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: 
FIELD OF THE INVENTION 
   The invention is in the field of security bars for doors. 
   BACKGROUND OF THE INVENTION AND DESCRIPTION OF RELATED ART 
   In light of the current national concern over terrorism and mass shootings in schools and other institutional settings, a relatively standardized procedure for responding to a security threat in a school building has been developed: the “lockdown”, in which teachers essentially lock themselves and their students in their rooms to deter invaders and await help. 
   A problem with the lockdown procedure is that fire safety codes typically mandate the use of outward-opening doors, and the use of locks that are key-locked from outside the room and released by simply turning the doorknob from inside the room. These fire safety measures interfere with the speed and security of the lockdown procedure. The teacher must open the classroom door, step outside, and key the lock, exposing himself and the classroom to danger; a panicky student can easily unlock the door from the inside; and if the door has the typical glass window, a gunman can break the glass, reach inside, and unlock the door by turning the inside doorknob. 
   BRIEF SUMMARY OF THE INVENTION 
   According to the invention, a horizontal locking bar is provided to quickly and effectively barricade outward-opening, doorknob-operated doors from inside a room without having to open or lock the door. Externally-locked, internally-unlocked doorknobs do not compromise the security of the locking bar, even if the doorknob is left unlocked during the lockdown procedure. “Doorknob” as used herein includes both round knobs and rotating, lever-type handles, and the inventive locking bar is suitable for use with both types. 
   When placed in its barricade position, the locking bar spans the doorway inside the room, with doorframe-engaging ends that engage the vertical sides of the doorframe in a rotation-preventing manner. The doorframe-engaging ends can be shaped to engage both protruding and recessed doorframes. 
   The locking bar has a doorknob clamping mechanism with a doorknob-engaging platform and a clamping member movable from a storage position on the platform to a doorknob-clamping position securing the doorknob-engaging platform (and thus the bar as a whole) to the inner doorknob. A lock is optionally (but preferably) provided for locking the clamp in the doorknob-clamping position. The platform can be an integral part of the bar, or separately formed and attached to the bar, depending on the preferred method of manufacture. 
   The doorknob-engaging platform initially rests on an upper part of the doorknob, preferably for hands-free support of the non-rotating bar while the clamping member is engaged provided the doorknob provides a sufficient rest surface and the bar is balanced accordingly. The platform optionally engages the doorknob in a manner that axially secures the doorknob to the bar for a temporary barricade while the clamping member is being engaged. In a preferred form for round doorknobs, the platform has a cutout or recess sized and shaped to vertically mate with and axially secure an upper portion of the doorknob. 
   The clamping member in one form is a generally U-shaped member, slidably mounted or hinged on the platform to be interposed between the door and the knob to vertically (and preferably also axially) clamp the doorknob-engaging platform to the doorknob, i.e. preventing the bar from being lifted vertically off the doorknob and preventing the doorknob from being axially disengaged (pulled away from) from the bar. 
   In one embodiment the clamping member is rigid; in another embodiment the clamping member is flexible. In a preferred form that works with both lever-type and round doorknobs, the clamping member is a rigid J-shaped member that swivels from its storage position before sliding upward to clamp the knob. 
   The locking means for the clamping member can be manually operated by the person installing the locking bar, or can be designed to engage automatically and to be released by remote signal. The clamping member and/or the locking means can be reusable or disposable. 
   The doorknob-engaging platform can be adjustable axially toward and away from the door, and/or longitudinally along the bar. The bar can also be made reversible, for use on both rightward opening and leftward opening doors. 
   While the horizontal bar portion of the locking bar is preferably a solid, non-adjustable piece, it can optionally be made adjustable in length to fit different doorframe widths. 
   These and other features and advantages of the invention will become apparent from the detailed description below, in light of the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view, from inside a room, of a partially open, outward-opening door with an external key lock, and the barricade bar of the present invention shown prior to applying it to the door. 
       FIG. 2  is similar to  FIG. 1 , but with the door closed, and the barricade bar shown pre-positioned on the doorframe above the inner doorknob in solid lines, and shown lowered into initial engagement with the doorknob in phantom lines. 
       FIG. 3  is a detailed perspective view of the clamping mechanism of  FIG. 2  in its initial engagement with the inner doorknob. 
