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 
     1. Field of the Invention 
     The present invention relates to a control device for closing and opening a door. More particularly, the present invention relates to mechanisms for facilitating various control operations of a door. 
     2. Description of the Relevant Art 
     Doors which close in response to a predetermined condition, such fire doors, are well known in the background art. A fire door serves as a barrier to the spread of fire, smoke or fumes through an opening or throughway in a building interior or exterior wall. Fire doors can be stored in a ceiling, wall or floor of a building, and close downwardly, sidewardly, or upwardly, respectively, to close the throughway automatically upon a sensed condition, such as excessive heat or smoke. 
     A rolling fire door is usually constructed of a plurality of interconnected fire-resistant slats, which are rolled up and stored on a rotating pipe over, under, or next to a throughway. Fire doors may also be of other designs. For example, a fire door could be a solid section or a combination of solid and rolling sections. Rolling overhead fire doors and other configurations can weigh from as little as a few hundred pounds to more than a thousand pounds. 
     Some fire doors are designed to sit open, ever vigilant for a detected fire condition. Other fire doors are operated (e.g., opened and closed) often for security and environmental reasons. These other fire doors are usually motorized, or have a manual chain hoist, in order to facilitate the opening and closing of the fire door. Most all fire doors have one or more fire links that will allow the fire door to close when excessive heat is detected. Some fire doors are also connected to smoke detector systems and alarms, so that the fire door is closed in response to excessive smoke or a fire alarm. 
     Rolling fire doors typically come in four types: manual push up; manual chain hoist; electric motor operated, non-automatically resetting; and electric motor operated, automatically resetting. Each type has inherent drawbacks associated with its design. The first three types are older designs, and have similar drawbacks. The fourth type is a newer design with different drawbacks, and therefore will be discussed separately. 
     Because a fire condition is often accompanied by a loss of electrical power, fire doors typically rely on gravity for closing, except in the case of a lightweight door, where a spring may provide a supplemental force to assist the door in closing. Side-closing, up-closing, and flat-closing fire doors also rely on springs to provide a force in the closing direction of the fire door. 
     Various mechanisms have been employed to slow and control the closing rate of a fire door, such as friction brakes, counter wound torsion springs, ratcheting systems and even a hydraulic resistance system (see U.S. Pat. No. 5,002,452). It is important to control the closing rate, since fire doors are mandated to drop at a rate of six to twenty-four inches per second, by fire codes. 
     The electric motorized types and the manual chain hoist type of fire door have a mechanism, usually a gear, held in place by a frangible fire link chain. The gear drops out of the motor gearing or chain hoist (e.g., when excessive heat is detected), so that the fire door can close independent of the motor and raising/lower mechanism. To test these types of fire doors, it is necessary to disconnect the fire link chain, so that the gear drops out. 
     A qualified door mechanic must reset the mechanism after a door is deployed in response to a fire condition or tested. Access to the mechanism is often limited, when the mechanism is buried in the ceiling, amid ducts, wires, and pipes. Therefore, testing and resetting of fire doors can be a costly endeavor. Fire codes require an annual testing of the fire doors. Further, many industrial plants require a monthly testing to meet the conditions of their insurance policies. The required testing is not only expensive, but also time consuming to oversee, manage, and reset the fire doors. 
     An additional disadvantage is that these mechanisms are prone to failure in many ways. For example, the fire door may not drop at all, resulting in major losses for insurance companies when a fire occurs. As another example, these mechanisms often do not accurately control the drop rate of the fire door, causing the fire door to crash into the floor, resulting in damage to the door, and a safety risk to anyone unlucky enough to be under the fire door when it drops. Repairing the damaged door adds to the expense associated with fire door testing, and adds to the down time associated with repairing and resetting the fire door. 
     The electric motor operated, automatically resetting type of fire door can be tested without disconnecting the fire link chain. This type of fire door relies on a centrifugal brake. This type of fire door has no overrun control, and, in fact, the motor acts like a flywheel, increasing the overrun. The motor can freewheel at 1800 RPM, and cause damage to the top slats of the fire door, especially on smaller doors, after only a few test drops. Additionally, there is no control on the drop speed of the fire door, other than the rate of close control, determined by the centrifugal brake, since the unit is designed to work in a no power condition. 
     In the electric motor operated, automatically resetting type of fire door, power must be constantly provided to the motor control mechanism in order to hold the fire door open. If power is lost to the motor control mechanism, the fire door will automatically close, even if the power outage is brief, such as during an electrical storm. If the power remains off, this type of fire door cannot be reopened for emergency personnel or emergency egress. One attempt to overcome these drawbacks has been to include an expensive battery backup system for the motor control mechanism. 
