You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to downwardly accessible suspended ceiling panels. 
       PRIOR ART 
       [0002]    One type of suspended ceiling system comprises a grid and panels that rely on springs to hold the panels vertically against the underside of the grid elements. Ordinarily, springs are provided on opposite edges of the panels. Springs can be of the torsion type having a pair of arms extending from a central coil. In a free state, the arm are widely divergent so that when confined by slots or stops at the plane of the grid, the arms draw the panel upwardly against the grid. 
         [0003]    It is known to attach the springs in a manner that enables the arms to lie flat against a rear face of the panel for shipping purposes and to extend laterally outwardly from the panel. This latter orientation allows the panel to hang from the grid by the spring arms at one side for convenience when accessing the plenum above the ceiling. 
         [0004]    Generally, it has been difficult to quickly and precisely position spring mounted panels on the overlying grid with the result that the joints between the panels are often noticeably irregular. This poor registration can be the result of reliance on the suspension springs to locate a panel in the horizontal plane both laterally and longitudinally. 
       SUMMARY OF THE INVENTION 
       [0005]    The invention is embodied in a novel multi-function clip that attaches a suspension spring to the ceiling panel. The clip enables the spring to hinge through 180 degrees for shipment and for convenient access. The clip, additionally, can hold the spring at a 90 degree orientation relative to the panel to facilitate installation. Besides its role in attaching the suspension spring to the panel, the clip serves to precisely locate the panel on the grid. The locating function of the clip enables the panels to be quickly and precisely installed. As disclosed, the clips can eliminate a horizontal positioning function from the purpose of the springs. 
         [0006]    In the preferred embodiment, the clip is a one piece sheet metal stamping having a bent finger that serves as a hinge pin on which is captured a coil of the suspension spring. The finger or hinge pin is disposed between a pair of spaced stops of the clip that restrain the spread of the spring arms extending from the coil. The stops frictionally hold the spring arms in a 90 degree orientation. In this orientation, the spring is most easily grasped for alignment and insertion of the spring arms into receiving slots in the overlying grid runner by an installer or technician. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a perspective view of a rear face of a ceiling panel for a suspended ceiling; 
           [0008]      FIG. 2  is a perspective view of an area of the ceiling panel of  FIG. 1  on an enlarged scale showing a typical clip and spring assembly of the invention with arms of the spring in a plane at 90 degrees to the plane of the panel; 
           [0009]      FIG. 3  is a view similar to  FIG. 2  showing the spring arms folded onto the panel for storage and shipment; 
           [0010]      FIG. 4  is a view similar to  FIG. 2  with the spring arms folded outward as they are when a panel is suspended from one side. 
           [0011]      FIG. 5  is a view of a lower face of a flange of a cross runner for use with the panel of  FIG. 1 ; 
           [0012]      FIG. 6  is an enlarged view of a slotted portion of the flange of  FIG. 5 ; 
           [0013]      FIG. 7  is a cross-sectional view of the grid runner of  FIG. 5 ; 
           [0014]      FIG. 8  is a fragmentary perspective view, from above, of the panel installed on a grid runner; and 
           [0015]      FIG. 9  is a perspective view of the panel of  FIG. 1  hanging from one side thereof on a cross runner in a suspended ceiling to permit access to the plenum above the ceiling. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]    Referring now to the drawings, a ceiling panel  10  for a suspended ceiling has a rectangular shape which can be square or, as shown in  FIG. 1 , rectangular. Nominal sizes of the panels include 2 foot×2 foot and 2 foot×4 foot. Dimensions given in this disclosure are intended to include industry metric equivalent dimensions. 
         [0017]    The illustrated panel  10  is formed of sheet metal, typically 0.032 inch gauge aluminum, and has its four edges bent upwardly to form generally vertical sidewalls  11 . The sidewalls  11 , which give the panel  10  the configuration of a shallow pan, can be nominally 1 inch high from the front face of the panel. The sidewalls  11  can be bent slightly more than 90 degrees so that they form an included angle of, for example, 85 degrees with the plane of the panel  10 . 
         [0018]    The panel  10  is used in a conventional manner by attaching it from below to a suspended grid. The grid is typically made from main runners and cross runners, both usually of roll-formed sheet metal with the shape of an inverted tee. Cross runners or tees, nominally 2 foot or 4 foot long and optionally up to 8 foot long, are slotted to receive springs fixed to the panels. A 4 foot cross runner  12  is illustrated in  FIG. 5 . Details of slots  13 ,  14  in a flange  15  of the cross runner  12  are illustrated in  FIG. 6 . 
         [0019]    A suspension spring  17  is attached to the panel  10  with a clip  18  of the invention. The clip  18  is preferably formed as a single piece sheet metal stamping. The clip  18  can be made, for example, from 0.047 inch gauge hot dipped galvanized steel. The clip  18  has the general shape of a U-channel with a web  19 . The web  19  is generally vertically oriented and extends between lower and upper legs  21 ,  22 . The lower leg  21  of the clip  18  has a notch  23  in a middle of its distal edge. The upper opposite leg  22  is divided into longitudinally spaced zones  26 . A strap  27  is cut from respective mid-sections of the upper leg  22  and the web  19 . A distal end of the strap  27  is notched on opposite sides leaving a neck  28  dimensioned to be frictionally locked in the notch  23  on the lower leg  21 . Mutually facing edges  31  of the zones  26  are spaced a predetermined distance to properly engage an associated suspension spring  17  assembled on the strap  27 . The edges  31  are stepped at angled intermediate portions  32  to control positioning of the spring  17 . 