       FIG. 4  is a perspective view of the barricade bar of  FIG. 1 , with the clamping mechanism fully engaged with the inner doorknob and locked in place. 
       FIG. 4A  is a detailed perspective view of the fully engaged and locked clamping mechanism of  FIG. 4 . 
       FIG. 5  is a front elevation view showing an alternate, automatically engaged and remotely released lock for locking the clamping mechanism to the doorknob. 
       FIG. 6  is a front elevation view similar to  FIG. 5 , but with an alternate form of clamping member using a flexible cable. 
       FIG. 7  is a plan view of the doorframe and the installed, locked barricade bar of  FIG. 1 , illustrating an optional length adjustment for the bar. 
       FIG. 7A  is a plan view similar to  FIG. 7 , but illustrating an optional position adjustment for the doorknob-engaging platform. 
       FIG. 8  is a side elevation view showing a first alternate embodiment of the doorknob-engaging platform. 
       FIG. 9  is a perspective view, similar to  FIG. 3 , but showing a second alternate embodiment of the doorknob-engaging platform, in use with a lever-handle type doorknob. 
       FIGS. 10A-10C  are front elevation views, similar to  FIG. 5 , showing alternate embodiments of U-shaped clamping members. 
       FIG. 11  is a perspective view of an alternate embodiment of a locking bar according to the invention, in use with a recessed doorframe. 
       FIGS. 12A-12B  are perspective views of alternate embodiments of a locking bar according to the invention, in which the bar engages only one side of the doorframe. 
       FIG. 13  is a front elevation view of a hinged embodiment of the clamping member. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring first to  FIG. 1 , the invention is illustrated in a preferred example from the perspective of a school classroom  10 , with an outward-opening door  12  separating the room from outer hallway  14 . Door  12  is mounted in a typical doorframe  18  with protruding vertical sides  18   a . Door  12  has a doorknob  24 , with an outer doorknob (not shown) having an external lock operated by a key. The inner doorknob  24  is without locking features. Door  12  can only be locked via the lock in the outer knob, and this requires someone in room  10  with a key to first open the door when a lockdown is initiated. Once the locked door is pulled closed ( FIG. 2 ), the door is normally unlocked by simply turning inner knob  24 , in known fashion. 
   In the case of a violent intruder, possibilities for gaining access to classroom  10  include interrupting the locking procedure while the door  12  is still open; inducing someone inside to unlock the door via inner knob  24 ; obtaining a key by force or fraud (or using a key accidentally left in the lock in the outer knob); or, if door  12  is provided with a window such as  12   a , either built into the door as shown or in the wall next to it, breaking the window and reaching through to operate inner knob  24 . The present invention addresses all of these potential weaknesses in the typical lockdown procedure with a barricade bar  30  that locks the inner knob  24  to the doorframe  18 . 
     FIGS. 1 through 4  illustrate a preferred example of barricade bar  30 .  FIG. 1  shows barricade bar  30  being applied to doorframe  18  by orienting the bar horizontally and pushing the bar  30  axially against the doorframe (as shown by the projection lines and arrow in  FIG. 1 ) to pre-position the bar above the inner doorknob  24 . Barricade bar  30  is portable, with a length approximately equal to the width of the doorframe, and so can be easily stored in a corner of the classroom, in a closet, on a wall bracket, or on a bracket concealed under a teacher&#39;s desk. Barricade bar  30  has doorframe-engaging ends  32 , shaped at  34  to allow the bar  30  to fit over and engage the doorframe sides  18   a  (including any trim over or integral with the frame) in a non-rotating manner. It will be understood by those skilled in the art that the bar&#39;s ends  32  can be adapted to fit different types of doorframes, whether the vertical sides of the doorframe protrude from the surrounding doorway (best shown in  FIGS. 7 and 7A ), or are recessed within the doorway (shown in  FIG. 11  at reference numeral  118   a ), provided that bar  30  spans the doorway, i.e. axially engages at least one (and preferably both) of the sides of the doorframe in a non-rotating manner when engaged with the doorknob to prevent the bar from being pulled outwardly through the doorway. 
   Barricade bar  30  can be made from many different materials, including wood and plastics, but metals such as steel and aluminum are preferable. It will be understood by those skilled in the art that although a generally flat, rectangular bar is illustrated and preferred, the term “bar” is not intended to exclude other shapes and cross-sections, such as bars with rounded cross-sections or the thicker, more block- or plate-like “bars” shown in  FIGS. 12A and 12B . 
