Abstract:
A performance venue having a dynamic load management system for use in managing loads. The system uses a dead man circuit as a means for determining the actual or anticipated dynamic load produced by moving loads, and then disables the system by opening the dead man circuit when too many loads are moved or selected to be moved. Preferably, the invention is embodied in a dead man circuit is pure hardware, and is free of software components. The invention also provides a method of controlling movement of loads in a performance venue having a plurality machines. In its basic form, the method comprises selecting at least one of the machines for movement, closing a dead man circuit, and opening the dead man circuit if the current in the dead man circuit falls outside a predetermined range.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to entertainment venues that have multiple mechanical loads being moved, such as lighting, scenery, curtains, etc., and specifically to a system for controlling movement of the loads. 
       BACKGROUND OF THE INVENTION 
       [0002]    Performance venues such as theaters, arenas, concert halls, auditoriums, convention centers, television studios, and the like can employ battens or trusses to raise and lower lighting, scenery, set-pieces, displays, draperies, and other items. Lift assemblies, or hoists, are typically used to raise and lower battens or trusses and attached loads. The lift assemblies are commonly connected directly to the support structure of a building, for example, to overhead beams. In some lift systems, multiple lift assemblies, or machines, can be employed for moving heavy loads, and can be connected to the same support structure. 
         [0003]    Variable numbers of lift machines can be selected to operate for moving particular loads, such as a stage curtain and scenery. In a situation in which the stage curtain and scenery need to be raised at the same time, two lift machines can be selected to operate simultaneously. When multiple lift assembly machines are started, stopped, sped up, or slowed down at the same time, the moving mass and inertia of the machines and attached loads can place a large dynamic load on the support structure. As used herein, “dynamic load” refers to a dynamic mechanical load created by the acceleration or deceleration of a mass. For example, dynamic load on a building structure can be created by the force exerted by the inertia of starting, stopping, speeding up, or slowing down one or more accessories connected to the structure. 
         [0004]    In locations where lift assemblies are installed, for example, to the “flytower” above a stage, the building support structure is often designed to handle the dynamic load of only a few lift machines starting and/or stopping at the same time. If too many lift machines are started and/or stopped at the same time, the associated dynamic load can cause damage to the support structure. Accordingly, the number of machines that are started or stopped at the same time may need to be limited in order to limit the dynamic load created. 
         [0005]    Lift assembly systems that employ multiple lift machines often include a primary safety mechanism to prevent excessive dynamic loading on the support structure when the machines are started or stopped. Generally, such safety mechanisms are controlled through software. One risk of a software-based safety mechanism is that the software can malfunction or fail due to loss of power, inherent or acquired bugs, misuse by an operator, or other reasons. Thus, it is often desirable to have a dynamic load safety backup system that prevents the start of too many machines. 
         [0006]    Some conventional multi-machine lift systems utilize an operator-activated safety backup mechanism to avoid overloading the building support structure to which a system is connected when multiple machines are started, stopped, or speed changed at the same time. For example, when signaled that an excessive dynamic load is being exerted by start-up of multiple machines, an operator can hit an “emergency stop” button to shut off power and stop operation of the machines. A significant disadvantage of such an operator-activated safety mechanism is that simultaneously stopping operation of multiple machines can suddenly release the excessive dynamic load in one direction and thereby create an excessive dynamic load on the support structure in the opposite direction. Another disadvantage is that such an operator-activated safety backup mechanism is engaged “after the fact,” following initiation of an excessive dynamic load, and is dependent upon an operator monitoring for an excessive load. 
         [0007]    Some conventional multi-machine lift systems utilize a software-based program as a safety backup mechanism to avoid an excessive dynamic load. Such software allows only a limited number of machines to be selected for movement at one time. One disadvantage of a software-based safety mechanism is that the software can malfunction or fail due to bugs in the software, or when used in applications that exceed software parameters. Another disadvantage of such a software-based safety mechanism is that certifying such systems for safety according to regulatory and/or industry standards can be complicated (if not impossible), time-consuming, and costly. 
