Patent Publication Number: US-6210023-B1

Title: Anti-noise system for a moving object

Description:
This invention relates to anti-noise connections in a motor-driven assembly, and more particularly to a combination of anti-noise elements which quiet the operation of such an assembly. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     The entertainment industry requires that lights and light modifying elements such as color changers be moved. Motors and other moving elements, however, are inherent sources of noise. The inventors of the present invention realized that silent operation is highly desirable so that an audience watching a theater production will not be disturbed. 
     However, there is a trade-off between the speed of movement of various elements and the amount of noise that they produce. Belts and pulleys can be just as noisy as gears, depending on the speed and quality. Belts and pulleys are very noisy when running fast. The first stage of a reduction train runs at speeds which are typically above 1500 rpm. This high speed operation invariably produces noise. At speeds below 1500 rpm, belt and pulley systems become much quieter. This is especially true when noise-reducing mechanisms, such as special tooth-cutting methods, are used. The belt and pulley uses a rubber belt to transmit the force from the driving pulley to the driven pulley. The belt and pulley inherently has low noise transmission and noise vibration. The damping effect of the belt in essence minimizes the transmission of noise and vibration. 
     Gears, on the other hand, transmit noise directly from the driving gear to the driven gear due to direct contact between the teeth. 
     The inventors recognized that belts do a very good job of preventing noise transmission so long as they are going slow. The inventors realized, therefore, that a belt in the final stage of the reduction train would help quiet the system. The high speed portion will inherently have noise therein. Since both gears and pulleys will cause noise, the inventors recognized that the quietest solution for the high speed portion is to use small plastic gears with small teeth. This portion will inherently have noise therein. 
     It is an object of the present invention to isolate this noise and prevent it from traveling through the rest of the system. 
     The inventors of the present invention noticed that such noise, although often masked by the sounds of the theater production, can prove very bothersome to the user. In order to obviate this problem, the inventors determined that a certain combination of elements minimizes the noise from such systems. 
     A preferred embodiment uses a connection between an output shaft of a motor and a pulley which is formed using an anti-noise element combination. The pulley is then connected via a belt to a driven shaft. One element of the anti-noise element combination includes a flexible coupling system which has inner surfaces which are substantially the same shape as the outer surface of the driving shafts. Typically these driving shafts are cylindrical. The flexible coupling has elements allowing tightening of these surfaces around the driving shaft. When a specific end of the coupling is tightened, it contracts in size around the shaft, thus tightly gripping the shaft. 
     Many different kinds of couplings are used. The most preferably used one includes a plurality of circumferential cuts through the middle portion. These cuts, and the material of the coupling, contribute to the ability of the flex coupling to flex in directions which are perpendicular to the axial direction. This has the advantage of minimizing the amount of direct physical noise across the coupling. Rubber grommets are preferably used to minimize driving motor and the plates supporting the pulley system. 
     The inventors also recognized that misalignment of shafts tends to cause even more noise, e.g. “creaks” and “groans”. Another aspect addresses these problems adaptively adjusting a position of the output axis in a way that minimizes these problems. 
     Another aspect of the invention relates to tensioning an endless loop element which drives a light modifying element of a stage lighting device. The device has a light source for emitting light and a light modifying element for modifying such light. The light modifying element is coupled to a driven element which is rotationally coupled to a structural member so as to be rotatable about a first axis. The device has a noise-producing motor assembly with an output shaft. A driving element is coupled to the output shaft to be rotationally driven by the output shaft about a second axis. The driving element is coupled to the driven element by an endless loop element so as to rotationally drive the driven element about the first axis. 
     A vibration-isolating mounting structure couples a motor assembly to the structural member and includes surfaces which vibrationally isolate the motor assembly from the structural member to attenuate vibration transferred from the motor assembly to the structural member. The mounting structure is pivotally coupled to the structural member with a pivotal range of motion about a pivot axis which is substantially parallel to the first axis. A tensioner couples the structural member to the mounting structure to bias the mounting structure in a first direction about the pivot axis so as to maintain a tension in the endless loop element. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other aspects of the invention will now be described in detail with reference to the accompanying drawings, wherein: 
     FIG. 1 is an exploded perspective view of a motor using the anti-noise elements of the present invention. 
     FIG. 2 is a cross-sectional view of an assembled anti-noise assembly according to a first embodiment of this invention. 
     FIG. 3 is a cross-sectional view of an assembled anti-noise assembly according to a second embodiment of this invention. 
     FIG. 4 is a partial front view of a lighting system having an anti-noise assembly according to a third embodiment of this invention. 