     FIG. 2  shows barricade bar  30  pre-positioned on the doorframe, with ends  32  engaged with the vertical sides  18   a  of the doorframe above inner doorknob  24 , and with a clamping member  40  in a storage position to one side of the doorknob  24 . Ends  32  fit over and engage the doorframe sides  18   a  in a manner that prevents bar  30  from rotating in the vertical plane out of its horizontal, doorframe-spanning position, and that allows bar  30  to be guided down in sliding fashion along sides  18   a  onto inner doorknob  24 , as shown by the arrow in  FIG. 2 . While there are many possible ways to form ends  32 , recessed channels, lips, or half channels such as  34  approximating the contour of the doorframe, and/or flanges such as  34   a  extending inwardly toward the wall or door, are preferred for initially guiding the ends of the bar  30  onto the doorframe  18  and for preventing rotation of the bar on the doorframe once engaged. 
     FIG. 2  shows barricade bar  30  initially engaged with inner doorknob  24  in phantom lines after sliding bar  30  down along the doorframe.  FIG. 3  is a close-up view of the clamping member  40  moved to a pre-clamping position aligned with doorknob  24 . Clamping member  40  is part of a clamping mechanism  36  that also includes a doorknob-engaging platform  38  located between the ends of the bar, platform  38  extending inwardly toward and aligned over the inner doorknob  24 . The generally U-shaped clamping member  40  (shown in a preferred “J” configuration) is slidably mounted for vertical movement in the platform  38 , and normally rests in a “down” storage position as shown in  FIGS. 2 and 3  that allows platform  38  to be initially engaged with the doorknob  24 . 
   In the illustrated embodiment of  FIGS. 1-3 , platform  38  is formed as a block or plate attached to or integrally formed with bar  30 . Platform  38  has a recess, slot, or cutout  39 , in the illustrated embodiment a blind semi-circular recess (best shown in  FIG. 3 ) opening onto the platform&#39;s lower surface  38   a . The recess  39  is sized and shaped to engage the upper half of inner doorknob  24  above stem  24   a . Accordingly, as barricade bar  30  slides down the doorframe, recess  39  drops onto and mates with the upper portion of doorknob  24 , temporarily holding the non-rotating bar  30  in place and freeing the user&#39;s hands to operate the clamping mechanism. Because the inner wall or flange  39   a  of recess  39  is interposed between the knob and the door, platform  38  not only vertically supports bar  30  on the doorknob, but also axially connects the doorknob  24  to bar  30  for a temporary barricade that resists the door being pulled open. 
   The length of bar  30 , the shape of its doorframe-engaging ends  32 , and the location and dimensions of clamping mechanism  36  can be manufactured to fit a specific door/frame/knob combination. However, because doorframes can vary, and because doorknob styles and sizes can also vary, the interfaces between doorframe  18 , bar  30 , and doorknob  24  can vary; bar  30  can be adjustable in length; and platform  38  can be attached to bar  30  in removable and/or adjustable fashion. For example, the platform  38  can be connected to bar  30  with bolts ( FIG. 7A ) extending from the front face of bar  30  through the bar and into threaded bores in the platform  38 . If the size and/or shape of doorknob-engaging recess  39  does not properly fit the inner doorknob  24 , or if the size or shape of platform  38  or recess  39  does not match the doorknob, platform  38  can be moved to a different location on the bar  30  in better alignment with the doorknob, or it can be detached and a different platform can be substituted. 
     FIG. 3  illustrates clamping member  40  as a generally U-shaped (more particularly a J-shaped) rigid cylindrical bar, made from a high quality hardened steel. Clamping member  40  is slidably mounted for vertical movement on platform  38 , with its two legs  40   a  and  40   b  sliding in corresponding vertical bores or holes  38   b  and  38   c  formed in the platform. The longer leg  40   a  of the “J” is slidably trapped in platform  38  by a stop member  40   c  at its upper end, for example a nut or disc, so that clamping member  40  is retained in the platform  38  in its “down” position when the barricade bar  30  is in storage and while the bar  30  is being deployed. The shorter leg  40   b  of the J-shaped clamping member preferably ends below platform  38  and bar  30  when in the “down” position shown in  FIG. 3 , so that it can be swiveled from the doorframe-engaging position shown in  FIG. 2  to the pre-clamping position of  FIG. 3 . 
