be very easily and rapidly replaced and raised to the desired height, the background curve desired for photographing to be provided and the board length to be recovered after photographing to be rewound on the roll. The operation takes about a minute and does not involve any risks, whereas the conventional operation used to take up to 15 minutes and to involve both heavy and hazardous work steps. A number of preferred embodiments of the invention are explained below with reference to the accompanying drawings, in which figure 1 is a schematic perspective front view of the driving mechanism of the invention, i.e. viewed from the board roll, with the vertical guides in section at their upper and lower end and one wall of the driving bracket partly removed; figure 2 is a lateral view of the drive roll side of the driving mechanism of figure 1 on a smaller scale, in a step where the board is pulled out on the floor while the board roll is freely rotating on the support pivots; figure 3 shows the driving mechanism of figure 2 in a step where the lifting of the board roll by means of a rope system is started; figure 4 shows the driving mechanism of figure 2 (with part of the vertical guide removed) in a step where the board roll is in photographing position and is started to be lowered; figure 5 shows the driving mechanism of figure 2 in a step where the board roll is in its lower position with the rope system blocked and the bracket rotated counter-clockwise in order to remove the drive roll from frictional contact with the vertical guide, and where the winding of the board roll by means of the handle has started in order to wind in the released board length; figure 6a is a lateral projection of the bracket of a driving mechanism of a second embodiment and its drive roll in driving contact with the vertical guide; figure 6b is a lateral projection of the bracket of figure 6a in non- ving position; figure 7a is a lateral projection of the non-driving bracket of the driving mechanism of figure 6 and its front roll in operating position; figure 7b is a lateral projection of the bracket of figure 7a in detached position; figure 7c is a top projection of the removable bracket of figures 7a and 7b and part of the board roll; figure 8a is a lateral projection of the bracket of the driving mechanism of another embodiment and its driving roll in driving contact with the vertical guide and part of the inner wall removed; figure 8b is a lateral projection of figure 8a, where the driving roll is brought out of frictional contact with the vertical guide; and figure 8c is an axonometric enlarged view of the glide means of figures 8a and 8b. Figure 1 is an axonometric and schematic view of the driving mechanism of the invention. The vertical guides la and lb bear against the base over the leg structure of the stand and the vertical guides are connected by a not represented horizontal bar attached to the guides from the top. At the two upper corners of the stand, there are wheels, over which the rope system 2 runs from the fasteners 6a, 6b in the brackets 3a and 3b of the board roll 10 into the rope clip. The fasteners are fixed to pins 36b connecting the bracket walls 12a and 13a and 12b and 13b, respectively, figures 1 and 7c. The rope system is not shown in detail, because it is of a type known per se. The bracket 3 a shown on the left in the figure is called driving bracket, because it comprises a drive roll 7 which is in driving frictional contact with the vertical guide la. The bracket 3b on the right is called non-driving or removable bracket, because its wall 13b facing the board roll has a vertical slot 5 for removal of the bracket from the vertical guide lb and thus also for removal of the bracket from the winding core 11 of the board roll. The brackets are formed of two interconnected side walls 12a and 13a, and 12b and 13b, respectively, the walls 13a and 13b being the inner walls of the brackets. The vertical guides la and lb pass between the bracket walls and divide the brackets in a front part, in which the board roll is fitted, and a rear part. On the front side of the driving bracket 3 a, between the walls 13a and 13b, a drive roll 7 and a firmly attached expanding support pivot 8 have been journalled. The clamping of the support pivot is performed by means of a spindle 18. The rolling surface of the drive roll has an efficient friction surface, e.g. a rubber coating (not shown). On the rear