Abstract:
An automatic chute closure for covering a chute opening wherein the chute closure includes a frame disposed around a chute opening, a chute door pivotally connected to the frame for movement between an opened and closed position, a door movement mechanism for opening and closing the chute door, a switch mechanism for activating and deactivating the door movement mechanism and a latch mechanism for securing the chute door in a closed position until the switch mechanism is activated to open the chute door. The automatic chute closure allows an operator to conveniently activate a single switch to open and close the chute door and to insure once the chute door is closed it is properly locked.

Description:
This is a continuation of application Ser. No. 09/476,552 filed Jan. 3, 2000, now U.S. Pat. No. 6,186,306, which has claimed priority under 35 U.S.C. § 120 from application Ser. No. 09/081,641 filed May 20, 1998, which issued as U.S. Pat. No. 6,062,368 on May 16, 2000; and application Ser. No. 08/549,264, Oct. 27, 1995 now abandoned, each of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to the art of chute systems and, more particularly, to an automatic chute door integrated into a chute system. 
     Chute systems are commonly used to provide a convenient way of storing or disposing of various articles. Chute systems are used in medical facilities for the disposal of various types of medical products. Chute systems are also used in apartment buildings and various industries for the disposal of refuse. Chute systems are also used in homes, hotels and hospitals to store linens for later cleaning. Chute systems can further be used to separate and/or store recyclable items. 
     A typical chute system includes a chute and a storage bin. The articles are placed in the chute opening and the chute guides the articles to the storage bin for immediate or later processing. If the chute system is for waste insertion, the storage bin is typically a furnace and the articles placed in the chute are immediately processed upon entering the furnace. The chute opening can include a chute door to close the chute opening until just prior to an article being placed into the chute opening. The chute door enhances the safety and sanitation of the chute system. Medical products which are disposed in a chute system can pose potential health and/or safety risks if a chute door is not included on the chute opening. An unclosed chute opening could allow harmful and/or contaminated products to harm an individual who inadvertently comes in contact with the chute opening without proper protection. The incorporation of a chute in such facilities reduces such risks. Furthermore, chute systems used to dispose of waste are prone to fires and/or small explosions occurring in the storage bin. Such fires or explosions could cause damage to areas outside of the chute opening if a chute door is not used. The use of a chute door also reduces and/or prevents gases and/or fine particles in the chute and storage bin from escaping through the chute opening, especially where such gases and/or particles are noxious, harmful and/or infectious. Furthermore, chute doors are used to prevent children from injury due to climbing in and playing around a chute opening. 
     Although past chute systems have commonly employed chute doors, these prior chute door&#39;s designs have proven to be, in many cases, safety risks in-of-themselves. Many of the chute doors used in the disposal of refuse are not fire rated to resist exposure to a fire or made durable enough to withstand an explosion in the storage bin. As a result, damage to facilities outside the chute opening are not always avoided in the case of fire. Further, small explosions in the storage bin result in the chute door being inoperably damaged and/or destroyed. Furthermore, chute doors that have been designed to be fire resistant and/or explosion resistant have not been designed to properly seal the closure opening from releasing flames caused by a fire and/or from releasing gases various chemicals within the storage bin. In addition, prior chute doors typically do not include a latch mechanism to secure the chute door from being jarred open when an explosion occurs in the chute or storage bin. Chute doors which have included latch mechanisms have suffered from complicated designs and/or unreliable latching of the chute door. As a result, the chute door remains unsecure thus not providing the proper security the chute door was originally designed for. 
     In view of the past design and safety deficiencies of prior chute closures, there is a need to provide a chute door which is easily operable and ensures a secure closure to prevent the chute door from inadvertently opening due to a fire and/or explosion in the storage bin and further seal the chute opening from releasing flames and/or gases when the chute door is in the closed position. 
     THE SUMMARY OF THE INVENTION 
     In accordance with the present invention, an improved chute system is provided which minimizes and/or overcomes the foregoing disadvantages of prior chute systems heretofore available while, at the same time, maintaining the advantage of simplicity of use with respect to opening and closing the chute door and insuring the chute door is properly closed. 