   It will be understood that the term “U-shaped” as applied to clamping member  40  is meant to include any shape extending below platform  38  to form a loop capable of being substantially closed around the doorknob stem to trap the doorknob below the platform, whether the loop is rounded or squared, and includes the preferred J-shape shown in  FIGS. 1-4 . It will also be understood that reference to platform body  38  as a block or plate is not intended to limit it strictly to a particular shape, since different shapes or thicknesses will be suitable as long as the platform  38  has sufficient strength and size to engage or at least overlie the upper part of the doorknob  24 , and to provide a secure platform for clamping member  40 . For J-shaped clamping members, it is helpful to lengthen the bores in which the clamping member slides up and down in the platform plate, in order to reduce the tendency of the long leg  40   a  of the clamping member to cock-up or bind and stick in bore  38   c  before the shorter leg  40   b  arrives in bore  38   b.    
     FIGS. 4 and 4A  show clamping mechanism  36  fully engaged with doorknob  24 . While platform  38  rests on and temporarily holds the upper half of doorknob  24 , clamping member  40  is pushed or pulled upwardly from its pre-clamping position ( FIG. 3 ) to its clamping position ( FIGS. 4 and 4A ), so that short leg  40   b  rides up into the matching bore  38   b  in platform  38 , and so that its loop or bight  40   d  rides up behind the lower half of doorknob  24  underneath doorknob stem  24   a , between the knob and the door. It is preferred that the loop or bight  40   d  engage the inner face of the doorknob  24  in a tight wedge- or cam-fit in this raised position (see  FIG. 8 ), in order to generate forces that tend to further press the ends of bar  30  against the doorframe, and to prevent any movement of the door once clamped. The J-shaped clamping member  40  accordingly can no longer swivel out of engagement with the doorknob  24 , and bar  30  cannot be lifted vertically back up the doorframe to disengage platform  38  from doorknob  24 . Clamping member  40  is then locked in this raised, clamping position with any of a number of locking means, in the illustrated example of  FIG. 4  with a simple padlock  46  whose shackle  46   a  is inserted through a hole  41  formed through leg  40   a  at a location that exposes hole  41  above the upper surface of platform  38  in the clamping position. 
   Still referring to  FIG. 4 , anyone outside room  10  trying to pull door  12  open simply forces the ends  32  of bar  30  more tightly against the doorframe  18  via the inner doorknob&#39;s engagement with clamping mechanism  36 . Lock  46  on clamping member  40  prevents the bar from being unlocked and lifted off doorknob  24  by an intruder reaching through a broken glass window, or by unauthorized or frightened people inside the room. The preferred wedge fit of the clamping member against the back face of the doorknob also prevents an intruder from rattling or shaking the door back and forth to generate any impact force or gaining any leverage against the bar and clamp and doorknob. In the most preferred form, the rear edge of the platform plate  38  is a close fit against the door to further prevent leverage that could potentially break the doorknob. 
   In order to further prevent the possibility of the barricade bar being unlocked from inside the room, or by someone reaching through a broken window with a key to the padlock  46 , and to increase the speed of the bar&#39;s deployment, an alternate, automatically-engaged locking mechanism  146  is illustrated in  FIG. 5 . Automatic lock mechanism  146  includes a transverse latching member  148  mounted to move in a bore  149  in bar  30 . Transverse bore  149  opens into the vertical bore  38   b  that the short clamping member leg  40   b  enters during the clamping operation. Locking pin  148  is normally biased by a spring  150  to extend partway into vertical bore  38   b , until it is pushed back (leftward in the drawing) by the upward movement of clamping member leg  40   b , assisted for example by an angled cam surface  148   a  formed in the free end of the pin. Leg  40   b  is modified with a detent or through-hole  140   b  located to receive pin  148  when clamping member  40  is fully engaged, automatically locking the clamping member in place in a tamperproof manner. 