side of the bracket 3a, higher than the drive roll, a slide block in the form of a disc 14a has been mounted on bearings. On the rear side of the driving bracket 3 a, below the driving roll axle, a spring 15 has been attached in order to force the bracket clockwise, pressing the drive roll 7 against the vertical guide. One end of the spring 15 is attached to the bracket 3a and the other end to an arm 16 articulated in the bracket, the free end of the arm comprising ajoumalled disc bearing against the vertical guide la. The driving bracket 3a comprises a lever 4 fixed e.g. to the wall 12a, the lever serving to compress the spring 15 and to rotate the bracket counter-clockwise about the axle of the slide disc 14a while the rolling surface of the disc bears against the vertical guide la in order to remove the drive roll 7 from frictional contact with the vertical guide. The drive roll 7 comprises a fixed handle 9, by means of which the board roll clamped on the support pivot 8 can be wound when the drive roll is brought out of frictional contact with the vertical guide. The non-driving bracket 3b has approximately the same construction as the driving bracket 3 a. Between the walls 12b and 13b, on the rear side of the bracket, a rope loop 6b and a glide in the form of a disc 14b are fastened. A board roll support pivot 17, which is not necessarily expandable, is solidly mounted on the front side of the bracket. It is rather preferred that the board roll rotates freely about the support pivot 17, thus compensating any inclinations and distortions as one end of the board roll is allowed to move freely about its support pivot. A pin spindle 19 is fitted on the support pivot axle 20. No wheel corresponding to the drive roll has been journalled on the support pivot axle 20, however, a glide disc 21 has been mounted on bearings below the axle. In the operating position of the bracket 3b, the discs 14b and 21 bear against the vertical guide lb under the effect of the torques exerted by the bracket. All of the discs 14a, 14b, 16 and 21 spinning in the brackets preferably have a concave circumferential surface in order to provide a firmer contact with the vertical guide. The circumferential surface of the drive roll 7 is preferably also hollow. The inner wall 12b of the bracket 3b comprises a vertical slot 5 having a width slightly larger than that of the vertical guide lb. The bracket 3b can thus be brought out of contact with the vertical guide by positioning it vertically and detaching it from the vertical guide by passing it through the slot while pulling the support pivot 17 out from the winding core 11 of the board roll. Figures 2-5 show different positions of the board roll 10 in the driving mechanism, illustrating the driving bracket 3 a in the vertical guide la and the free end 100 of the board roll viewed laterally. Before the situation shown in figure 2, the board roll is fitted in both brackets 3a and 3b. The brackets are at a level allowing the roll to be readily lifted and secured. The rope system is adapted in a manner known per se to retain the brackets constantly at the same height. The left-hand end of the roll is pushed on the support pivot 8 of the driving bracket and the left-hand end on the pivot 17 of the non- driving bracket 3b detached from the vertical guide, and subsequently the non- driving bracket is fitted on the vertical guide 3b through its slot 5. The board roll 10 has not been clamped on the support pivots 8, 17 and can thus rotate freely, even if the bracket is in frictional contact with the vertical guide under the effect of the weight of the roll and the spring 15. The user grasps both ends of the board roll and pulls it to form the desired background curve, and then attaches the board end for instance with a tape T to the base 101. Figure 3 shows the start of the lifting step of the board roll. Before being lifted with the rope, the roll is clamped on the support pivot 8. Then the rope(s) is (are) released from the rope clip and pulled downwards, causing the brackets 3a and 3b to rise and the drive roll 7 to roll counter-clockwise upwards on the vertical guide la. The board is unwound from the roll at the same rate as the roll rises upwards in the stand, because the outer diameter of the roll is approximately equal to the rolling diameter of the drive roll 7. As the roll decreases, the unwinding rate slows down somewhat, resulting in a correspondingly smaller