     More particularly, in accordance with the present invention, a chute system is provided which includes a chute closure for covering a chute opening. The chute closure includes a frame disposed about the chute opening, a chute door pivotally connected to the frame for moving between a closed position and an open position, a door movement mechanism for opening and closing the chute door, a switch mechanism for activating and deactivating the door movement mechanism and a latch mechanism for securing the chute door in a closed position until the switch mechanism is activated to open the chute door. The improved assembly for a chute closure allows an operator to conveniently activate a single switch to open and close the chute door. The improved assembly also ensures that when the chute door is closed, the chute door is properly secured in the closed position and will not inadvertently open until the operator activates the switch mechanism to open the chute door. The latch mechanism is preferably integrated with the door movement mechanism to insure for proper latching of the chute door when the operator activates the chute system to close the chute door. The latch mechanism is designed to insure the chute door will not inadvertently open when a fire and/or an explosion occurs in the storage bin. The chute door is preferably connected to the base of the frame to pivot about the base of the frame. The chute system is preferably made of fire resistant materials such as carbon steel and stainless steel to prevent or reduce damage to the chute system and ensure the chute system complies with safety guidelines in the event of a fire and/or explosion in the chute and/or storage bin. 
     In accordance with another aspect of the present invention, the latch mechanism includes a latch bolt which is integrated into the chute door. The latch bolt engages the frame of the chute system when the chute door is in the closed position thereby preventing the chute door from inadvertently opening. The latch bolt is also designed to be easily disengaged from the frame of the chute system when the operator activates the switch mechanism to open the chute door. The latch mechanism is preferably integrated with the door movement mechanism so that the activation of the door movement mechanism also activates the latch mechanism to latch and unlatch the chute door from the door frame. The integration of the latch mechanism with the door movement mechanism insures that the latch bolt is properly retracted when the operator activates the chute door to be opened, insures that the latch bolt is properly engaged with the chute door frame when the chute door is moved to the closed position by the door movement mechanism and simplifies the locking and unlocking of the chute door. 
     In accordance with another aspect of the present invention, the chute door includes a flange positioned about the peripheral edge of the chute door to cover any space between the chute door and the frame of the chute closure when the chute door is in the closed position. The flange preferably includes a sealing material to reduce or prevent flames, smoke and/or noxious gases from escaping along the side of the chute door when the chute door is in a closed position. The flange is preferably designed to also provice a barrier against flames or a rush of gases from projecting from the chute door when an explosion and/or fire has occurred in the storage bin. The flange is preferably made of materials similar to the chute door. The sealing material is preferably composed of a rubber or plastic material. 
     In accordance with another aspect of the present invention, the door movement mechanism includes an electric motor which is connected to the switching mechanism for controlling the opening and closing of the chute door. The electric motor is preferably a linear motion motor. The use of a linear motion motor reduces the space needed for the door movement mechanism and further simplifies and enhances the operation of the door movement mechanism. 
     In accordance with another aspect of the present invention, the door movement mechanism includes a counter balance which continues the weight of the chute door during the opening and the closing of the chute door. The counter balance is preferably designed to essentially neutralize the weight of the chute door during the opening and closing of the chute door. If the counter balance is used in conjunction with an electric motor, the counter balance allows for a smaller sized electric motor to be used for the opening and the closing of the chute door. Preferably, the counter balance is a gas spring. Preferably, the gas spring counter balance is integrated with linear motion motor in the door movement mechanism. 
     In accordance with another aspect of the present invention, a switch mechanism is incorporated in the chute system and includes an actuator switch, when activated by an operator, activates the door movement mechanism to open or close the chute door. The switch mechanism preferably includes a control mechanism for deactivating the door movement mechanism when the chute door is indicated to be in the open position or indicated to be in the closed position. Such a control mechanism prevents the electric motor from continuing to work even though the chute door is in the complete open position or the complete closed position. Preferably, the switch mechanism also includes a timer mechanism to shut off power to the electric motor after a certain period of time has elapsed after the actuator switch has been activated. The timer mechanism prevents the electric motor from continuing to work when the chute door inadvertently jams in a partially open position or the indicators which indicate a completely open or closed chute door have malfunctioned. 
     It is an object of the present invention to provide a chute system which include a chute door that can be easily operated. 
     It is another object of the present invention to provide a chute system of the foregoing character which includes chute door which remains in a closed position when a fire or explosion occurs in the chute and/or storage bin. 
     It is yet another object of the present invention to provide a chute system of the foregoing character which includes a chute door closure which is fire resistant. 
     It is still yet another object of the present invention to provide a chute system of the foregoing character which includes an automatic chute door which is opened and closed by an electric motor and a counter balance. 