   Still referring to  FIG. 5 , pin  148  and spring  150  are part of a remote-controlled, solenoid-retracted unlatching mechanism  152  mounted on or in platform  38 , similar for example to those used in remote-controlled automobile door lock mechanisms. Transmitting an “all-clear” signal to locking mechanism  146  causes solenoid  152  to retract pin  148  out of engagement with clamping member  40 , against the force of the spring, allowing the clamping member to drop freely back down to its pre-clamping position, where it can be swiveled out of alignment with the doorknob to remove barricade bar  30  from the door and doorframe. The wireless unlatching signal can come from a handheld remote control in the possession of a teacher, or from security personnel clearing the building, or can be a building-wide signal transmitted from a central office. 
   It will also be understood that while a remote-control, radio-operated type release is the preferred embodiment shown schematically in  FIG. 5 , a manually-operated release is also possible, for example a key-lock or keypad of generally known type built into bar  30  or plate  38  and capable of retracting spring-loaded latching member  148  with the turn of a key or the entry of a combination. It will also be understood that the spring-loaded latching member could be built into the clamping member, for example a ball-type detent in leg  40   b , latching with a suitable recess in bore  38   b  and releasable with a shim. 
     FIG. 6  illustrates an alternate clamping member  240  with a different type of automatic locking mechanism  246 . Clamp  240  is a flexible, generally U-shaped member whose short leg  240   b  is fixed to platform  38 , for example with an end stop  240   c , and whose long leg  240   a  terminates in a pull handle  241 . In the preferred, illustrated embodiment, clamp  240  is a cut-resistant steel cable, although other flexible members could be used depending on the desired strength of the clamp. Cable clamp  240  normally hangs down in a rest position during storage, as shown in phantom. Although pull handle  241  could be designed to be inserted through bore  38   b  in platform  38  during an emergency, it is preferred that long leg  240   a  normally remain in bore  38  with pull handle  241  resting on top of the platform. The width of the loop portion  240   d  hanging below platform  38  is preferably greater than the width of the doorknob, allowing bar  30  to be engaged axially over the doorknob; the flexibility of cable  240  allows bar  30  to be engaged vertically with the doorknob as shown in  FIG. 2  by moving the loop  240   d  out of the way of the doorknob as barricade bar slides down the doorframe  18 . 
   Once pre-engaged with the doorknob (phantom lines in  FIG. 6 ), pull handle  241  is pulled upwardly, drawing the slack in loop  240   d  up through bore  38   b  until the cable engages the doorknob stem (solid lines in  FIG. 6 ). Cable clamp  240  is preferably locked in place with an automatic locking mechanism such as the one shown schematically at  146 . A one-way toothed cam  248  is biased by a spring  250  into constant contact with the cable. Cable  240  can accordingly be pulled up through platform  38  to tighten loop  240   d  against the doorknob stem, but cannot be retracted to unlock the bar  30  from the doorknob unless the cam  248  is released, for example with a solenoid unlatching mechanism  252  operated by a remote control signal as described above, or with a key, or both. 
     FIG. 7  shows a modified barricade bar  130  whose length can be adjusted to fit different doorframes. Bar  130  has two main sections,  130   a  and  130   b , joined by an adjustment bolt  131  extending through aligned bores formed in the bar sections, and with an exposed head  131   a  at one end of the bar. The bore in the longer main bar portion  130   a  is at least partially threaded so that operating the bolt  131  serves to either draw the bar sections together or force them apart, depending on the direction the bolt is rotated. One or more spacer sections  134  with matching bores are provided to insert between main bar sections  130   a  and  130   b  as needed to accommodate different doorframe widths. Once bar  130  has been lengthened or shortened to match the doorframe  18 , the bar is ready to be stored for use in an emergency. While a bolt-operated length adjustment for bar  130  is shown, it will be understood that other forms of length adjustment could be used. 
     FIG. 7A  shows a barricade bar with a modified doorknob-engaging platform  138 , in which the platform is attached to bar  30  with two adjustable bolts  138   a  extending through bar  30 , and including one or more spacers  138   b  that can be added and removed to platform  138  as needed to adjust the distance platform  138  extends toward door  12  to properly overlie and engage doorknob  24 . By placing multiple sets of holes or slots for bolts  138   a  along the length of bar  30 , the position of platform  138  along the length of bar  30  could also be adjusted, as shown in phantom. 