         [0020]    Each upper leg zone  26  has a raised tab  36 , both tabs lying in a common steeply inclined plane such that the tabs are nearly vertical. Each of the tabs  36  are beveled at  37  so that the tops of the tabs are smaller than their widths. 
         [0021]    The illustrated springs  17  are of the torsion wire type having a single coil  40  and a pair of divergent arms  41 . In the free state of the spring  17 , the arms  41  can form an angle between each other of, for example, 135 degrees. The free ends of the arms are bent slightly over 180 degrees to improve retention force and avoids potential interference with slots  14  in the cross runner flange  15 . 
         [0022]    The width of the strap  27  is sized to be received in the spring coil  40  with sufficient clearance to allow the coil to move along and pivot about the strap. The spring coil  40  is assembled on the strap  27  before the strap is finally assembled with its neck  22  in the notch  23 . The strap  27  serves as a hinge pin for the spring  17 . 
         [0023]    A panel has at least one clip and spring assembly on each of a pair of opposite edges. In the illustrated embodiment, the clips  18  are fixed to the inside of a respective sidewall  11  with pop rivet style fasteners  39 . The sidewalls  11  at the clip  18  can be notched for clearance of the spring  17  when the spring is hinged outward of the panel  10 . 
         [0024]    The cross runner  12  has two pairs of through slots  13  in its lower flange  15  at regular locations corresponding to the locations of the panel clips  18  and springs  17 . 
         [0025]    For example, the locations can be on 1 foot centers or multiples of 1 foot. The slots  13  of a pair on one side of the flange  15 , relative to a center of the cross runner  12 , represented by a web  42  ( FIG. 7 ), are slightly staggered to account for the offset of the spring arms  41  made by the coil  40 .  FIG. 3  illustrates a typical spring  17  in a retracted position where it is turned in and overlies a rear face of the panel proper; this position is useful for packaging and shipping of the panel  10 . 
         [0026]      FIGS. 1 and 2  illustrate a feature of the clip and spring assembly where the stop edges  31  frictionally retain the spring arms  41  in an upright vertical or nearly vertical plane. This function can facilitate installation of the panel  10  since it eliminates compound hand manipulation of the spring  17 . To insert the spring arms  41  in an appropriate set of slots  13 , the installer need only squeeze the arms together so that they can register with the slots. No major hinging movement of the arms from over the panel  10  or from outside the space of the panel is required. 
         [0027]    Another feature of the clip is a precise alignment function provided by the upwardly oriented tabs  36 . The tabs  36  index precisely with the cross runner edge slots  14  both longitudinally and laterally of the panel  10 . The spring arms  41  are first inserted in their respective slots  13 . The tabs  36  will index into the associated open edge grid runner slots or notches  14  under the influence of the vertical upward force developed by the associated spring arms which when disposed in the slots bias the panel upwardly towards the cross runner flange  15 . The upward spring force is effective when the panel  10  is near the desired position and is moved along the cross runner  12  to snap the tab  36  into a respective slot  14  thereby properly locating the panel  10  longitudinally on the cross runner  12 . 
         [0028]    The inclined angle, off the vertical, of the tabs  36  serves to center the panel  10  laterally with respect to the cross runners  12  on opposite sides of the panel as the springs  17  draw the clips  18  towards the cross runners. 
         [0029]      FIG. 8  illustrates a clip and spring assembly of a panel  10  precisely positioned in a final assembly with a cross runner  12 . It will be seen that the clip tabs  36  are fully received in the edge slots  14 . There is negligible longitudinal clearance in the longitudinal direction of the cross runner  12  between a tab  36  and a slot  14  and essentially no clearance in the lateral direction. The inclination of the tab  36  guides the tab into a slot  14  and the clip is proportioned to locate the tab laterally tightly against the bottom of the slot  14 . 
         [0030]    From the foregoing, it will be seen that the several clips  18  of a panel  10  are effective to precisely locate the panel both laterally and longitudinally in the horizontal plane of a ceiling grid and that this positioning is independent of the horizontal location of the respective springs  17 , it being understood that they are loosely received in the slots  13 , and on the strap  27 . 
         [0031]      FIG. 9  shows a panel  10  disengaged from a suspended grid  46  at one side of the panel to provide access to the plenum above the suspended ceiling indicated at  47 . As shown, the ability of the springs  17  to hinge outside of the footprint of the panel  10  enables the panel to hang down at the side of the space it occupies when installed on the grid  46 . This hanging position offers ready access to the plenum and a convenient and relatively safe place to temporarily store the panel  10 . 
         [0032]    It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.

Summary:
A rectangular panel for a suspended ceiling, the panel having a suspension spring with two divergent arms at each of two opposed panel edges mounted on a rear side of the panel, each spring being mounted on the panel in an arrangement permitting the arms to lie parallel to a front face of a panel, project rearwardly perpendicular to the front face and to lie outside of the panel parallel to the front face, the spring mounting arrangement enabling the spring to be maintained in the rearward orientation by a force developed by the spring with its arms confined and locator elements for registering the panel with grid members of the ceiling.