       SUMMARY 
       [0008]    The present invention provides a dynamic load management system that is particularly suited for use in managing the loads present in a performance venue, such as a theatre, auditorium, stage, television set, convention center, or any other similar forum. More specifically, the present invention is designed to use a dead man circuit as a means for determining the actual or anticipated dynamic load produced by moving loads, such as lighting, scenery, set-pieces, displays, draperies, and other items, and then disabling the system by opening the dead man circuit when too many machines are moved or selected to be moved. The system can be a primary dynamic load management system, or it can be a secondary or fallback system. 
         [0009]    In one embodiment the invention is found in a performance venue comprising a plurality of machines (e.g., hoists) designed to move loads, a control center, a communication link coupling the control center to the machines, a machine switch (e.g., in each machine) coupled to the communication link and movable between an open position and a closed position, and a dead man circuit. The dead man circuit comprises a dead man enable switch movable between an open position and a closed position, a switching element (e.g., in each machine) coupled to the machine switch and operable to move the machine switch to the closed position, and a dead man trip that will open the dead man circuit when current in the dead man circuit is outside a desired range (e.g., when the actual current exceeds a max current). In a preferred embodiment, the dead man trip includes a current measuring device, a comparator coupled to the current measuring device, a trip contact, and a hold unit designed to hold the trip contact open when it is tripped. 
         [0010]    Preferably, the control center includes a system controller coupled to the communication link and operable to provide a machine select command to each of the machines. In this design, each machine can include a machine controller coupled to the communication link and operable to receive the machine select command. The dead man circuit can further include a unit select switch corresponding with each machine, and wherein each machine controller is operable to move a corresponding unit select switch to a closed position. The dead man circuit preferably includes a plurality of parallel branches corresponding with the plurality of machines, each branch including a unit select switch, a switching element, and a current sink. In its most-preferred embodiment, the dead man circuit is pure hardware and is free of software components. 
         [0011]    The present invention can also be found in a method of controlling movement of loads in a performance venue having a plurality machines for moving the loads. In its basic form, the method comprises selecting at least one of the machines for movement, closing a dead man circuit (e.g., by pressing a dead man button), and opening the dead man circuit if the current in the dead man circuit falls outside a predetermined range. Preferably, the dead man circuit includes a trip contact, and the step of the dead man circuit includes measuring the current in the dead man circuit, comparing the measured current to a maximum current, and opening the trip contact if the measured current exceeds the maximum current. 
         [0012]    Features of a dynamic load management system and/or method may be accomplished singularly, or in combination, in one or more of the embodiments of the present invention. As will be realized by those of skill in the art, many different embodiments of a dynamic load management system and/or method are possible. Additional uses, advantages, and features of aspects of the present invention are set forth in the illustrative embodiments discussed in the detailed description herein and will become more apparent to those skilled in the art upon examination of the following. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a perspective view of a theatre stage having several accessories and corresponding machines for moving the accessories. 
           [0014]      FIG. 2  is a schematic illustration of a dynamic load management system used to operate and control the lift machines in  FIG. 1 . 
           [0015]      FIG. 3  is a flowchart of a process for operating the dynamic load management system in  FIG. 2 . 
           [0016]      FIG. 4  is a diagram of machine circuitry usable in the dynamic load management system and method in  FIGS. 1-3 . 
           [0017]      FIG. 5  is a diagram of control center circuitry usable in the dynamic load management system and method in  FIGS. 1-3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]      FIG. 1  illustrates an performance venue in the form of a theatre. The theatre includes a stage  10  and overhead rigging  12  for movement of loads/accessories  14 , such as scenery, lighting, curtains, set-pieces, displays, or any other entertainment accessory that might be used for an entertainment event. The overhead rigging is secured to overhead support members in the form of I-beam trusses  16 , which are commonly present in entertainment venues. The rigging includes multiple lift machines  18  (e.g., hoists) that each includes a motor  20  that provides movement to an accessory. A particular theatre can include a large number of separate machines  18  and corresponding accessories. Such lift machines  18  are more fully described in co-owned, co-pending U.S. Patent Application No. 61/262,244, which is incorporated herein by reference in its entirety. 
