Abstract:
An apparatus is described which includes a frame, a video monitor display mounted to the frame, a torque shaft coupled to the frame such that rotation of the torque shaft causes the frame to pivot along a predetermined arc. The apparatus further involves engaging to the torque shaft to impart rotational motion to the torque shaft, a releasable cam follower slidably disposed on the cam shaft and a spring mounted on the cam shaft exerting a spring bias force directed toward the cam so as to cause rotational motion of the cam.

Description:
FIELD OF THE INVENTION 
     The present invention relates to video display units that can stow and display a monitor. 
     BACKGROUND 
     Entertainment and information systems aboard aircraft have been made available to passengers for their comfort. Such systems can include television monitors that display movies and other programming, including safety instructions. Monitors can be stowed in the ceiling of the passenger cabin and are typically attached to a hinge allowing for rotational deployment from a cavity in the ceiling. An electric motor typically provides the power enabling rotational deployment, including retraction of the monitor when not in use. Electrical power necessary to deploy and retract the monitors comes from that generally available to the aircraft for use by the cabin during flight. It is therefore desirable to reduce power consumption to enhance efficient usage of on board systems. 
     In an emergency situation, deployed monitors can be a significant obstacle to both movement and line of sight for passengers. As such, where the aircraft cabin loses electrical power, Federal Aviation Administration regulations require that all monitors be retracted and stowed in a specific time frame of approximately five seconds. Where monitors were of a smaller size, i.e., approximately 8.4 to 9 inches, a battery or other stored power source within the monitor could suffice to automatically retract the monitors and comply with the FAA regulations, even though this extra power source constituted a further drain on energy needed to charge and maintain potency. Furthermore, this is less feasible for larger size screens, i.e., those 15 inches and larger, which required significantly greater rotational force to be generated in order to automatically retract them in the time period required. Additionally, these larger screens, with their greater power consumption for rotational motion, benefit from a more efficient source of rotational force. Torsion springs are the most common mechanism currently used for this purpose, but are not very efficient from a systems operation standpoint. This is due to the fact that less torque is required when the monitor is deployed than stowed which is opposite of the operation of torsion springs. 
     SUMMARY 
     An apparatus is described which includes a frame, a video monitor display mounted to the frame, a torque shaft coupled to the frame such that rotation of the torque shaft causes the frame to pivot along a predetermined arc. The apparatus further involves engaging to the torque shaft to impart rotational motion to the torque shaft, a releasable cam follower slidably disposed on the cam shaft and a spring mounted on the cam shaft exerting a spring bias force directed toward the cam so as to cause rotational motion of the cam. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements and in which: 
     FIG. 1 illustrates a side perspective view of the invention showing a video display monitor in a retracted position. 
     FIG. 2 illustrates a partially exploded view of the display unit of FIG. 1 showing the cam rotational assembly of the invention. 
     FIG. 3 illustrates an exploded view of the spring cam assembly of the invention. 
     FIG. 4 shows a side perspective view of the spring cam assembly of the invention. 
     FIG. 5 shows a side view of the spring cam assembly of the invention. 
     FIG. 6 is a table showing relative forces and torques for the display monitor of the invention at particular deployment angles. 
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings more particularly by reference number, FIG. 1 shows a side perspective view of the display unit of embodiment of the present invention. Frame  10  houses the display screen  55  and components related to the video monitor (collectively identified as  11 ). Frame  10  is rotationally coupled to torque shaft  37  extending laterally across frame  10  for mounting within a cavity where the monitor will be stowed and deployed from (not pictured). Torque shaft  37  includes torque shaft gear  38  engaged to slip clutch  30  with which gear  38  meshes. Slip clutch  30  is connected to output shaft (not pictured) of electric gear motor  29 . Also attached to the output shaft is magnetic brake  88 . 
     Frame  10  and inclusive monitor can be stowed in a substantially horizontal position within a cavity within the ceiling above the seating area in the cabin. To deploy the monitor, electric gear motor  29  activates slip clutch  30  causing rotation of the meshed gear  38  mounted on torque shaft  37  so that frame  10  rotates in a pivotal arc until it reaches a substantially vertical position, perpendicular to the cabin ceiling. It may also be appreciated, that frame  10  can be deployed over an arc greater than 90 degrees, i.e., to 120 or 130 degrees, in order to accommodate the viewing angles of passengers seated below the monitors. A downsensor wheel  31  and infrared gate sensor  15  may be used to sense the position of the monitor and accordingly engage brake  88  to halt further rotation at the desired position. Other methods of sensing position known in the art may also be utilized. 
     In this regard, spring cam assembly,  28  may be mounted between torque shaft  37  and motor  29  and motor shaft (not pictured). In an alternate embodiment, spring cam assembly  28  can be mounted directly on torque shaft  37 . The degree of rotational motion may be regulated by co-rotational motion of this assembly, and especially cam  1  (pictured in FIGS.  2 - 5 ), between two points on the shaft represented by the placement of bearing  5  on the assembly inhibiting further cam rotation. Slip clutch  30  may also be constructed so as to disengage from gear  38  upon the application of a pre-determined amount of force, allowing torque shaft  37  to rotate frame  10  and inclusive monitor, upward to a stowed position. 