     Another drawback of the electric motor operated types of fire doors is the requirement of a constant source of AC power. AC power lines must be ran to each fire door. This is an expensive installation. For example, in a warehouse, where a 277 volt lighting system is the only power used, the cost of running additional high capacity power lines to the fire door controllers can exceed the cost of the actual fire doors themselves. The alternatives to these motor operated types of fire doors are the manual types of fire doors (the first and second types, above), which are difficult to test and reset, as noted above. 
     Both electric motor operated types of fire doors (the third and fourth types) are driven down or closed by the electric motor. Since these door controllers are designed to raise the fire doors, often when the springs are unwound, the motors have sufficient torque to cause damage to, or destroy, the door slats, if the door slats become jammed or cannot travel freely to the closed position. Often the motors will run to their bottom limit with the fire door still in the open position, while twisting, jamming, and ripping the slats in the process. This condition is also possible with other types of rolling doors, such as security grills, etc. 
     In summary, a general drawback of the background art&#39;s fire doors is that the typical fire door, once it closes, is difficult or impossible to open for emergency egress or to allow emergency personnel or equipment to enter. The electric types can be reopened, but only if power is still available, which is not always the case. If firemen cut a hole through the fire door to gain access, and the fire overruns their position, integrity is lost since the fire door is not and cannot be fully closed. Mechanical types of fire doors are prone to failure, and testing and resetting of the fire door is a costly operation because of the complexity of the mechanism, and the hindrance in gaining access to the operating mechanism. Electrical types of fire doors are easier to reset, but the installation of the equipment is expensive; continuous AC power is needed to keep the door open (or an expensive battery backup system); the drop rate control under a no-power situation is likely to result in damage to the door or persons in the vicinity; when powered down or closed, if the fire door does not run smoothly, the motor torque will do damage to the door slats; and once dropped, the fire doors cannot be easily reopened for egress or emergency personnel. 
     SUMMARY OF THE INVENTION 
     The present invention has as a primary object to improve on the mechanisms of the background art or to solve one or more of the drawbacks associated with the mechanisms of the background art. 
     It is an object of the present invention to provide a heat or smoke actuated device, including a fire link, for actuating a fire door, wherein the device can be tested without breaking or disconnecting the fire link, and wherein every closing of the fire door constitutes a testing of the device. 
     It is a further object of the present invention to provide an improved control and operating system for any type of automatically closing door, which can be opened, closed, tested, reset and controlled without the provision of any hard-wired power source. 
     It is an even further object of the present invention to provide a device, which harnesses energy generated by a closing door to control the closing of the door. 
     Moreover, it is an object of the present invention to provide a device, which harnesses energy generated by a closing door to power auxiliary operations. 
     Moreover, it is an object of the present invention to provide an improved device for controlling the closing speed of a door. 
     Moreover, it is an object of the present invention to improve the resetting characteristics of a powerless door. 
     Moreover, it is an object of the present invention to improve the operational characteristics of any motor operated door. 
     Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitative of the present invention, and wherein: 
     FIG. 1 is a perspective view of one side of a drop-type fire door, in accordance with the present invention; 
     FIG. 2 is a perspective view of the other side of the fire door of FIG. 1; 
     FIG. 3 is a cross sectional, overhead view of the drive mechanism of the fire door; 
     FIG. 4 is a cross sectional view taken along line  4 — 4  in FIG. 3; 
     FIG. 5 is a cross sectional view taken along line  5 — 5  of FIG. 3; 
     FIG. 6 is a close-up view of drop actuator mechanism of FIGS. 3 and 4; 
     FIG. 7 is an electrical schematic of a control system for the fire door; 
     FIG. 8 is a cross sectional view of a sensor strip attached to a leading edge of the fire door; and 
     FIG. 9 is an electrical schematic of an alternative control system for the fire door. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 and 2 illustrate a fire door  10 , in accordance with the present invention. FIG. 1 illustrates the fire door  10  in an open, first position, whereas FIG. 2 illustrates the fire door  10  in a closed, second position. 