     It is another object of the present invention to provide a chute system of the foregoing character which includes a control mechanism which indicates when the chute door is in an open and closed position and further prevents continued working of an electric motor the chute door is jammed in a partially opened position or one of the chute door position indicators has malfunctioned. 
     it is yet another object of the present invention to provide a chute system of the foregoing character which includes a lock mechanism integrated with a door movement mechanism to insure that the chute door is properly unlatched and latched in its respective open and closed positions. 
     It is another object of the present invention to provide a chute system of the foregoing character which reduces flames and/or gases from exiting the chute opening by way of the chute door. 
     It is still another object of the present invention to provide a chute system of the foregoing character which is easy to operate, maintain and install. 
     These and other objects and advantages will become apparent to those skilled in the art upon reading the following description taken together with the accompanying drawings. 
    
    
     THE BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference may now be made to the drawings, which illustrate various embodiments that the invention may take in physical form and in certain parts and arrangement of parts wherein: 
     FIG. 1 is a front view of the door closure of the present invention and further illustrates the timer controller and power supply integrated therewith; 
     FIG. 2 is a block diagram of the control system for the invention of FIG. 1; 
     FIG. 3 is a partial perspective view of the invention of FIG. 1, partially in section, which illustrates the chute door movement arrangement; 
     FIG. 4 is a partial perspective view of the chute closure as disclosed in FIG. 3 wherein the chute door is in the open position; 
     FIG. 5 is a cross-sectional elevation view taken along line  5 — 5  of FIG. 3; 
     FIG. 6 is a cross-sectional elevational view taken along line  6 — 6  of FIG. 5; 
     FIG. 7 is a side view of the invention as shown in FIG.  5  and illustrates the movement of the chute door movement arranged just prior to the opening of the chute door; 
     FIG. 8 is a side elevation view of the invention as shown in FIG.  5  and illustrates the movement of the chute door movement arrangement for the chute door in the complete open position; 
     FIG. 9 is an enlarged cross-sectional elevation view taken along line  9 — 9  of FIG. 6; 
     FIG. 10 is a cross-sectional view taken along line  10 — 10  of FIG. 9; 
     FIG. 11 is an alternate position of the view as shown in FIG. 9; and, 
     FIG. 12 is a cross-sectional view taken along line  12 — 12  of FIG.  11 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, wherein the showings are for the purpose of illustrating the preferred embodiment of the invention only and not for the purpose of limiting the same, in FIG. 1 there is illustrated a chute closure  20  which includes a chute door  22  and frame  24 . Frame  24  is formed to be mounted on a generally flat surface  46  and to surround the chute opening. As shown in FIG. 1, frame  24  is generally rectangular in shape and supports a generally rectangular chute door  22 ; however, frame and chute door are not limited to any particular shape. Frame  24  is preferably made of a durable and flame resistant material such as carbon steel and/or stainless steel. Frame  24  defines a generally rectangular chute opening. Frame  24  also includes a frame flange  26 . Frame flange  26  is connected to at least the top of frame  24  and is used to secure frame  24  to surface  46 . Frame  24  also includes a front panel  27  positioned next to chute door  22 . Front panel  27  provides access to the movement mechanism of the chute door. Panel bolts  25  are inserted through panel  27  to secure the front panel to frame  24 . 
     As illustrated in FIGS. 1 and 2, chute door  22  is preferably opened and closed by an electric motor  62 . As will be described in more detail below, electric motor  62  is preferably part of a linear motion actuator  60 . The electric motor is preferably a 24 Volt DC motor which is powered by power supply  142  and is controlled by timer controller  140  when switch  50  is activated by an operator. Power supply  142  is preferably a 24 volt DC power supply. As illustrated in FIG. 2, timer controller  140  receives input from several sources and directs power from power supply  142  to motor  62  to control the opening and closing of chute door  22 . Timer controller  140  receives input from upper limit switch  52 , lower limit switch  56  and switch  50 . Switch  50  is preferably an Allen-Bradley standard push button switch. The lower limit and upper limit switches are preferably micro-switches. The timer controller is preferably a Magnescraft Time Delay Off Switch (0-30 seconds) 120 Volts. When switch  50  is actuated by an operator, timer controller  140  directs power from power supply  142  to motor  62 . Timer controller  140  continues to allow power to be directed to motor  62  until a limit switch  52  indicates that the chute door  22  is in the closed position or the complete open position. In the design of the present invention, the lower limit switch  56  indicates that chute door  22  is in the closed position and upper limit switch  52  indicates that the chute door  22  is in the complete open position. Timer controller  140  preferably includes an internal timer to terminate power to motor  62  after a certain period of time has elapsed after switch  50  has been actuated. This time out sequence in timer controller  140  prevents motor  62  from burning out when chute closure  20  has been jammed in a partially opened position or timer controller  140  has not properly received the signal from upper limit switch  52  or lower limit switch  56 . Preferably, the internal timer is set at no more than 30 seconds. 
