Abstract:
A convertible sign mechanism is provided which comprises a convertible sign member that is rotatable about an axis. The convertible sign member is capable of rotating at a variable velocity. A motor is operatively connected to a drive shaft, which is connected to a cam follower. The cam follower is slidably connected to a member receiving the cam follower, with the receiving member being connected to an output gear. The output gear is connected to a drive gear, which together provide a reduction ratio of at least 2:1.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a variable speed rotary drive mechanism. More specifically, the present invention includes a drive mechanism useful in operating display sign elements, such as those on prismatic displays, so as to vary the speed of rotation from a maximum velocity occurring during the changing of display surfaces to a minimum velocity occurring as the position corresponding to the display of the desired surface is approached. 
     BACKGROUND OF THE INVENTION 
     There are several known kinds of convertible signs, one type of which creates a display arrangement comprising single or multiple prisms, each of which are mounted at opposite longitudinal ends and rotatable about their longitudinal axis. in the case of multiple prisms, each prism is part of an equal sequence in a frame, the prisms residing beside each other. The sides of the prism are oriented in a permanently occurring sequence forming a number of displays corresponding to the number of side surfaces of the single prism. Such a sign necessarily includes a drive motor for synchronous rotation of the prisms via a transmission. 
     Displays of this type usually comprise triangular aluminum prisms, which rotate in an aluminum frame and show three displays in permanently recurring sequence. The prisms can be dismounted and exchanged. Due to the triangular shape of the prisms, three different views can be shown. The display arrangement can be mounted with its frame standing free, on walls or on roofs of buildings. Also, single prism signs are typically found on scoreboards in arenas or the like. 
     Known display arrangements of this type are typically driven by an electric motor, and the prisms are rotated synchronously by a gear transmission in such a manner that the sides of the respective prisms belonging to the same picture are shown simultaneously and form a display. The gear transmission ensures synchronous rotation of each prism. 
     A gear transmission, however, involves certain disadvantages. A desirable characteristic of most convertible signs is that they operate noiselessly, particularly when the displays are mounted on buildings. A gear transmission for operating noiselessly requires good lubrication. This requirement would be difficult to attend to at many sign locations, because of the need for periodic service and such signs in most cases are positioned in places of difficult access. The problem of access has created a need for mechanisms of high durability and reliability, along with the continuing requirement for accurate registration of the sign elements and the constant need to start, rotate and stop the sign display. Experience in the field has demonstrated the need to convert this inherently complex mechanical operation into one having as much reliability and simplicity as possible. 
     A recent solution to these problems is disclosed in commonly assigned U.S. Pat. No. 5,343,645, issued to Huber. There is disclosed a chain driven gear drive system, including off-center gear elements. These gear elements are rotated to translate various potential speeds to a mounting gear, on which a sign member is mounted. As a result of this structure, the sign member rotates through successive 120° turns while varying the speed of rotation from a maximum velocity occurring during the changing of display surfaces to a minimum velocity occurring as the position corresponding to the new display surface of the sign member, of the sign is approached. 
     What is needed is an alternate drive mechanism for driving display sign arrangements and other devices that require frequent start and stops. 
     SUMMARY OF THE INVENTION 
     The present invention provides an alternate variable speed rotary drive mechanism for operating display sign elements, such as those on prismatic displays, so as to vary the speed of rotation from a maximum velocity occurring during the changing of display surfaces to a minimum velocity occurring as the position corresponding to the display of the desired surface is approached. The variable speed rotary drive mechanism can also be used to drive other devices requiring frequent starts and stops, such as conveyors. 
     In one embodiment in accordance with the invention, a convertible sign mechanism is provided which comprises a convertible sign member that is rotatable about an axis. A drive means is connected to the convertible sign member for rotating the convertible sign member at a variable velocity, with the drive means operating continuously throughout the rotation of the convertible sign member. The drive means includes a motor, a drive shaft operatively connected to the motor, a cam follower operatively connected to the drive shaft, a member configured to receive the cam follower in a slidable engagement, an output gear operatively connected to the member; and a drive gear operatively connected to the output gear and to the convertible sign member. The output gear and the drive gear provide a reduction ratio of at least 2:1. 