     Now, the features of the fire door  10  which are commonly employed in the background art will be briefly described. The fire door  10  is provided to selectively block a throughway  12  defined inside a frame  14 . Although the throughway  12  is illustrated, as being at grade level, so that a person or vehicle could pass therethrough, the throughway  12  could also be an external window, countertop window, or any opening to be selectively blocked by the fire door  10 . Moreover, although a fire door  10  is shown and discussed, and present invention is equally applicable to any type of door, such as an open grated, security grill which closes a customer counter, a hurricane shutter for a window, a garage door, etc. Therefore, in the claims, the term “door” is intended to be broadly construed to include a broad range of structures which move in order to restrict or limit access or view through an opening, passageway, hole, or other similar location. 
     The fire door  10  is formed of a plurality of interconnected slats  13 , which are guided for vertical travel by right and left guide rails  16 ,  18 . When the fire door is in the open position, the slats  13  are rolled up onto an elongated shaft  22  (see FIGS. 3-5) and located inside a cover  20 . 
     On the right end of the cover  20  there is provided an optional spring box  23 . The spring box  23  includes an assist spring (not shown), which is keyed to the elongated shaft  22 . The assist spring can store potential energy as the fire door  10  is closed and give up the potential energy as the fire door  10  is opened, in order to assist an operator in opening the fire door  10 . Alternatively, the assist spring can store potential energy as the fire door is opened and give up the potential energy as the fire door  10  is closed, in order to assist the forces of gravity in closing the fire door  10 . Although the spring is described as being located on a side of the elongated shaft  22 , the spring could be inside of a hollow elongated shaft  22 , thereby eliminating the physical presence of the spring box  23 . 
     On the left end of the cover  20  there is provided a mechanical drive box  24 . A first chain  26  extends from a top of the mechanical drive box  24 . The first chain  26  is connected under tension to a first fire link  28 . The first fire link  28  is connected under tension to a first ceiling fixture  30  via a second chain  32 . A third chain  34  is also connected to the first fire link  28  and passes through the wall. On the other side of the wall, the third chain  34  is attached to a second fire link  36 . The second fire link  36  is attached to a second ceiling fixture  38  under tension via a fourth chain  40 . 
     The purpose of the first and second ceiling fixtures  30 ,  38  and the first and second fire links  28 ,  36  is to sense a condition indicating a fire and to provide slack to the first chain  26  entering the mechanical drive box  24 , upon the occurrence of a fire condition. For example, excessive heat, on the side of the door illustrated in FIG. 2, will melt the first fire link  28  and allow the first chain  26  to slack and partially pass into the mechanical drive box  24 . Excessive smoke, on the side of the fire door  10  illustrated in FIG. 2, or a general fire alarm, will cause the first ceiling fixture  30  to release the second chain  32 , thereby creating slack in the first chain  26  and allowing the first chain  26  to partially enter the mechanical drive box  24 . The details of such fire condition sensors can be found in the background art, such as U.S. Pat. No. 4,147,197. 
     Now, the structures of FIGS. 1 and 2, which concern the present invention will be described. A first control panel  42  is mounted on a wall adjacent to the fire door  10 . The first control panel  42  includes a first switch  44  for resetting/opening the fire door  10 , a second switch  46  for testing/closing the fire door  10 , and a first socket or electrical terminal  48  for receiving a second terminal  50  of a rechargeable battery  52 . A second control panel  54 , having a third switch  56 , a fourth switch  58 , and a third electrical terminal  60  is provided adjacent the fire door  10  on the other side of the wall, and has the same functions, respectively. To reduce costs, it would be possible to eliminate one of the first or second control panels  42 ,  54 , while retaining many of the benefits of the present invention. 
     A manual release handle  62  depends from a lower surface of the mechanical drive box  24 . Pulling the manual release handle  62  will result in a testing/closing of the fire door  10 . Optional visual indicators  64  are mounted on the walls adjacent to the fire door  10 . The visual indicators  64  light up, or strobe, when the door is tested/closed. The visual indicators  64  may include indicia, such as “fire”, “closing”, “caution”, etc. Also, optional audible indicators  66  are mounted on the walls adjacent to the fire door  10 . The audible indicators  66  beep, alarm, or play a recorded announcement, when the door is tested/closed. 
     Now, with reference to FIGS. 3-5, the components of the mechanical drive box  24  will be disclosed. A DC powered motor/generator  68  is contained therein. The motor/generator  68  rotates a first gear  70 , via a rotor  130 . The first gear  70  drives a second gear  72 , via a first chain  74 . The relative sizes of the first gear  70  and the second gear  72  result in a speed reduction. 