     Referring now to FIG. 3, the chute door movement mechanism is disclosed in detail. The chute door movement mechanism is preferably located behind the front panel  27  which is shown in FIG.  1 . Front panel.  27  is bolted onto frame  24  by panel bolts  25  which are inserted into bolt holes  23 . Front panel  27  can be easily removed by the removal of panel bolts  25  to allow maintenance to be performed on the chute door movement mechanism. As discussed above, chute door  22  is preferably opened and closed by an electrical, mechanism. Preferably, a linear motion actuator  60  is used for the chute door movement. Linear motion actuator  60  includes a motor  62 , an actuator cylinder  64  and an actuator piston  66  which linearly moves within actuator cylinder  64 . Preferably, the linear actuator is a 24 volt DC linear ball-driven motor actuator. The linear actuator is connected to frame  24  by motor bracket  68 . Preferably, linear motion actuator  60  is pivotally attached to motor bracket  68  to allow the linear actuator to move as actuator piston  66  is retracted and withdrawn in actuator cylinder  64  during the opening and closing of chute door  22 . The end of actuator piston  66  is connected to motor bar  106  which in turn is connected to coupling bar  104 . 
     The chute door movement mechanism also includes an air spring  70  which is made up of a spring cylinder  72  and a spring piston  74 . Air spring  70  is pivotally mounted to front panel  27  by spring bracket  76 . As best shown in FIG. 5, air spring  70  is stabilized by spring guide  78 . Spring guide limits the movement of air spring  70  so that the air spring properly pivots on spring bracket  76 . Spring guide  78  is preferably mounted to the inside surface of front panel  27 . As is well known, and therefore not illustrated in the detail, the lower end of spring piston  74  extends into spring cylinder  72  and is attached to a piston which is reciprocal within the cylinder. As is further well known, such air springs are self-contained units charged with a suitable gas under pressure, such as nitrogen, and which gas is operable on opposite sides of the piston through a valving arrangement to control relative displacement between the piston and cylinder in response to a load which extends or retracts the piston rod relative to the cylinder. A gas pressure in the cylinder is selected to give a desired control based on the weight of the load, and in connection with the preferred embodiment herein illustrated and described, the air spring is designed to act as a counter weight to neutralize the weight of the chute door  22  during the opening and closing thereof. The upper end of spring piston  74  is pivotally connected to balance bar bracket  102  which in turn is rigidly connected to counter balance bar  100 . The lower end of counter balance bar  100  is pivotally connected to coupling bar  104 . 
     Coupling bar  104  includes a lower switch arm  120  which extends from coupling bar  104 . Lower switch arm  120  is designed to contact lower switch bar  58  of lower limit switch  56  when chute door  22  is in the closed position. The interaction between lower switch arm  120  and lower limit switch  56  will be described in more detail hereinafter. 
     The lower end of coupling bar  104  is pivotally connected to coupler flange  94  which in turn is rigidly connected to pivot coupler  92 . Pivot coupler  92  is designed to rotate about chute pivot bar  90 . Chute pivot bar  90  is rigidly attached to frame  24  by pivot bar bracket  96 . Chute door  22  is rigidly attached to pivot coupler  92  so that the chute door pivots about the base of frame  24 . As described in more detail below, chute door  22  is opened by coupling bar  104  raising coupler flange  94  which in turn causes pivot coupler  92  to rotate about chute pivot bar  90  causing chute door  22  to rotate in an open position as disclosed in FIG.  4 . 
     As best illustrated in FIG. 5, upper limit switch  52  is mounted to the inner surface frame  24  near the top of the frame. Upper limit switch  52  includes an upper switch bar  54  and an upper switch arm  122  rigidly mounted to upper switch bar  54 . 
     As best illustrated in FIGS. 4 and 8, chute door  22  includes a chute front panel  30 , chute side  34  and a chute back panel  36 . Chute door  22  is designed to resist damage by fire and large forces such as from an explosion. Chute door  22  is preferably made of a 16 gauge 304 stainless steel and/or 16 gauge cold rolled steel. An insulating material may be disposed between the front and back panels of the chute door to reduce the amount of heat transferred from the back panel of the chute to the front panel when the back panel of the chute is exposed to fire and extreme temperatures. Chute door  22  also includes two chute side panels  32  mounted near the intersection of chute back  36  and chute side  34 . Chute side panels  32  are incorporated onto chute door  22  to guide materials through the chute opening when chute door  22  is in the open position. 