     FIG. 5 is a partial cross-sectional view of the system of FIG.  4 . 
     FIG. 6 is a perspective view of a damper assembly according to another embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a preferred embodiment of a motor assembly for use with the anti-noise elements of this invention. 
     FIG. 1 shows DC motor  10  having a power input  12  and a serial control input  14 . Control input  14  is designed to attach to a mating plug from a control panel, computer, or similar controlling unit. The motor is controlled by applying power through line  12 , and the resulting motion is monitored via encoder output  14 . 
     The rotational output of motor  10  has a high speed, since this is the initial stage of the motor. As described above, the gears are preferably high quality plastic small gears which use well-known techniques to minimize the amount of noise they produce. Since, however, these gears run at high speed, they inherently produce noise. 
     Gearbox  16  reduces the speed of rotation as desired so that output shaft  18  produces the speed-reduced rotation. 
     Mounting plate  20  is attached directly to a surface  19  of the Gearbox  16 . 
     The motor assembly is to be attached to another object, here bracket  28 . The motor assembly, however, is noisy, and the pulley in the bracket  28  is not noisy. 
     Rubber grommets  31  are provided in holes  30  in attachment bracket  28  to prevent any metal to metal transmission between the attachment plate  20  and the bracket  28 . FIG. 2 shows the arrangement of these grommets in detail. The grommet  31  fills a hole  30 . A screw  26  goes through the hole within the grommet  31 . The screw  26  is held in place by nut  32 . This hence holds the motor assembly to the bracket  28 , and effectively prevents metal-to-metal contact between the plate  20  and bracket  28 . 
     Bracket  28  preferably includes extending legs  34  including holes allowing attachment to another object tabs  36 . Each tab  36  includes a mounting aperture  38  formed therein. Only the low noise side of the motor assembly is connected to the bracket  28 . The high speed motor is left “hanging”; held by the screws and grommets. The high speed motor can hence be wiggled and moved relative to the frame on which it is mounted. This further facilitates isolating the noise produced by this high speed motor. 
     Stand-offs  40  are attached to a top surface of attachment bracket  28 . Each stand-off top surface includes threaded aperture  42  to receive a bolt which holds the pulley  48  in place. 
     Lower bearing  44 , flexible coupling  46  and pulley  48  all cooperate to transmit power from output shaft  18  to a belt and thereby to a shaft to be driven by the assembly. This shaft can be used to drive a color changer, pan and/or tilt functions in a moving light, or any in other device where minimization of noise is important. 
     Lower bearing  44  is held within a receiving opening  56  in attachment bracket  28 . Lower bearing  44  includes inner surfaces defining an area within which pulley  48  is rotated. These inner surfaces are appropriately shaped to facilitate rotational movement of the pulley  48 . 
     Pulley  48  typically includes a belt wound therearound to provide power to a driven element. Since this pulley is downstream of the speed reduction carried out by the gear mechanism in Gearbox  16 , however, the pulley operation can be relatively quiet. 
     According to the present embodiment, a noise-isolating element  46  couples between the shaft  18  from the Gearbox and the shaft  104  from the pulley. This noise-isolating element, according to this embodiment, needs to be an element which provides some measure of sound isolation between the two elements. The preferred mode uses the flexible coupling described above. This is an element often used for coupling mis-matched shafts. Other similar elements, however, can alternately be used. These include other kinds of flexible coupling elements, or any means which connects rotating elements while attenuating the sound therefrom. For example, the noise-isolating element could be embodied by a bellows, a coiled spring or other elements. The flexible coupling elements described herein are advantageous in their constant velocity and high strength. 
     One example of a suitable flexible coupling is described in U.S. Pat. No. 3,068,668, the contents of which are hereby incorporated by reference. 
     The flexible coupling includes a plurality of circumferential cuts which allow the flexing of the coupling. These circumferential cuts  66  allow the top portion of flexible coupling  46  to flex relative to bottom portion so that the solid top portion and the solid bottom portion need not be parallel to each other. Flexing of the coupling  46  also permits the bottom and top portions to become slightly relatively displaced laterally from each other and longitudinally toward and away from each other. This operation compensates any mismatches due to irregularities or eccentricities of output shaft  18  and drive shaft  104 . In addition to attenuating lateral, longitudinal and angular vibration, the flexible coupling may attenuate slight rotational vibration associated with fluctuations in the speed of the motor, lash in the gearbox, and the like. 
     Circumferential cuts  66  may be either helically formed in the flexible coupling  46  or may be individual circumferential rings. There must be some locations where the cuts do not extend through the entire diameter, to prevent one portion of the coupling from separating from the other. In either case, circumferential cuts  66  may be formed when the flexible coupling  46  is initially injection molded, or may be formed afterwards by appropriate and well-known machining methods. 