         [0019]    Referring to  FIG. 2 , in the illustrated embodiment, the machines  18  are controlled by a dynamic load management system having a control center  22 , as shown in  FIG. 2 . The control center  22  includes a system controller  24  that is coupled to the machines  18  by a communication link  26 , such as a serial bus. The system controller  24  is designed to receive input (e.g., from a user or from a software program) and initiate controlled movement of the machines  18  in a programmed manner. The system controller  24  can send at least two types of commands to the machines  18  via the communication link  26 . The control center  22  can send a machine select command to the machines  18  to indicate to the signaled machines  18  that those machines  18  have been selected for movement. The control center  22  can also send a movement command to the selected machines  18  to cause the machines  18  to move under the desired conditions. 
         [0020]    The communication link  26  is coupled to a machine controller  28  in each of the machines  18 . The machine controller  28  is wired to the motor  20  of the corresponding machine  18  through a machine control link  30 , which passes through a normally-open switching element  32 . 
         [0021]    The system controller  24  can be programmed in a variety of ways to achieve a software-based load management system. For example, the system controller  24  can be programmed such that select commands and movement commands can only be sent out to a limited number of machines  18  at any given time. In this way, the system provides a means for limiting the dynamic mechanical load that will be placed on the performance venue structure (e.g., that might be caused by simultaneous starting or stopping multiple machines  18 ). 
         [0022]    A dead man circuit  34  is coupled between the control center  22  and the machines  18  to provide a hardware system for limiting the number of machines  18  that can be operated at any given time, thereby limiting the dynamic load created by the corresponding accessories. The illustrated dead man circuit  34  is hard-wired between the control center  22  and the machines  18 , and includes no software for operation. In this regard, when the system controller  24  includes a programmed means for limiting the number of machines  18  that can be operated at any given time, the hardware system described below acts as a backup to the software system. 
         [0023]    The portion of the dead man circuit  34  in the control center  22  includes a supply voltage  36 , a dead man enable switch  38 , and a dead man trip  40 . The illustrated supply voltage  36  is a twenty-four volt source. The dead man enable switch  38  is normally open and can be manually closed by a user by pressing a dead man button  42 . As with a typical dead man enable switch  38 , the button  42  must be held by the user throughout the time that machines  18  are moving. 
         [0024]    The closing of the dead man circuit  34  is sensed and communicated to the system controller  24  through a dead man status link  43 . This information is used by the system controller  24  as an indication that the system is ready for machines  18  to move, and thus movement commands can be sent to the appropriate machines  18 . In the illustrated embodiment, the system controller  24  is programmed with a slight delay (e.g., 100-200 mSecs) between the time it senses that the dead man circuit  34  is ready and the time it sends the movement commands. This delay provides sufficient time for the current in the dead man circuit  34  to stabilize, as described below in more detail. 
         [0025]    The dead man trip  40  is a hardware device that will open the dead man circuit  34  if the current in the circuit exceeds a predetermined value. The dead man trip  40  includes a trip contact  44 , a current measuring device  46 , a comparator  48 , a max current source  50 , a hold unit  52 , and a reset unit  54 . The trip contact  44  is a normally closed switch that is coupled to the hold unit  52 . The illustrated current measuring device  46  and shunt resistor (R-102) is a high side current measuring device that produces an output voltage corresponding with the current in the dead man circuit  34 . The illustrated comparator  48  is an op-amp comparator that receives inputs from the current measuring device  46  and from the max current source  50 . If the current in the dead man circuit  34  exceeds the current from the max current source  50 , the output of the comparator  48  will cause the trip contact  44  to open. The hold unit  52  will maintain the trip contact  44  in the open position until it is manually reset by a user pressing a reset button  56  of the reset unit  54 . 