     Referring now to FIG. 10, chute side  34  includes a latch bolt  80  slidably positioned between a face plate  82 . Face plate  82  is mounted to chute side  34  by two plate screws  88 . Latch bolt  80  slidably moves into and out of bolt housing  84 . Latch bolt  80  is biased in the outward position by bolt Spring  86 . Latch bolt  80  includes a tapered end  81 . Tapered end  81  is positioned such that it faces away from the inner surface of frame  24 . The operation of the latch bolt with respect to the opening and closing of chute door  22  will be described below. 
     Chute door  22  also includes a flange  40  attached to the outer edge of chute front panel  30 . The flange  40  extends sufficiently outward to cover the space between chute door  22  and the chute opening when the chute door is in the closed position. The interior of flange  40  preferably includes a chute seal  42  which contacts the surface of frame  24  when chute door  22  is in the closed position. Chute seal  42  reduces or prevents gases, odors and flames from penetrating through the space between the chute door  22  and frame  24  when chute door  22  is in the closed position. Chute seal  42  preferably is made of a rubber material and is preferably attached to flange  40  by an adhesive substance. 
     Referring now to FIGS. 6-12, latch arm  130  is moveably mounted on frame side wall  29  by arm pin  134 . Latch arm  130  includes a set screw  132  which rigidly attaches latch arm  130  to arm pin  134 . Arm pin  134  extends through frame side wall  29  and is attached to latch bar  108  which in turn is rotatably attached to coupling bar  104 . The front edge of latch arm  130  includes an arm tapered surface  136 . As described more fully below arm, tapered surface  136  is designed to engage latch bolt  80  and cause latch bolt  80  to retract into bolt housing  84 . As shown in FIG. 10, chute door  22  is in a closed position wherein chute seal  42  is in contact with frame  24  and chute door  22  is secured in the closed position by latch bolt  80 . As shown in FIGS. 11 and 12, latch arm  130  is mounted to rotate downwardly such that arm tapered surface  136  can contact latch bolt  80  and force latch bolt  80  to retract within bolt housing  84  located in chute door  22 . The retraction of latch bolt  80  from frame  24  allows chute door  22  to be opened. 
     The operation of the automatic chute door will now be described. As best illustrated-in FIG. 10, chute door  22  is maintained in a closed locked position by latch bolt  80 . Latch bolt  80  insures that chute door  22  remains closed even when an inadvertent force, such as from an explosion, is applied to the chute back panel  36 . As seen from FIG. 10, a force applied onto chute door  22  from chute back side  36  will cause latch bolt  80  to engage with frame  24  thus maintaining chute door  22  in a closed position. 
     Chute door  22  is opened by an operator depressing switch  50  located on front panel  27 . The pressing of switch  50  sends a signal to timer controller  140 . Upon receiving the signal from switch  50 , timer control  140  begins its preset time delay count down and directs power from power supply  142  to energize motor  62  of the linear motion actuator  60 . Motor  62  causes actuator piston  66  to begin retracting into actuator cylinder  64  as shown in FIG.  7 . The retraction of actuator cylinder  62  causes motor bar  106  to begin lifting coupler bar  104 . 
     As best illustrated in FIG. 5, coupler bar  104  includes a coupling bar slot  110  which allows for coupling bar to be moved slightly upward prior to applying an upward force to coupler flange  94 . The small upward movement of coupler bar  104  allowed by coupling bar slot  110  allows latch arm  130  to engage with latch bolt  80  to cause latch bolt  80  to retract within bolt housing  84 . As best shown in FIG.  5  and FIG. 7, as coupling bar  104  is raised, coupling bar  104  forces latch bar  108  to begin rotating. The rotation of latch bar  108  thereby causes arm pin  134  to rotate which in turn causes latch arm  130  to rotate downwardly toward latch bolt  80  as illustrated in FIG.  7 . The size of coupling bar slot  110  is of sufficient length. to allow coupler bar  104  to be sufficiently raised to cause latch arm  130  to fully retract latch bolt  80 . 
     Once latch bolt  80  has been properly retracted as illustrated in FIG. 12, coupler bar  104  begins to move coupler flange  94  upwardly thereby causing pivot coupler  92  to rotate about chute pivot bar  90 . The rotation of pivot coupler  92  in turn causes chute door  22  to begin opening. 