     FIG. 8  illustrates another modified doorknob-engaging platform  238 . Platform  238  is essentially a flat piece that merely rests on top of doorknob  24  in the pre-engaged position. If sized and balanced properly, this might still allow barricade bar  30  to temporarily stay in place on the doorframe  18  and knob  24  while the clamping member  40  is being engaged and locked, but would not prevent the door  12  from being pulled open until the clamping member is engaged. Flat platform  238  has the advantage of being compatible with most styles of doorknob. 
     FIG. 9  illustrates yet another modified doorknob-engaging platform  338 , in which a flat horizontal platform plate  338   a  is provided with a vertical, downwardly-extending flange  338   b  interposed between the rear face of the doorknob and the door. In the case of a lever type handle such as  124 , flange  338   b  is located behind the handle portion, and is preferably wide enough to be slotted at  338   c  to drop down over the doorknob stem  124   a  to extend below the handle  124  between the handle and the door. This modified platform  338  strongly resists the door being pulled open even before the clamping member  40  has been engaged and locked. The downwardly extending flange  338   b  also helps hold the bar at rest on the doorknob while any clamping member and lock are being engaged. In some cases, for the simplest application of the bar to the door, it might be sufficient to simply drop the flange-equipped bar into place without a separate clamping member and lock, for an expedient barricade. 
     FIGS. 10A through 10C  illustrate alternate U-shaped rigid clamping members  340  and  440  and  540 , trapped for vertical sliding movement in the platform plate  38 . The clamping members have vertical legs of equal length, trapped in platform plate  38  with stops such as  40   c  on their upper ends ( FIGS. 10B and 10C ), or with a bar portion  340   a  connecting the ends of the vertical legs ( FIG. 10A ). The widths or diameters of their loop portions below bar  30  are wider than the doorknob, and in the case of clamping member  540  in  FIG. 10C  the loop portion  540   d  is provided with a narrower secondary loop portion  540   e  adapted to engage the stem  124   a  for a lever style handle, while the horizontal portion  540   d  rides up behind the horizontal portion of handle  124  either flush with the bottom of the platform plate, and preferably even recessed into a channel in the platform plate, to prevent prying. Clamping members  340  and  440  and  540  accordingly remain in axial alignment with doorknob  24 , requiring them to be initially engaged with the doorknob  24  in an axial direction while in the “down” position shown in phantom lines, rather than applied in a vertically downward direction and then swiveled into clamping engagement with the doorknob as with the J-shaped swiveling member shown in  FIGS. 1-4 . Clamping member  440  in  FIG. 10B  uses a yoke  440   d  with a rounded recess  440   e  to engage the doorknob stem  24   a , rather than a rounded loop or bight portion, and the yoke can be chamfered at  440   f  on its front face to facilitate a wedge fit against the back of the doorknob. 
     FIG. 11  shows a doorway with a doorframe  118  recessed into a wall W defining the doorway, and with recessed sides  118   a  (only one side of the doorway is shown in  FIG. 11 , the opposite side being identical). Bar  30  is modified with ends  132  adapted to fit within the recessed doorway, with a relatively close fit (for example on the order of two millimeters&#39; tolerance) between the opposing sides of wall W in order to achieve a non-rotating fit in the doorway when pressed against doorframe sides  118   a  with platform plate  38 ′ resting on the doorknob  24 . The clamping mechanism can then be operated in the manner as described above. Clamping mechanism  440  is shown by way of example, but any of the clamping mechanisms described and illustrated above would work. Platform plate  38 ′ shown in  FIGS. 10B ,  10 C, and  11  is thicker than the platform plates shown in earlier Figures, in order to provide longer sliding bores for the vertical legs of the clamping member. 
     FIGS. 12A and 12B  show modified barricade bars  300  and  300 ′, applied to the doorframe and clamped in a manner similar to the bar  30  shown in earlier Figures, but shortened in length, and their doorframe-engaging ends extended in height, to engage only one side of the doorframe  118 . The clamping mechanism and operation of the “one-sided” bars  300  and  300 ′ is otherwise similar to bar  30  as described above, except that the fit of the recess or contour  334  in the doorframe-engaging end  332  should more fully match and wrap around the contour of the doorframe. This closely-contoured, wrap-around fit to the doorframe, coupled with the increase in surface area engaging the doorframe due to the extended height of the doorframe-engaging end of the bar, would better resist the leverage generated through the doorknob at the other end. It also would serve to resist rotation of the bar relative to the doorframe. 