     These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages and objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying description, in which there is described a preferred embodiment of the invention. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a perspective view of the convertible sign mechanism in accordance with the invention; 
     FIG. 2 is a side view of the of the mechanism, with the motion transmission device in a first position; 
     FIG. 3 is a schematic view of the motion transmitting device in a first position; 
     FIG. 4 is a schematic view of the motion transmitting device in a second position; 
     FIG. 5 is a schematic view of the motion transmitting device in a third position; and 
     FIG. 6 is a schematic view of the motion transmitting device in a fourth position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a convertible sign mechanism according to the principles of the invention is shown generally at  10 . The convertible sign mechanism  10  includes a multifaceted prismatic display member  12 , which can have two or three sides, but in the specific example is shown to have three-sides  14 ,  16 ,  18 . The sides  14 ,  16 ,  18  typically contain different information, and when in a multiple prismatic sign, are typically ganged or combined together with similar display members in a coordinated manner to form the desired sign. The mechanism  10  further includes a drive mechanism  20  for rotating the display member  12  about its central axis so that each side  14 ,  16 ,  18  is periodically brought into view. 
     With reference now to FIGS. 1 and 2, the drive mechanism  20  generally includes a suitable electric motor  22  having a drive shaft  24  with a pinion gear  26  fixed thereto, such that the pinion gear  26  is rotatably driven by the motor  22 . The motor  22  is typically timed by conventional timing devices or the motor can be under computer control. An endless chain  28  is disposed over the drive gear  26  and an input gear  30  that is fixed to an input shaft  32  which forms the input to a variable speed, motion transmitting device  34 . An output shaft  36  extends from the device  34  and has an output gear  38  fixed thereon so as to rotate with the output shaft  36 . A second endless chain  40  is disposed over the output gear  38  and a large diameter drive gear  42  that is fixed to a shaft  44  which is connected to the display member  12 . 
     When the motor  22  is activated, the drive shaft  24  rotates the pinion gear  24  which drives the endless chain  28 . The endless chain  28  in turn drives the input gear  30 , thereby rotating the input shaft  32 . The motion transmitting device  34  continuously varies the rotational speed input by the input shaft  32 , so that the rotational speed of the output shaft  36  and the output gear  38  are continuously varied. The rotation of the output gear  38  is transmitted by the endless chain  40  to the large diameter drive gear  42  which drives the shaft  44  thereby causing the display member  12  to rotate so as to change the side  14 ,  16 ,  18  that is viewed. 
     A concern when driving members that are periodically stopped and started, such as prismatic display members and conveyor systems which stop and start at fill stations, is that the initial start of movement from a fully stopped condition be gradual. The movement speed should eventually build up to a maximum, and then gradually decrease as the driven member starts approaching its next intended position. Applicant&#39;s have found that this gradual increase and gradual decrease of movement speed avoids the shock of abrupt starts and stops, and minimizes wear on components. 
     In order to accomplish the gradual increase and gradual decrease of the rotational speed of the display member  12 , the motion transmitting device  34  is specifically designed to convert the constant speed rotational input provided by the input shaft  32  into a smooth, cyclically varying speed, accelerating-decelerating rotational output to the output shaft  36 . 
     With reference specifically to FIG. 2, it is seen that the motion transmitting device  34  includes a pair of spaced side walls  46 ,  48 , each of which includes a bearing  50 ,  52  associated therewith for rotatably supporting the respective shafts  32 ,  36 . A cam follower arm  54  is suitably fixed to the end of the input shaft  32 , such as by a key, so as to rotate with the input shaft  32 . A follower  56 , such as a rotating bearing or a sliding bearing, is fixed to the follower arm  54  and is spaced radially of the axis of the input shaft  32 . A cam arm  58  is suitably fixed at one end thereof to the end of the output shaft  36 , such as by a key, whereby the cam arm  58  is eccentrically mounted. The cam arm  58  includes a slot  60  formed therein which extends longitudinally the length of the cam arm  58 , and the follower  56  is slideably received within the slot  60 . Thus, as the input shaft  32  rotates, the output shaft  36  rotates as a cyclically varying speed due to the cam and follower arrangement. 