     The second gear  72  is attached to and rotates in unison with a first shaft  76 . A brake disk  71  of a disengageable stop or brake system  73  is attached to and rotates in unison with the first shaft  76 . A third gear  78  is also attached to and rotates in unison with the first shaft  76 . The third gear  78  drives a fourth gear  80 , via a second chain  82 . The relative sizes of the third gear  78  and the fourth gear  80  result in a further speed reduction. 
     The fourth gear  80  is attached to and rotates in unison with a second shaft  84 . A fifth gear  85  is attached to and rotates in unison with the second shaft  84 . The fifth gear  85  drives a sixth gear  86 , via a third chain  88 . The relative sizes of the fifth gear  85  and the sixth gear  86  result in a further speed reduction. The fifth gear  85  also drives a seventh gear  90  via a fourth chain  92 . 
     The sixth gear  86  is attached to and rotates in unison with the elongated shaft  22 . The interconnect slats  13  of the fire door  10  are wound or unwound about the elongated shaft  22 , as discussed above. 
     The seventh gear  90  is attached to and rotates in unison with a third shaft  94 . The third shaft  94  includes surface threading  95  along a central portion thereof A sleeve  96 , having internal threading, encircles the surface threading  95  of the third shaft  94 . The sleeve  96  includes a tab  98  fixed to an outer surface thereof The tab  98  is captured inside of a slot extending along a guide  100 . The slot prevents the sleeve  96  from rotating in unison with the third shaft  94 . Due to the engagement of the surface threading  95  of the third shaft  94  and the internal threading of the sleeve  96 , the sleeve  96  will move longitudinally along the third shaft  94 , as the tab  98  slides longitudinally within the slot of the guide  100 . 
     The sleeve  96  also includes a lobe  102  fixed to its outer surface. The lobe  102  travels longitudinally along with the sleeve  96 . A support  104  extends alongside the third shaft  94 . The support  104  includes mounting features, such as pilot holes, so that limit switches can be mounted on the support  104  at desired locations, in order to be tripped by the lobe  102  when the fire door  10  is at a certain stage of being opened or closed. FIG. 3 illustrates a first limit switch  106 , a second limit switch  108 , and a third limit switch  110  mounted on the support  104 . 
     In the present embodiment, the first limit switch  106  is a double pole switch, wherein both poles are normally closed. When the lobe  102  contacts the first limit switch  106 , both poles of the first limit switch  106  are opened. The second limit switch  108  is a single pole switch which is normally open. When the lobe  102  contacts the second limit switch  108 , the second limit switch  108  is closed. The third limit switch  110  is a single pole switch which is normally closed. When the lobe  102  contacts the third limit switch  110 , the third limit switch  110  is opened. 
     FIG. 6 is a close-up view of the disengageable stop or brake system  71  illustrated in FIG.  4 . The brake system  71  is responsible for asserting movement of the door, such as in the open position. If not for the brake system  71 , the weight of an open door would tend to rotate the brake disk  71  in the direction of the arrow A. In fact, the weight of the open door would ultimately rotate the rotor  130  of the motor/generator  68 , via the interconnected gears, chains and shafts, as the open door progressed to its closed position. 
     The brake system  71  includes calipers  112  having brake pads for engaging the brake disk  71 . A brake actuator, such as a lever  114  is rotateable about a pivot point  116 . 
     The lever  114  is biased in the direction of arrow B, and normally applies a force in the direction of arrow C to keep the calipers  112  in friction contact with the brake disk  71 , and thus prevent rotation of the brake disk  71 . The lever  114  is biased in the direction B by a first spring  118  which is attached to the first chain  26 , recalling that the first chain  26  is under tension as it enters the mechanical box  24 . The first spring  118  and first chain  26  constitute one embodiment of an expandable linkage. 
     Should a fire condition be sensed, slack is provided to the first chain  26 , and the lever  114  will pivot in a direction opposite to arrow B. The lever  114  will pivot due to its own weight, or, in a preferred embodiment, with the assistance of a second spring  120  attached to a fixed support  122 . When the lever  114  pivots in the direction opposite to arrow B, the calipers  112  will release the brake disk  71 , and the fire door  10  is free to move to the closed position under its own weight. 
     As a further explanation, the spring constant of the second spring  120  is less than the spring constant of the first spring  118 . By this arrangement, the lever  114 , normally resides in the position activating the calipers  112 , and thus holding the brake disk  71 . When the first chain  26  is slackened, indicating a fire condition, the second spring  120  moves the lever  114  to a release position, so that the fire door  10  will close. 