     FIG. 2 shows an exploded view of one embodiment of the invention. In this view the spring cam assembly  28  and its elements are more clearly viewed. Assembly  28  includes cam  1  and cam shaft  1   a  which is coupled to precision ball bearing  42  at bearing clamp  39 . In addition to the aperture for cam  1  and bearing  42 , clamp  39  includes a second aperture where motor  29  is coupled to clutch  30 . Compression spring  3 , is threaded around cam shaft  1   a . Adjusters (not pictured) maintain spring  3  centered on cam shaft  1   a . Cam follower  2  sits between cam  1  and spring  3  on cam shaft  1   a . Torque stop  7  is shown in this figure, as installed after manufacture, but is withdrawn upon installation of assembly  28  and prior to its operation. Fastening means pictured for this embodiment of the invention include screws  41  and washers  56  affixing bearing clamp  39  to motor  29  around output shaft where clutch  30  is fitted onto motor  29 . Similarly, drive end plate  36  is fitted onto torque shaft  37  and clutch  30  at apertures  72 . 
     FIG. 3 shows an exploded view of the cam assembly of one embodiment of the invention. In its operation, cam  1  and cam shaft  1   a  are mounted on and co-rotate with torque shaft  37  when frame  10  and inclusive monitor are deployed by operation of motor  29  and clutch  30  on gear  38  of torque shaft  37 . During co-rotation, cam follower  2  displaces along cam shaft  1   a  against compression spring  3  which is compressed against spring spacer  4  and thrust bearing  5 . Compression by cam follower  2  imparts substantial potential energy contained within spring  3 , biasing its force against cam follower  2 , and hence against coupled cam  1 . This potential energy and biasing force remains while frame  10  and inclusive monitor are deployed in the viewing position. 
     Brake  88  in FIGS. 1 and 2 prevents rotation of torque shaft  37  with cam follower  2  fixed thereon inhibiting relaxation of spring  3  from its compressed state. Where frame  10  and monitor are to be retracted to a stowed position, brake  88  relaxes and spring  3  exerts its bias force against cam follower  2 . Once the brake is released, spring  3  is then free to expand, in turn the cam follower exerts translated bias force on cam  1  to counter rotate the cam and, thus, counter-rotating torque shaft  37  to retract monitor and frame  10  to its horizontal or stowed position. 
     Where the biasing force of the compressed spring will thus serve to retract the monitor either alone or in conjunction with a motor, the necessary electrical usage is minimized and the monitor is more efficiently operated, while still achieving FAA standards of “breakaway” or rapid retraction in a specific time period. Enabling this biasing force is the size and strength of the spring used. It is therefore preferable that the invention utilize a spring capable of retaining significant potential energy and which can generate sufficient force to retract a 15″ or larger video monitor display. Typically, a 15″ monitor has a mass in excess of at least 3 times the mass of a 6″-8″ monitor. In this regard, a torsion spring, which is generally thinly constructed and yields only a modest bias force, is insufficient and also requires significant extra power from the motor to deploy. In contrast a compression spring, especially one which is heavy duty, and mated with a cam profile specifically designed for the application to the most efficient design, suffices. Within limits, if the spring rate is low, the cam face profile needs to be steep. If the spring rate is high, the cam face profile needs to be shallow. Given their higher stress levels, torsion springs typically also enjoy an operational life only {fraction ( 1 / 10 )} as long as a compression spring. 
     FIGS. 4 and 5 provide further illustrations of the cam assembly, including cam follower  2  which is slidably mounted on cam shaft  1   a  so as to compress a spring (not pictured) mounted thereon. Bearing  5  provides the stop point for cam  1  rotation about the longitudinal axis of cam shaft  1   a  and also provides a stop point for the lateral movement of cam follower  2  toward cam  1  when impelled by expansion of a compressed spring. 
     FIG. 6 is a table showing the torque and spring forces exerted by the monitor, cam and spring in one embodiment of the invention depending on the angle of monitor deployment. The table refers to the forces and torque necessary to stow a 15″ video monitor. As is evident, spring force required to maintain the monitor at a horizontal ceiling position, i.e. in its stowed position, is 84.7 lbs. This spring force increases to 151.4 lbs. to retract the monitor from a pivoted position 130 degrees from the horizontal. Cam face angle of rotation over this period is between 45 degrees and 5.70 degrees. Compression distance in the spring is reflected in the “total travel” portion of the tableDelta travel is the distance from one step to another. 
     Thus the figures show to retract a 15″ video monitor from a 130 degree deployment angle, 151.4 lbs. of force is required from the spring. Due to friction, the compression spring utilized imparts slightly less than this, yet is sufficient to retract the monitor to its stowed position. When the compression spring  3  is at 84.6 lbs. of force, it provides 70.0 in/lb. of torque to keep the monitor stowed. When it is at 151.4 lbs. of force, it provides 12.5 in/lb. of torque to direct the monitor stowed. If a torsion spring were used to achieve 70.0 in/lb. of torque to keep the monitor stowed, the deployed torque would be 115.8 in/lbs. 
     In the preceding detailed description, the invention is described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.