amount of unwound board. However, the change in the board roll diameter is relatively small, because the board laps are then relatively thin compared to the winding core diameter of the board roll. The roll is placed at the desired height, where the rope is fastened to the rope clip. The background is now ready for photograpliing, the situation shown in figure 4. The board roll is removed in the inverse order. The rope is unfastened and the brackets are lowered, which happens automatically under the weight of the roll. The lowering motion is slowed down by hand with the use of the ropes. As the brackets move downwards, the drive roll rolls clockwise and rewinds the board onto the roll at the same rate. As the board roll reaches the desired height, the rope is blocked in the rope clip and the bracket 3a is turned counter-clockwise by pressing down the lever 4 so that the spring 15 is compressed and the drive roll 7 is brought out of contact with the vertical guide la. At the same time as the user presses down the lever 4, he grips the handle 9 and rotates the drive roll which is out of frictional contact, and then the released board length is rewound onto the roll, the situation shown in figure 5. The roll is removed from the stand by releasing the hold of the expanded support pivot 8 about the winding core and by removing the right-hand bracket 3b from the vertical guide and the support pivot 17 from the winding core 11. The user now holds the roll conveniently with his two hands, and pulls it off the support pivot 8, thus removing it from the stand. Figures 6-8 illustrate a simplified embodiment of the driving mechanism of the invention. Figures 6a and 6b show the driving bracket in operating position and in a position brought out of frictional contact, respectively; figures 7a and 7b show the non-driving bracket in operating position and in detached position, and figure 7c the non-driving bracket of figures 7a and 7b from the top and the roll in cross-section; figures 8a and 8b illustrate the driving bracket equipped with a slide block and figure 8c is a perspective projection of the slide block. The driving bracket 33a comprises two rectangular side walls, with a drive roll 27 journalled between the walls on the front side of the bracket and a glide roll 34a on the rear side of the bracket. The bracket does not comprise any spring enhancing frictional contact. By contrast, the drive roll is journalled in the vicinity of the outer edge of the bracket 33a and slightly lower than the glide roll, forming a relatively large zone between the rolling surfaces of the glide roll and the drive roll, the zone having a width e.g. equal to the diameter of the glide roll. The rope system 2 is fastened on the rear side of the bracket, at the upper corner. This arrangement ensures that the drive roll 27 is pressed against the vertical guide with a strong torque. The bracket 33a is brought out of frictional contact by pressing the lever 24, as shown in figure 6b, the bracket then spinning about the axle of the glide roll 34a while the rolling surface of the glide roll bears against the vertical guide la. The released board length is rewound onto the roll by ftirning the handle 29. Figures 7a, 7b and 7c show the non-driving bracket 33b of the same embodiment. The bracket 33b is identical to the bracket 33 a, however, with the difference that the inner wall 43b of the bracket 33a comprises a slot 5. In terms of manufacturing techniques, this solution is an advantageous one. The driving bracket 33a has been equipped with a lever 24 and a handle 29. Figure 7c is a top view of the driving mechanism of figures 7a and 7b, with the board roll viewed in cut section. The driving mechanism of this embodiment is used in the same manner as the mechanism of figures 1-5. Figures 8a-8c show the non-driving bracket of figure 6b, which has been equipped with a glide means in the form of the slide block 44a. The surface of the slide block facing the vertical guide is made hollow so as to match the cylindrical mantle surface of the vertical guide. Figure 8c is a perspective view of the slide block 44. When the drive roll 27 is brought out of frictional contact with the vertical guide, the bracket spins about the axle of the slide block, while the concave stop face of the slide block bears against the vertical guide. Similarly, the glide roll of the non- driving bracket can be replaced with a body like the slide block 44a.