     Preferably, the follower  56  is spaced from the axis of the input shaft  32  a distance slightly greater than the distance between the axes of the input and output shafts. Thus, as the input shaft  32  rotates, the cam follower arm  54  and the follower  56  rotate therewith. Rotation of the follower arm  54  and follower  56  causes the cam arm  58  and the output shaft  36  to rotate. The rotational speed of the input shaft  32  can be assumed to be constant, and therefore due to the arrangement of the device  34 , the rotational speed of the output shaft  36  will vary from a maximum when the follower arm/follower  54 ,  56  and the cam arm  58  are in the position shown in FIGS. 2 and 3, to a minimum when the follower arm/follower and cam arm are displaced 180° to the position shown in FIG.  5 . The transition between maximum and minimum rotational speeds of the output shaft  36  occurs in an extremely smooth manner due to this arrangement, such that abrupt starts and stops are avoided. 
     The variation in rotational speed occurs based upon the distance of the follower  56  from the axis of the output shaft  36 . Referring now to FIGS. 3-6, when the follower  56  is at its maximum distance from the output shaft axis, as illustrated in FIG. 3, the torque acting on the cam arm  58  is greatest since the moment arm D of the force acting on the cam arm is at its maximum. As the elements rotate to the position shown in FIG. 4, the follower  56  is moving toward the output shaft  36 , and thus the rotational speed of the output shaft  36  is continuously decreasing. When the elements reach the position shown in FIG. 5, the follower  56  has moved to its closest distance to the output shaft axis. Therefore, the torque acting on the cam arm  58  is at its minimum, since the moment arm of the force is at its minimum. As the elements rotate from the position shown in FIG. 5 to the position shown in FIG. 6, the follower  56  moves away from the output shaft  36  so that the rotational speed thereof gradually increases. 
     It is important that the follower  56  be spaced from the axis of the input shaft  32  a distance slightly greater than the distance between the axes of the input and output shafts, i.e. the axis of the follower  56 , should not coincide with the axis of the output shaft  36 . This prevents binding of the follower  56  in the cam arm  58 , which would stop rotation of the output shaft  36  and possibly damage the components. 
     Assuming that the display member  12  is initially at rest and the side  14  is currently viewable, then to view the side  16  the display member  12  must be rotated about its axis. This is accomplished by activating the motor  22 , which drives the input shaft  32  in the suitable direction. Initially, the follower  56  and cam arm  58  are in their minimum rotational speed position (FIG.  5 ). When the input shaft  32  is rotated, the follower arm  54 /follower  56  start driving the cam arm  58 , with the rotational speed gradually increasing as the follower  56  and cam arm  58  move away from the minimum speed position (FIG.  6 ). Concurrently, the display member  12  starts to gradually rotate from its stopped position. 
     Continued rotation causes the follower  56  and cam arm  58  to reach their maximum speed position (FIG.  3 ), at which point the display member  12  is being driven at its maximum speed and the side  16  is partially visible. As the follower  56  and cam arm  58  move from the maximum speed position, the speed of the display member  12  starts decreasing as the side  16  of the display member is starting to approach its fully viewed position (FIG.  4 ). When the side  16  reaches its fully viewed position, the follower  56  and cam arm  58  will be back at their minimum speed position (FIG.  6 ). To stop the display member  12  in position, one need only to deactivate the motor  22  at the minimum speed position. 
     Ideally, for a three-sided (prismatic) display member  12 , the output gear  38  and the large diameter drive gear  42  are sized to provide a 3:1 reduction ratio, such that a complete cyclic speed variation provided by the motion transmitting device  34  occurs for every 120° rotation of the display member  12 . This ensures that the display member  12  goes through the cycle of gradual speed increase, maximum speed, and gradual speed decrease to minimum speed each time a new side is to be viewed. For a two sided display member a 2:1 reduction ratio would be provided. 
     While the invention has been described herein as driving a display member, the invention could also be used to drive any member requiring frequent starts and stops, such as conveyors with containers thereon which stop and start at fill stations to fill the containers. The gradual increase and decrease of speed provided by the motion transmitting device described herein would prevent the containers on the conveyor from tipping over, with the maximum speed between starting and stopping maintaining efficient operation of the conveyor. 
     The above specification provides a complete description of the manufacture and use of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.