     If an operator wishes to manual test the fire door, the operator need only pull down and hold the manual release handle  62 . The manual release handle  62  is connected to the lever  114 , via a link  124 . If the manual release handle  62  is pulled, the force transmitted via the link  124  will supplement the spring constant of the second spring  120  so as to overcome the spring constant of the first spring  118 . Therefore, it can be seen that the lever  114  can be moved in the release direction, opposite to the arrow B, without having slack provided in the first chain  26 . This is particularly advantageous in that the fire door  10  can be tested without breaking or disconnecting any of the chains, fire links, or smoke detector releases above the fire door (as illustrated in FIGS.  1  and  2 ). 
     A solenoid  126  is also connected to the lever  114  via a linkage  128 . When the solenoid  126  is activated, the solenoid  126  will pull the linkage  128 . The combination of the force applied by the solenoid  126  and the spring constant of the second spring  120  is sufficient to overcome the spring constant of the first spring  118 , and allow the brake disk  71  to be released. The solenoid  126  is considered to be the primary and usual device for testing/closing the fire door  10 . The manual release handle  62  is considered to be a backup/emergency manner of testing/closing the fire door  10 . The operation of the solenoid  126  will be discussed further with reference to the electrical schematic of FIG.  7 . 
     Now, with reference to the electrical schematic of FIG. 7, several new and improved operations made possible by the present invention will be described. 
     I. Testing/Closing the Fire Door 
     First, a situation wherein the fire door  10  is in its open position, and an operator wishes to test or close the fire door  10 , will be described. The operator inserts the second electrical terminals  50  of the rechargeable battery  52  into the first electrical terminal  48  of the first control panel  42 . Next, the operator presses the second switch  46 . Typically, the second switch  46  would be labeled “test/close”, or some other similar wording. 
     The second switch  46  is a double pole switch, with both poles being normally open. So long as the fire door  10  has not yet reached its closed position (i.e., the third limit switch  110  remains closed), pressing the second switch  46  energizes the solenoid  126 . When the solenoid  126  is energized, the linkage  128  applies a force to the lever  114 , so as to supplement the spring constant of the second spring  120  and overcome the spring constant of the first spring  118 . Therefore, the lever  114  is moved, and the calipers  112  release the brake disk  71 . 
     When the brake disk  71  is free to rotate, the weight of the fire door  10  will cause the fire door  10  to move toward its closed position. Just as the fire door  10  reaches its closed position, the third limit switch  110  is contacted by the lobe  102 . When the third limit switch  110  is contacted by the lobe  102 , its normally-closed single pole is opened. When the pole is opened, power is cut to the solenoid  126 , even if the operator continues to press the second switch  46 . 
     When power is cut to the solenoid  126 , the spring constant of the first spring  118  overcomes the spring constant of the second spring  120  and the lever  114  moves to a position causing the calipers  112  to engage the brake disk  71 . Therefore, at the approximate time the fire door  10  contacts the floor (or under other circumstances, when the fire shutter contacts the countertop), the brake system  73  is engaged. This is an important advantage since momentum is built up, as the fire door  10  closes, and such momentum can overrun the mechanisms associated with deploying the fire door  10 , as discussed in connection with the background art above. Therefore, the third limit switch  108  acts to prevent overrunning of the fire door  10  in the closing direction. 
     It is also possible to test/close the fire door  10  even if the operator does not have a rechargeable battery  52  in his possession. The operator can simply pull and hold the release handle  62 , as discussed above. 
     II. Harnessing of Energy Created by the Closing Fire Door 
     As the fire door  10  travels from its open position to its closed position, the chains, gears, and shafts are driven to rotate. Ultimately, the rotor  130  of the motor/generator  68  is driven to rotate, as the fire door  10  moves to its closed position. Rotation of the rotor  130  of the motor/generator  68  causes a generator function of the motor/generator  68  to produce power. Such a motor/generator  68  can be purchased commercially, such as a Dayton DC motor, model # 4Z529. 
     The produced power is used to activate the visual indicators  64  and audible indicators  66 . Further, the produced power is fed back to a motor function of the motor/generator  68 , in such a manner as to cause the motor function of the motor/generator  68  to resist the rotation of the rotor  130 . Such an arrangement is commonly referred to as regenerative braking. 