     FIG. 12B  shows a further variation of the one-sided bar  300 , with modified bar  300 ′ having a modified doorknob-engaging platform  338 , with a downwardly-extending flange  338   b ′ having a downwardly-opening slot  338   c ′ shaped and positioned to fit over the doorknob stem, similar to the flange structure  338   b  and  338   c  in  FIG. 9 . A transverse clamping member  340 , in the illustrated example a transverse sliding pin locked with an internal detent or regular padlock such as  46 , replaces the U-shaped clamping member shown in the preceding Figures. Pin  340  slides back and forth in appropriate bores  339  formed in the flange portion  338   c ′ to vertically clamp the bar to the doorknob  24 , preventing the bar from being lifted off the doorknob. Transverse pin  340  slides underneath the doorknob stem, and is preferably sized and shaped to have a wedge fit against the back face of the knob when pushed all the way in, for the additional advantages described above in relation to the clamping members of  FIGS. 1-11 . The modified bar  300 ′ also exhibits a thickened doorknob-engaging platform  338  relative to the platform  38  in  FIG. 12A , in order to strengthen and better unify the junction of the platform  338  with the doorframe-engaging end  332 . While pin  340  is shown as being generally horizontal, it could also be set to be inserted and engaged with the underside of the doorknob at an acute angle, for example sliding into flange  338   b ′ and underneath the doorknob stem at a 45-degree angle from the upper left side of flange, allowing gravity to assist the clamping operation. 
     FIGS. 12A and 12B  show doorknob-engaging platforms  38  and  338  that form most or all of the horizontal doorframe-spanning portions of their respective “one-sided” bars  300  and  300 ′, which are significantly shorter than their “two-sided” counterparts that span the entire doorway and engage both sides of the doorframe in the earlier Figures. This makes bars  300  and  300 ′ easier to store; it also makes them well-suited to being manufactured in a single piece, for example by molding from suitable plastics, although all of the barricade bar embodiments disclosed herein are capable of having their horizontal bar portions and doorknob-engaging platform portions formed in a single piece if desired. It should also be understood that the transverse clamping pin  340  of  FIG. 12B  could be applied to the previous examples of barricade bar using a downwardly-extending flange such as  338   b , in place of the U-shaped clamping members. 
   While the clamping members illustrated above have all shown a preferred sliding adjustment on the extension plate to clamp the doorknob, other forms of clamping movement are possible. Referring to  FIG. 13 , a J-shaped clamping member such as  640  could be hinged to the underside of an extension plate  638  as shown at  640   a . The weight and balance of clamping member  640  would preferably cause it to normally hang out of alignment with doorknob  24 . The clamping member  640  would then be swung up into clamping engagement with doorknob stem  24   a  when the barricade bar has been positioned, and the free leg  640   b  of the clamping member could then be locked in place in opening  638   c  using an automatic detent  146  or a padlock or other locking mechanism. 
   It will be understood that, although the barricade bar has been described in its preferred use for an institutional lockdown procedure, it can be used to barricade similar doors in different situations. While the barricade bar has been described in connection with its primary role as a barricade to bar an intruder from entering a room or building with an outward-opening door, it might also be used to barricade someone inside a room or building with an inward-opening door, with the terms “outward-opening” and “inner” and “inside” being considered relative to the person employing the barricade bar. It will also be understood that the disclosed embodiments are representative of presently preferred forms of the invention, but are intended to be explanatory rather than limiting of the invention. Reasonable variations and modifications of the invention as disclosed in the foregoing disclosure and drawings are possible without departing from the scope of the invention. The scope of the invention is defined by the following claims.

Summary:
A security bar for quickly barricading a doorknob-operated, outward-opening door from inside a room, especially useful for fire safety doors used in schools and similar institutions. The bar spans the doorway from the knob to at least one side of the doorframe, with the ends of the bar overlying, and preferably directly engaging, the sides of the doorframe in a non-rotating fashion. The bar has a doorknob-engaging platform that engages the inner doorknob. A clamping member carried by the doorknob-engaging platform normally rests in a storage position out of the way of the doorknob while the bar is being applied to the door, but is quickly activated to clamp the doorknob to the platform. A lock is optionally engaged to lock the clamping member in place and prevent attempts to lift the bar out of engagement with the doorknob. Attempts to force the door open from the outside simply force the bar more tightly against the doorframe.