Claims: Claims 1. A driving mechanism for a backdrop comprising a vertical stand including two vertical guides (la, lb), two brackets (3a, 3b; 23a, 23b) supporting a board roll (10) at its ends and adapted by means of a rope system (2) to pass on the vertical guides so that the board roll is unwound as it moves upwards and the released portion is rewound on the roll as the roll moves downwards, characterised in that the two brackets (3a, 3b; 23a, 23b) are formed by a rigid casing-like construction comprising two side walls (12a, 13a, 12b, 13b), between which the vertical guide (la, lb) is adapted to pass in operating position and to which the support pivot (8, 17) of the board roll (10) has been rotatably fastened on one side, i.e. the front side of the vertical guide and on which a slide means (14a, 14b; 34a, 34b; 44a) has been rotatably fastened on the other side, i.e. the rear side of the vertical guide, the rope system (2) being attached (6a, 6b) to the upper portion of the rear side of the bracket; that the surface of the glide means (14a, 14b; 34a, 34b; 44a) facing the vertical guide (la, lb) is in contact with the vertical guide and that at least one bracket, i.e. the driving bracket (3a; 23a) comprises a drive roll (7; 27) journalled in driving contact with the axle of the support pivot (8), the drive roll being in frictional contact with the vertical guide (la) in the rising and lowering step so as to roll on the vertical guide as the bracket (3 a; 23 a) is lifted or lowered; in that the second bracket (3b; 23b), i.e. the non-driving bracket, comprises, on its front side, at least one glide means (21; 41) which in the rising and lowering step of the bracket is in contact with the vertical guide (lb); that the driving bracket (3a; 23a) is rotatable about the axle of the attached glide means (14a; 34a), bringing the drive roll (7; 27) out of frictional contact with the vertical guide (la); that the drive roll (7; 27) is firmly connected with a winding means, preferably a handle (9; 29), for manual winding of the board roll (10); and that the hold of the other bracket (3b; 23b) about the vertical guide (lb) can be released or the support pivot (17) can be removed from the space extending towards the board roll (10) for the still free end of the board roll to be placed in this bracket. 2. A driving mechanism as defined in claim 1, characterised in that the board roll (7; 27) has a rolling diameter equal to the diameter of the board roll (10). 3. A driving mechanism as defined in claim 1 or 2, characterised in that one or more of the glide means have the form of a roll (14a, 14b, 21; 34a, 34b; 41). 4. A driving mechanism as defined in one or more of claims 1-3, characterised in that the non-driving (23b) and driving (23a) brackets are identical, however, with the difference that the roll (41) on the front side of the non-driving bracket is not in frictional contact with the vertical guide (lb). 5. A driving mechanism as defined in one or more of claims 1-4, characterised in that the axle of the drive roll (7; 27) and the support pivot (8) is located below the axle of the glide means (14a; 34a; 44a) in the bracket. 6. A driving mechanism as defined in one or more of claims 1-5, characterised in that the rolling and glide surfaces respectively of the wheels, discs and the slide block contacting the vertical guides (la, lb) are slightly concave in cross-section, matching the circumferential surface of the circular vertical guide. 7. A driving mechanism as defined in one or more of claims 1-6, characterised in that either one of the contact surfaces of the drive roll (7; 27) and the vertical guide (la) is a frictional surface. 8. A driving mechanism as defined in one or more of claims 1-7, characterised in that the side wall (43b) of the non-driving bracket (23b) facing the board roll is divided into two parts so as to provide a slot (5) preferably parallel to the vertical sides of the bracket between the axial points of the glide means (34b) and the front roll (41), the slot having a width larger than that of the vertical guide (lb). 9. A driving mechanism as defined in one or more of claims 1-8, characterised in that the driving bracket (3a) is equipped with a spring (15), which in the normal position of the driving mechanism forces the bracket (3 a) into the direction of rotation, in which the drive roll (7) is pressed against the vertical guide (la), and which can be compressed by hand, the bracket (3 a) then rotating in the opposite direction and bringing the drive roll (7) out of driving frictional contact with the vertical guide. 1 0. A driving mechanism as defined in claim 9, characterised in that one end of the spring (15) is attached to the wall structure of the bracket (3 a) and the other end to an arm (16) articulated in the wall structure, the end of the arm bearing against the vertical guide (la) over the roll, and that the bracket (3a) comprises a lever (4) by means of which the bracket (3 a) is rotated against the spring force in order to detach the drive roll (7) from the vertical guide (la).

Inventors: REUNANEN JUHA, REUNANEN, JUHA
Applicants: REUMI OY, REUNANEN JUHA, REUNANEN, JUHA
Application year: 1999
Main classification: G03B15
IPC codes: A63J1, G03B15, G03B21