     A variable resistor  132  is optionally placed in series with the indicators  64 ,  66 . The variable resistor  132  is useful in the initial balancing and setting up of the present invention, so as to match the regenerative braking forces produced to the dynamics of a particular fire door  10 . For example, setting the variable resistor  132  to a relative high resistance will reduce the power fed back to the motor function of the motor/generator  68 , and hence will reduce the regenerative braking. Therefore, the installer would set the variable resistor  132  relatively high when setting up the door control system of the present invention in combination with a relatively light weigh door, such as a countertop shutter conventionally found at the parts counter of an automotive dealer. 
     Of course, a variable resistor  132  is not required to practice the broad teachings of the present invention. It would be possible to install a fixed resistor at the job site, or to rely completely on the inherent resistances of the visual and audible indicators  64 ,  66 . 
     Additional optional accessories  134  can also be powered by the generator function of the motor/generator  68 , as the door closes. For example, a capacitor bank could be installed as the optional accessory  134 . The capacitor bank would store power as the fire door  10  closes. The capacitor bank would then continue powering the visual and/or audible indicators  64 ,  66  after the fire door  10  has closed. For example, the visual indicator  64  could remain lit for several minutes after the fire door  10  is closed, so as to provide lighting and directional indications to any occupants inside the building, even if the building&#39;s main AC power were out. 
     As another example, the optional accessories  134  could be a pager transmitter, which activates a pager carried by the building manager or security personnel. The pager&#39;s activation would serve as an alert that the particular fire door had been deployed. Also, the power generated could be feed to other solenoids  126  of other fire doors  10 . Such a daisy-chain arrangement would result in all of the daisy-chained fire doors  10  closing upon the closing of any one of the fire doors  10 . 
     There are limitless advantageous uses for the power produced by the closing fire door  10 . Such power is particularly advantageous in that no outside source of AC power need be operative, or even provided, in the vicinity of the fire door  10 . Yet, when the fire door  10  is tested/closed, or activated in the event of a fire, power will be present to provide lighting, alarms, instructions, etc. Therefore, a great cost savings is had since the expense of electrical wiring, ran to each and every fire door, is not required. Moreover, even if wiring were present, during a fire, power is often lost. The present invention harnesses the power transmitted from the generator function of the motor/generator  68  to power the alarms, etc. Therefore, even if power is lost, the alarm features will continue to function. 
     III. Creep Mode 
     As illustrated in FIGS. 1 and 2, a sensor strip  136  is proved on a leading edge of the fire door  10 . FIG. 8 is a cross sectional view of the sensor strip  136 . Essentially, a flexible membrane  138  encloses an elongated contact switch  140 , or a plurality of contact switches  140 . Pressure on the leading edge of the fire door  10  causes the contact switch  140  to close. 
     As illustrated in FIG. 7, the contact switch  140  is placed in parallel to one or more of the visual and audible indicators  64 ,  66 , any optional accessories  134  and any variable resistor  132 . Closing of the contact switch  140  will provide a short circuit of the power produced by the generator function of the motor/generator  68  directly to the motor function of the motor/generator  68 . Therefore, more power is fed back, and the closing speed of the fire door  10  is reduced. 
     As an example of the use of the creep mode, if a person exiting past a closing fire door  10  wishes to slow the decent rate of the fire door  10  that person need only press against the leading edge of the fire door  10 . This would be a natural reaction of a person attempting to slow the fire door  10 , i.e., push up against the door. A person might wish to slow the door&#39;s decent rate if he/she saw another person racing toward the closing fire door  10  in an attempt to exit because of a fire condition inside the building. 
     Of course other types of switches or sensors could be substituted for the contact switch  140 . For example, the flexible membrane  138  could be fluid-filled and a pressure sensitive switch could then sense increased fluid pressure caused by contact occurring at any point along the sensor strip  136 . As another example, the power produced by the generator function of the motor/generator  68  can be used to power an infrared beam or electric eye provided across the threshold of the throughway  12  or along the leading edge of fire door  10 . Any detected obstacle in the path of the closing fire door  10  will automatically place the fire door  10  into the creep mode. 
     The creep mode also plays a role in preventing overrun damage, as discussed in section I., above. Just before the fire door&#39;s leading edge contacts the floor, countertop, wall, or other relevant structure, the second limit switch  108  is contacted by the lobe  102 . The second limit switch  108  is normally open, however contact by the lobe  102  causes the second limit switch  108  to close. Closing the second limit switch  110  presents a short circuit of the power produced by the generator function of the motor/generator  68  directly to the motor function of the motor/generator  68 . Therefore, more power is fed back, and the closing speed of the door is reduced just before the fire door  10  is completely closed. By so doing, the activation of the braking system  73  when the fire door  10  is completely closed, as discussed in section I above, is more effective. 