         [0026]    As noted in more detail below, in the illustrated embodiment, when a machine  18  is selected, it will draw 10 mA in the dead man circuit  34 . If it is desired to limit the number of selected machines  18  to four, then the maximum current source  50  will be set between 40 mA and 50 mA (e.g., about 45 mA), which will not trip the comparator  48  when four machines  18  are selected (producing 40 mA current in the dead man circuit  34 ), but will trip the comparator  48  when five machines  18  are selected (producing 50 mA in the dead man circuit  34 ). In the illustrated embodiment, the max current source  50  can be adjusted depending on the structural integrity or strength of the building into which the system is being installed. In one embodiment, the max current source is a hardware jumper that has four levels, corresponding with the maximum selection of 2, 4, 6, or 8 machines. 
         [0027]    As shown in  FIG. 2 , the dead man circuit  34  also includes a parallel loop  60  in each of the machines  18 . Each parallel loop  60  includes a unit select switch  62  that is normally open and is only closed when instructed by the corresponding machine controller  28 . In this regard, the machine controller  28  can be coupled to the unit select switch  62  by an opto-coupler  64  in order to electrically isolate the machine controller  28  from the dead man circuit  34 . 
         [0028]    Each parallel loop  60  further includes a current sink  66  that draws a predetermined current. The current drawn by each current sink  66  represents the “load” of the corresponding machine  18  and related accessory. In the illustrated embodiment, each current sink  66  draws 10 mA, and thus each of the loads is approximated to be the same for purposes of the dead man circuit  34 . It should be appreciated, however, that the size (i.e., current draw) of each current sink  66  could be designed to be proportional to the actual mechanical load of the corresponding machine  18  and accessory. 
         [0029]    Each parallel loop  60  also passes through the corresponding switching element  32 . The illustrated switching element  32  includes a relay  68  and a machine switch  70 . The switching element  32  is designed such that the machine switch  70  is normally open, and is only closed when there is current passing though the relay  68 . In one embodiment, the switching element  32  includes an opto-coupler  72  in order to electrically isolate the dead man circuit  34  from the machine control link  30 . 
         [0030]    It should be understood that the above-described components are described in relation to the illustrated embodiment, and their description in a particular orientation would not necessarily be required in order to practice the present invention. For example, while the machine controller  28 , switching element  32 , unit select switch  62 , and current sink  66  are all described and illustrated as being within the confines of the machines  18 , some of those components could be positioned outside the machines  18 . Similarly, some of the components of the dead man circuit  34  that are illustrated as being positioned in the control center  22  could be positioned outside the control center  22  (e.g., in their own housing). 
         [0031]    In operation, the above-described components function to limit the number of machines  18  operating any a given time. Prior to operation of a machine, the dead man enable switch  38  and all unit select switches are open, and thus there is no current flowing in the dead man circuit  34 . In addition, the machine switches  70  are open, thus preventing the machine controller  28  from initiating operation of the corresponding machine  18 . 
         [0032]    Referring to  FIG. 3 , when operating a machine  18  is desired, a start command  80  is provided to the system controller  24 . The following description assumes a single machine  18  is selected, but the same process would be followed if multiple machines  18  are selected. The start command  80  can be in the form of a user selecting operation of the desired machine  18  (e.g., pressing a button), software (internal or external) initiating a programmed operation of the machine, or any other suitable start command. Upon receipt of the start command  80 , the system controller  24  selects  82  which machine  18  should be activated, and sends  84  a machine select command  82  via the communication link  26 . Upon receipt of the machine select command, the corresponding machine controller  28  closes the corresponding unit select switch  62 , which enables  86  the corresponding current sink  66 . 
         [0033]    The user then must press  88  the dead man button  42 , which closes the dead man enable switch  38 . This allows current to flow through the dead man circuit  34 . More specifically, current will flow through the parallel loop  60  in the selected machine  18 , which will close the machine switch  70  corresponding with the selected machine  18 . 