     As shown in FIGS. 7 and 8, when coupling bar  104  begins moving coupler flange upwardly, coupler bar  104  simultaneously begins to move counter balance bar  100  in the upward position. As counter balance bar  100  is moved in an upward position, spring piston  74  begins to extend from spring cylinder  72 . Due to the design of air spring  70 , spring piston  74  resists being extended from spring cylinder  72 . This resistance creates a counter balancing effect to the weight of chute door  22  as chute door  22  moves to the open position. The counter balancing effect of air spring  70  to chute door  22  allows linear motion actuator  60  to smoothly operate during the opening of chute door  22 . Although linear motion actuator  60  is designed to open chute door  22 , a much larger linear actuator would be needed to both open and close the chute door due to the significant weight of the chute door if air spring  70  was not used. By use of the air spring as a counter weight, the size of the linear motion actuator can be significantly reduced thereby simplifying the design of the automatic chute closure and reducing the amount of energy necessary to open and close the chute door  22 . 
     Referring now to FIG. 8, motor  62  continues to retract actuator piston  66  into actuator cylinder  64  until coupling bar top edge  112  contacts upper switch arm  122  which in turn moves upper switch bar  54  thereby activating upper limit switch  52 . The activation of upper limit switch  52  sends a signal to timer control  140  thereby causing timer control  140  to terminate the power supply to motor  62 . The positioning of upper limit switch  52  is such that the contact of coupling bar top edge  112  with upper switch arm  122  indicates when chute door  22  is in the complete open position as illustrated in FIG.  8 . Once chute door  22  is in the complete open position, materials such as linens, refuse, disposable medical products, etc. are directed through the chute opening for disposal in the storage bin located at the end of the chute. If for some reason chute door  22  was jammed during opening thereby preventing coupling bar top edge from contacting upper switch arm  122 , timer controller  140  would continue to direct power to motor  62  until the internal timer timed out. The timing out of the internal timer would cause timer controller  140  to terminate power to motor  62 . Timer controller  140  would also terminate power to motor  62  if upper limit switch did not properly send a signal to the. timer controller  140  when coupling bar top edge  112  contacted upper switch arm  122 . As is apparent, the timer controller has a safety backup to prevent the motor from continually running and overheating. 
     The chute door is closed as easily as it is opened by the operator once again depressing switch  50 . Upon the activation of switch  50 , timer controller  140  is once again activated thereby directing power from power supply  142  to energize motor  62 . Motor  62  causes actuator piston  66  to begin extending from actuator cylinder  64 . As actuator piston  66  extends from actuator cylinder  64 , actuator piston  66  causes motor bar.  106  to force coupling bar  104  downwardly. The downward motion of coupling bar  104  causes coupler flange  94  to downwardly rotating which causes chute door  22  to begin moving toward the closed position. The downward movement of coupling bar  104  also causes counter balance bar  100  to move in a downwardly position. The downward position of counter balance bar  100  in turn causes spring piston  74  to begin to retract within spring cylinder  72  of air spring  70 . Because of the design of air spring  70 , the counter balance effect of air spring  70  assists in the closing of chute door  22 . Actuator piston  66  continues to force coupling bar  104  into a downward position until lower switch arm  120  contacts lower switch bar  58  which in turn activates lower limit switch  56 . The activation of lower limit switch  56  causes a signal to be sent to timer control  140  which in turn causes timer control  140  to terminate the power supply to motor  62 . 
     As chute door  22  is nearly closed, tapered end  81  of latch bolt  80  contacts the front edge of frame  24 . Chute door  22  proceeds to close since tapered end  81  is designed to cause latch bolt  80  to slidably retract into bolt housing  84  as the chute door  22  is moved into the closed position. Once latch bolt  80  has moved beyond the edge of frame  24  as shown in FIG. 10, latch bolt  80  moves out of bolt housing  84  to become fully extended due to the biasing effect of bolt spring  86 . The extension of latch bolt  80  as shown in FIG. 10 prevents chute door  22  from being opened. until an operator once again activates switch  50 . If during closing, timer controller  140  does not receive a signal from lower limit switch  56 , the internal timer will time out causing timer controller  140  to terminate power to motor  62 . 
     The invention has been described with reference to a preferred embodiment and alternates thereof. It is believed that many modifications and alterations to the embodiments disclosed will readily suggest themselves to those skilled in art upon reading and understanding the detailed description of the invention. It is intended to include all such modifications and alterations insofar as they come within the scope of the present invention.