     IV. Resetting/Opening the Fire Door 
     When an operator wishes to open/reset the fire door  10 , the operator inserts the second electrical terminals  50  of the rechargeable battery  52  into the first electrical terminal  48  of the first control panel  42 . Next, the operator presses the first switch  44 . Typically, the first switch  44  would be labeled “reset/open”, or some other similar wording. 
     The first switch  44  is a triple pole switch, with one pole being normally closed and two poles being normally open. So long as the fire door  10  has not yet reached its fully open position (i.e., the pole  1  of the first limit switch  106  remains closed), pressing the first switch  44  connects the rechargeable battery  52  to the motor function of the motor/generator  68 . When the battery  52  energizes the motor/generator  68 , the rotor  130  is rotated and via the speed reductions of the many interlinked chains, gears, and shafts, causes the slats  13  of the fire door  10  to be rolled up onto the elongated shaft  22 . 
     As the fire door  10  reaches its open position, the lobe  102  contacts the first limit switch  106 . The first limit switch  106  includes two poles, both of which are normally closed, but which open when the lobe  102  contacts the first limit switch  106 . When pole  1  of the first limit switch  106  is opened, continuity is cut between the rechargeable battery  52  and the motor/generator  68 , and motor/generator  68  stops moving the fire door  10  in the opening direction, even if the operator continues to press the first switch  44 . Therefore, pole  1  of the first limit switch  106  prevents overdriving the door in the opening direction. 
     Pole  2  of the first limit switch  106  is normally closed. When the operator is pressing the first switch  44 , the pole  2  of the first limit switch  106  provides continuity between the rechargeable battery  52  and the solenoid  126 . Therefore, as the fire door  10  is being opened, the brake system  73  is, of course, released. 
     Once the fire door  10  reaches the open position, pole  2  of the first limit switch  106  opens. Opening the pole  2  of the first limit switch  106  results in discontinuity between the rechargeable battery  52  and the solenoid  126 . When power is removed from the solenoid  126 , the brake system  73  is again engaged. Hence, the brake system  73  is engaged at the same time that power is cut to the motor/generator  68  used to move the fire door  10  to its open position, so that the fire door  10  will not fall back to its closed position. 
     The DC manner of operation, utilizing a portable battery  52 , is particularly advantageous. As mentioned in the background art section above, wiring carrying AC power is required to in order to control and open a conventional fire door. This AC wiring is expensive to provide and install, and on long runs can even exceed the cost of the fire door. Also, the background art suffers drawbacks in that AC power may be lost during a fire, and in that emergency personnel will need to carry and apply remotely powered tools or equipment to open a closed fire door. This hindrance to emergency personnel can be tragic in preventing the loss of life and/or property. 
     V. Fixed Rechargeable Battery 
     FIG. 9 illustrates an alternative embodiment of the invention. In the alternative embodiment of FIG. 9, a rechargeable DC battery  100  is not portable, but rather fixed in or near the mechanical drive box  24 . Also, in this embodiment, the first and second control panels  42 ,  54  do not include the first and third electrical terminals  48 ,  60 . All the functional capabilities of the fire door  10 , as discussed above, still apply. By the arrangement of FIG. 9, service personnel need not carry a portable rechargeable battery  52  in order to control or operate the fire door  10 . 
     A trickle charger  102  is also provided in or near the mechanical drive box  24 . The trickle charger  102  provides a small, slow DC charge to the rechargeable DC battery  100 . The trickle charger  102  would be supplied power by high gauge (low amperage) AC wiring  104 . In other words, there would be no need to run expense low gauge (high amperage) AC wiring to the fire doors  10 , since the AC wiring  104  does not supply the actual power used to operate an AC motor to lift the fire door  10 . The AC wiring  104  simply provides a low amperage current, necessary to power the trickle charger  102 . The rechargeable DC battery  100  provides the power used to operate the DC motor to lift the fire door  10 . Where possible, the trickle charger  102  could even be solar powered. 
     VI. Modifications 
     The present invention has been discussed above, and illustrated in the Figures, by way of specific examples. The present invention can be modified in many different ways, after understanding the broad teaching of the disclosure. 
     For example, the fire door illustrated in the figures has been an overhead type door, having interconnected slats, which are rolled up when stored. And, in the illustrated fire door, gravity provides the force tending to draw the fire door closed across the throughway. 