         [0034]    After the dead man circuit  34  is closed, the system controller  24  waits  90  for about 100 mSecs for the current in the dead man circuit  34  to be filtered, stabilized, and analyzed. The wait period is chosen to be sufficient time for the dead man trip  40  to function prior to movement of the machine(s)  18 . That is, the time delay allows the dead man trip  40  to determine whether too many machines  18  have been selected, which would result in tripping the dead man circuit  34  and preventing movement of any machines  18 . In this regard, the overload management system of the present invention provides a proactive overload management that is hardware based. 
         [0035]    During the wait time, the dead man trip  40  measures  92  the current in the dead man circuit  34  and compares  94  the measured current to a maximum current. At that point, a decision  96  is made whether or not the measured current exceeds the maximum current. If no, then the dead man circuit  34  remains closed, and the system controller  24  will send  98  a movement command to the machine controllers  28  after the above-referenced wait period. This will result in moving  100  the selected machine  18 . 
         [0036]    Alternatively, if the measured current is above the maximum current, then the dead man circuit  34  is opened  102  by opening the trip contact  44 , and the machines  18  are stopped  104  or prevented from moving. In this situation, the trip contact  44  is held open by the hold unit  52 , and the hold unit  52  can then be reset by the reset unit  54 , as described above. 
         [0037]    As noted above, the illustrated embodiment is designed to limit operation of no more than four machines  18  at once. As a result, if start commands are given for five machines  18 , the resulting current in the dead man circuit  34  will be 50 mA, which will cause the dead man trip  40  to open the trip contact  44  to disable the dead man circuit  34 . With no current flowing through the dead man circuit  34 , the switching elements  32  in the machines  18  will revert to their normal states, causing all of the machine switches  70  to open. This cuts communication between the machine controllers  28  and the motors  20 , thereby preventing operation of all machines  18 . 
         [0038]    When a start command is provided while some machines  18  are already moving, the same logic occurs. In this case, however, there is already current in the dead man circuit  34  (from the machines  18  that are already operating). Any additional machines  18  that are selected will then add to the current in the dead man circuit  34 . If the total number of machines  18  operating plus the numbers of machines  18  selected for operation exceed the maximum allowable, then the dead man trip  40  will open the trip contact  44 , and all machines  18  will be stopped, as described above. 
         [0039]    The above-described system provides a means for limiting the number of machines  18  being operated at the same time. The system (i.e., the dead man circuit  34 ) is purely hardware, and thus is not reliant on proper software operation. It should be understood, however, that this system can be used as a back-up to a software system for limiting operation of the machines  18 . That is, the software in the system controller  24  can be programmed such that it will not allow operation of more than the maximum number of machines  18  at the same time. If the software system operates properly, then the load management system of the dead man circuit  34  is not utilized. However, if there is a malfunction of the system software, the dead man circuit  34  will limit the number of machines  18  operating at the same time. 
         [0040]    It is also noted that the present invention is capable of not only stopping the machines when too many have been actuated, but also proactively preventing the machines from starting in the first place. In other words, it can prevent the dynamic pulse that occurs when too many machines are started before the machines are started. This is in contrast to a system that has a 3-phase circuit breaker that will only trip after the too machine have started to move, and thus doesn&#39;t avoid the start-up pulse caused by too many machines. 
         [0041]    Although the present invention has been described with reference to particular embodiments, it should be recognized that these embodiments are merely illustrative of the principles of the present invention. Those of ordinary skill in the art will appreciate that a dynamic load management system and/or method according to the present invention may be constructed and implemented in other ways and embodiments. In addition, where methods and steps described above indicate certain events occurring in a particular order, those of ordinary skill in the art having the benefit of this disclosure would recognize that the ordering of certain steps may be modified and that such modifications are in accordance with the variations of the invention. Additionally, certain of the steps may be performed concurrently in a parallel process when possible, as well as performed sequentially as described above. Accordingly, the description herein should not be read as limiting the present invention, as other embodiments also fall within the scope of the present invention.