     Flexible coupling  46  may be formed of metal, or of a flexible material such as rubber or other appropriate resilient, bendable material. Alternatively, flexible coupling  46  may be formed of spring steel or other metal molded within rubber. Flexible coupling  46  is preferably integrally molded with top and bottom solid portions  62  and  64 , but these solid portions may be individually manufactured and later attached to the intermediate flexible portion containing the circumferential cuts  66 . Flexible coupling  46  is preferably pressure molded, but may be formed according to other appropriate manufacturing techniques, well known in the art. 
     FIGS. 2 and 3 show more clearly the construction of this invention when assembled. FIG. 2 shows a first embodiment in which the shaft and flexible coupling are held within the hollow pulley  48 . The second embodiment of FIG. 3 has a solid pulley  48 , and the coupling is hence outside the boundaries of the shaft. 
     Output shaft  18  is connected to the bottom surface of flexible coupling  46  which also holds output shaft  104 . Output shaft  104  holds pulley  48  which is supported in bearing  44 . In this manner, rotation of the output shaft of the high speed motor  10  is transmitted via flexible coupling to shaft  104  and thus to pulley  48 . A belt disposed around pulley  48  thereby transmits power from the motor to a shaft to be driven. 
     Pulley  48  is held in place by a retaining assembly comprising standoffs  40  and top plate  41 . 
     In operation, the motor  10  is powered by power source through input  12  and monitored via encoder output  14 . Upon input of power through input  12 , the motor rotates, thereby rotating the output shaft  18  according to the appropriate ratio of Gearbox  16 . 
     Rotational motion of the output shaft  18  causes rotation of the flexible coupling  46  which transfers the rotational motion to the shaft  104  and thereby to pulley  48 . 
     While this flexible coupling  46  has been described as joining a motor shaft with a pulley shaft, it should be clear that this flexible coupling system may also be used to couple a shaft and a pulley shaft at a distance remote from a motor. 
     FIGS. 4 and 5 illustrate a lighting system  100  incorporating another embodiment. The system  100  includes a structural member such as an equipment chassis  102 . A light source  105  which may comprise one or more bulbs of one or more types is carried by the chassis. A light modifying element such as a movable color filtering element  106  is placed in front of the source to alter a beam of light emitted by the source. The element  106  is carried by the chassis  102  for rotation about the central axis  200  of the element  106 . In the illustrated embodiment, the element  106  is carried by a central shaft  108  which is held by a bearing  110  secured in an aperture in the chassis  102 . A pulley  112  is secured concentrically to the shaft  108  and thus to the element  106 . 
     A drive system  120  is also carried by the chassis  102 . The drive system  120  includes a motor  122  and a gearbox  124  which may be similar to the motor  10  and gearbox  16  of the embodiment of FIG. 1. A mounting plate  126  may be secured to the gearbox and motor in similar fashion as mounting plate  20  is to gearbox  16  and motor  10 . As shown in FIG. 4, and in further detail in FIG. 5, the motor and gearbox are mounted on the chassis  102  by a mounting structure including three stand-off assemblies  128 A- 128 C which extend from the mounting plate  126 , through the chassis  102  and to a top plate  130 . At its end proximate the motor and gearbox (hereinafter the “proximal end”) each stand-off assembly  128 A- 128 C includes a rubber grommet  132  provided in a hole  134  in the mounting plate  126 . A screw  136  extends through a central hole or channel in the grommet and is threaded into a proximal end of a first stand-off  138  having a threaded longitudinal aperture to accommodate and engage the screw. A spool  140  is sandwiched between a distal end of stand-off  138  and a proximal end of a second stand-off  142 . The distal end of the second stand-off  142  contacts the top plate  130 . A second screw  144  extends proximally through a hole in the top plate, through the second stand-off  142 , through the spool  140  and into the first stand-off  138 . Engagement of the slot attachment  144  of each stand-off assembly  128 A- 128 C establish the top plate, first and second stand-offs  138  and  142  and spools  140  as a rigid unit. The spools  140  of the respective stand-off assemblies  128 A- 128 B are accommodated by respective apertures  150 A- 150 C in the chassis  102 . The aperture  150 A (FIG. 5) is a circular hole, closely accommodating the spool and substantially allowing only rotation of the spool and stand-off assembly  128 A about a pivot axis  202 . As shown in FIG. 4, the apertures  150 B and  150 C are formed as slots centered about the axis  202 . The spools  140  of stand-off assemblies  128 B and  128 C slide within the associated slots  150 B and  150 C so that the drive system may pivot about the axis  202  in pivotal motion constrained by engagement of the spools with the ends of the associated slots. 