     It would be possible to have a solid fire door, or even a fire door with interconnected slats, which are not rolled up when stored (such as a common garage door which has slats, which are not rolled up when the garage door is stored overhead). Further, the fire door could be stored in its open position beneath a floor or countertop. Or, the fire door  10  could be stored in its open position in or beside a wall, lateral of the throughway to be closed. Such doors are known in the background art, and typically utilized a counterbalance weight or spring system to create the force tending to draw the fire door closed across the throughway. Moreover, the present invention, as claimed, is intended to encompass the control and operation of doors other than doors specifically designed to stop or slow the spread of fire or smoke. 
     FIGS. 3-5 illustrated a specific transmission. However, the present invention could be practiced with many variations in the transmission or with a different transmission. For example, more or less speed reduction could occur in the transmission. The teeth of the gears could be in direct contact, so as to eliminate the use of chains in the transmission. Alternatively, the gears and chains may be replaced by pulleys and belts. 
     The door position monitoring system need not be associated with the third shaft  94 . Any shaft of the transmission may be utilized. Alternatively, an encoder may be used to precisely measure the rotations of the motor/generator and hence the position of the fire door. 
     FIG. 6 illustrated a specific braking system  73 . The present invention is, of course, adaptable to many different braking systems. For example, the lever  114  need not rotate to be activated. It is envisioned that the lever  114  could be reciprocated to engage/disengage the braking system. Moreover, the entire braking system could be replaced with a completely different type of braking system. For example, a locking paw and rack could be used to arrest movement of the fire door  10 . The first and/or second springs  118 ,  120  could be replace by elastic straps, leaf springs, or other known biasing devices. 
     The electrical schematic of FIG. 7 is particularly susceptible to modification, all within the spirit and scope of the present invention, as claimed. There are many ways to interconnect various electrical elements to achieve the functions of the fire door control system of the present invention. For example, a microprocessor may be employed. Relays or timers may be used in conjunction with the first and second switches,  44 ,  46 , so that the operator need not continue to press a switch until an operation is completed. 
     The limit switches may be replaced by a potentiometer or an optically encoded shaft. Alternatively, the second limit switch  108 , which activates the creep mode, may be replace by several limit switches associated with different resistive circuits. In so doing, the regenerative braking applied to the fire door may be adjusted depending upon the progress of the fire door as it closes. For example, by applying less and less resistance in the feed-back loop, as the door closes, more and more braking is applied, so that the dynamics of the door can be accommodated, and the door will close at a substantially uniform speed. 
     The Figures have illustrated the motor/generator  68  as residing in a common housing and sharing a common rotor  130 . It is within the purview of the present invention that the motor could be provided separately from the generator. In such an instance, the motor and generator could supply and receive power, respectively, from a common shaft of the transmission, or could be connected to the transmission by different shafts. 
     The Figures have illustrated a generic rechargeable battery  52 . It is envisioned that the second terminals  50  of the rechargeable battery  52  will have specific physical characteristics adapted to particularly fit into the first terminal  48  of the first control panel  42 . For example, the physical characteristics of the rechargeable battery  52  may be in accordance with a portable power tool&#39;s rechargeable battery, such as a drill&#39;s battery. Such rechargeable DC batteries are commonly owned and carried by service personnel. 
     The operation of the present invention has been described in conjunction with the first control panel  44 . Of course, operation in a like manner could also be had using the second control panel  54 . Further, it would be possible to have only a single control panel located on one or the other side of the wall, if desired. 
     As discussed above, it will be noted that the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art, are intended to be included within the scope of the following claims.

Summary:
A door, such as a fire door or a security gate, for blocking a throughway or opening in an exterior or interior wall of a building, such as a doorway or countertop window, has an open position and a closed position. A force, such as gravity, a counter weight or a spring, tends to move the door toward its closed position. In the case of the fire door, a disengageable stop holds the door in its open position. The disengageable stop includes a brake actuator for releasing a brake. An expandable linkage, having a normal length and having an elongate length when an external force is applied thereto, has a first end connected to the brake actuator. A second end of the expandable linkage is connected to a fire condition sensitive device, which releases the second end upon a fire indicative condition. With the fire door, or any other type of door, a DC generator is connected to the door and produces power as the door moves from its open position to its closed position. A DC motor is also connected to the door and has an ability to move the door from its closed position to its open position. A first power terminal is connected to the motor, and adapted to receive a second terminal of a portable, rechargeable DC battery.