     As shown in FIG. 5, an output drive shaft  156  extends distally from the gearbox  124 . A flexible coupling  158  which may be similar to flexible coupling  46  of FIG. 1 is connected at its proximal end to the distal end of the shaft  156  and at its distal end to the proximal end of a pulley shaft  160 . The shaft  160  extends through an aperture in the chassis and securely carries a drive pulley  162 . The shaft  160  extends through the top plate  130  and is rotatably coupled to the top plate  130  by a bearing  164 . Optionally, an intermediate reinforcing plate may connect the stand-off assemblies. Such intermediate reinforcing plate may be positioned on either side of the chassis  102 . For example, it may be positioned between the chassis  102  and the pulley  162 . Such a plate may carry a bearing engaging the shaft  160  to provide complimentary support to that provided by the bearing  164 . A belt  170  forms an endless loop encircling the pulleys  162  and  112  to transmit torque and rotation therebetween so as to allow the pulley  162  to drive the pulley  112  and thus drive the element  106 . 
     A tensioning mechanism maintains tension in the belt  170 . The tensioning mechanism includes a bias producing device in the form of a coil spring  180  which biases the drive system  120  in a first direction, here clockwise as shown in FIG. 4, about the axis  202 . The spring  180  is secured to a post  182  extending from the chassis  102  at one end. At its other end, the spring is secured to the second stand-off  142  of the stand-off assembly  128 B. The spring  180  is under tension to draw the stand-off assembly  128 B toward the post  182 . 
     It can thus be seen the combination of the grommets  132  and the flexible coupling  158  effectively isolate the chassis  102  and pulley  162  from noise-producing vibration of the motor  122  and gearbox  124 . 
     To describe this in further detail, an important advantage of the present system is the way in which the belt is automatically tightened. Previous self belt tightening systems have this type have been known. However, those previous systems often actually tilted the axis of one pulley relative to another. The inventors found that this tilting tends to cause creaks and groans, thereby adding to an amount of noise which is produced by the resultant system. The system of the present invention, in contrast, automatically tightens the belt in a way that forces that the axis of the adjusted pulley to remain in the same axis at all times. 
     Returning to FIG. 4, a spring element  180  tensions the device so that a predetermined amount of tension is also placed on the belt  170 . The device is attached at stand-off assemblies  128 A-C. Stand-off assemblies  128 A and  128 B each include a connecting element  500  within oversized slots  150 B and  150 C. The connecting elements  500  can slide within the slots  150 B,  150 C, allowing the overall device to pivot on the connector  202 . 
     This has the effect of tightening the belt while maintaining the axis of the driving output  204  substantially parallel to the axis of pulley  200 . 
     As explained above, this preferably done by using grommets  132  which have some extra space allowing the grommet  132  to slide within its connection point. 
     An alternative embodiment carries out automatic belt tensioning using a damper assembly with a tensioner spring. The embodiment is shown in FIG.  6 . The belt  600  is contacted by a tensioning assembly  602 . The tensioning assembly includes a one-way rotary damper  604  which can rotate in the direction shown by arrow  606 . One-way rotary damper  604  is damped in one direction but is free in the other direction. One-way rotary damper  604  is also fixed to the chassis  608  via attachment mechanism  610 . 
     Attached to the end of the one-way rotary damper  604  is an idler arm  612  which holds an idler  614  at one end thereof. The idler spins freely, to allow the belt to move across it. The other end of idler arm  612  includes a spring hole  614  with an attached spring  616 . The other end of spring  616  is also anchored to the chassis  608 . The strength of the tensioner spring  616  controls the amount of tension which is placed on the belt  600 . Tensioner spring  616  biases more tension into the belt  600 , in the direction  620 , representing the free rotation direction of the damper. In the opposite direction, the movement is damped, and hence oscillations on the belt will not cause substantial movement in the direction  630 . 
     The result is that the belt is tensioned constantly by an amount set by the spring  616 . Different strengths of springs can be used for different amounts of tensioning. Alternately, some type of variable spring, such as a spring with a turn buckle could be used. 
     Although this invention has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. 
     For example, the flexible coupling could be replaced as described above. The invention is not limited to the gears and belt drives that are mentioned herein; instead any kind of drive system could be used. The actual mounting techniques could also be replaced by any other standard technique. Additional levels of isolation may be provided such as by resiliently mounting the light modifying element to the chassis. Other modifications are contemplated.