Abstract:
A safety system for preventing crane operator injury. Two ergonomic tracks are attached on either side of the working crane. A fall transmitter is used whenever a crane operator is not on the floor. The fall transmitter has speed and travel distance governors that limit the speed and travel of certain aspects of the crane. In a further embodiment, a second fall transmitter is utilized by the second crane operator to assure that both operators are aware of and agree to any crane movement prior to commencing such movement.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority of U.S. Provisional Patent Application No. 60/710,457, filed Aug. 23, 2005 which is herein incorporated by reference. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable. 
   APPENDIX 
   Not Applicable. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to the safety of employees in elevated work positions and, more specifically, to vertical lifeline systems. 
   2. Related Art 
   An overhead bridge crane contained in a building runs on elevated beams or rails. There are two parallel beams or rails called runway beams. Perpendicular to the runway beams is the bridge or girder (also called the “crane”). The bridge, or “crane,” is connected to the runway beams by two end trucks on each end of the bridge. The end trucks can be anywhere from five feet long for a small crane to nearly twenty feet long for a long span crane. The bridge can move in either direction along the runway beams (“North-South” will be used herein to describe this “bridge travel”) via these end trucks. On the bridge is a trolley, which can move in either direction along the bridge (“East-West”). The trolley holds the working hoist, which can move Up or down (“Up-Down”); the working hoist in a bridge crane lifts and lowers the object of the work, the load. Most bridge cranes are controlled via remote control radio transmitters. The structure of bridge cranes allows 3-axis motion in the X, Y, and Z planes and thus allows full coverage of the floor to perform work. 
   When a crane operator doing work with an overhead bridge crane (a “working crane”) is more than six or seven feet above the floor, the operator is required by Occupational Health and Safety Administration (OSHA) to use fall protection equipment. Since a considerable amount of crane work is elevated, or “up,” elevated crane operators, or “fall operators,” generally wear fall protection equipment, such as a personal fall arrest system. However, many fall operators use no protection, which is a direct violation of OSHA. When protection is used, methods are often cumbersome and restrictive, and are generally a hassle. 
   In one type of personal fall arrest system, a Vertical Lifeline System, a fall operator is attached to an anchorage overhead. The system consists of a fixed anchorage, a self-retracting lifeline (SRL), and a body harness. When the fall operator moves, the fixed anchorage is no longer directly above the fall operator, creating an angle. This leads to a pendulum effect if a fall operator should fall, which is not ideal under the American National Standards Institute (ANSI) codes regarding verticality of fall restrictions. 
   A second fall arrest system, the Monorail Beam, consists of a beam located under the runway beam that swings out parallel to the runway. This method is problematic because the beam is usually located where the crane needs to work. In addition, the SRLs used move trolleys with considerable rolling resistance. Consequently, when a fall operator needs to move, that fall operator has to tug at the SRL to move the trolley along the beam, which requires significant effort. Moreover, the Monorail Beam system is quite expensive and often requires a hydraulic power supply to move it. 
   A third and more commonly used fall arrest system is comprised of a second overhead bridge crane (a second bridge with a light capacity), or “fall crane.” This fall crane is placed on the same runway beams as the working crane. Thus, the working crane and the fall crane are parallel and adjacent to each other. An anti-collision system on the working crane is needed so that the working crane and the fall crane do not accidentally collide. One or two trolleys are placed on the fall crane bridge; an SRL is connected to each trolley, and a body harness is attached to each SRL. By installing either one or two trolleys, the fall crane can be designed to support either one or two fall operators. There are various problems with this fall protection method, as described below: 
   a) It is not cost-efficient to buy and maintain a second crane (the fall crane) that does no work. Additionally, it is less efficient and more costly to have two cranes in operation (the working crane and the fall crane) instead of one. 
   b) Two transmitters are needed, one for the working crane and a second for the fall crane. This results in two transmitters to maintain and control instead of one. 
   c) Since the fall crane is always on one side or the other of the working crane, the fall crane is often in the way of the working crane. If the working crane needs to be moved, either the fall crane must first be moved out of the way, or the fall crane must be moved along with the working crane. This extra step is inefficient and may require a second crane operator in addition to the operator for the working crane. 
   d) The working crane and the fall crane often need to be positioned close to each other to get work done. In order to position the two cranes close to one another, an anti-collision override on the working crane must be activated. This requires the pushing of two buttons instead of one: the anti-collision override button and the normal move button. 
   e) Since the fall crane is always on one side or the other of the working crane, the two cranes are always separated; the greater the length of the end trucks, the greater the separation between the two cranes. As a result of this separation, a fall operator positioned by the working crane is attached to a lifeline that is not directly vertical. The angle that is created leads to a pendulum effect if a fall occurs, which is not ideal under the ANSI codes regarding verticality of fall restrictions. 
   f) If the fall crane is designed to support two fall operators (if there are two SRLs attached to the fall crane), the fall operators must work side by side on the fall crane and cannot “pass” each other (East-West) along the fall crane to work in each other&#39;s location. This restricts a fall operator&#39;s ability to get work done. The side-by-side positioning of two fall operators also creates an angle problem, leading to a pendulum effect if a fall occurs. 
   g) The trolleys have significant rolling resistance. As a result, when a fall operator wants to move East-West, that operator has to tug at the SRL to move the trolley along the bridge, which requires significant effort. 
   h) The working crane has unrestricted movement at all speeds. As a result, a fall operator can unintentionally drag himself (and another fall operator if there are two) off of the equipment. 
   i) When there are two operators “up,” there is the risk that one of the fall operators will not be in a position where he is ready for the other fall operator to move the crane. 
   For the foregoing reasons, the second overhead bridge crane method is not ideal. 
   SUMMARY OF THE INVENTION 
   A fall protection system is needed in which a working crane can be safely operated through restrictions on the working crane&#39;s speed and travel distance. At the same time, the fall operator protected by this system must be permitted to do work with as few restrictions as possible. The present invention is an improved fall protection system for crane operators in a working crane environment. 
   In the present invention, the fall system is mounted onto a working crane. The fall system will work with top running single girder working cranes, top running double girder working cranes, and under running single girder working cranes. If the existing working crane is not new, the working crane must be modernized to accommodate the fall system. 
   The working crane has two main runway beams running in one direction (designated North-South for clarity) and a bridge (and girders) running in a second direction (designated East-West for clarity) between the two runway beams. End trucks attached to both sides of the bridge are connected to the main runway beams and allow North-South bridge travel to occur. The present invention can be used for bridge travel controls that are two speeds, three speeds, four speeds, five speeds, and infinitely Variable Speed Controlled (VFD). 
   The fall system includes ergonomic tracks running in the second direction (designated East-West for ease of reference), which are attached on either side of the working crane. On a double girder working crane, the tracks are attached to each girder. On a single girder working crane, the tracks are attached to structural beams on either side of the girder (bridge). 
   Track supports running in the North-South direction are fixed to and run perpendicular to the two ergonomic tracks. A trolley runs along each track in the East-West direction. A self-retracting lifeline (SRL) is attached to each trolley; a body harness (not included in the present invention) is attached to each SRL. This setup provides fall protection for two fall operators, one on each side of the working crane. If there are two fall operators instead of one, each of the two fall operators is attached to his own track (since there are two tracks). 
   The two ergonomic tracks and multiple track supports form one unit that has the capability to move as a whole in the North-South direction; the unit does not have the capability to move in the East-West direction. 
   When the working crane needs to be moved to perform work, a fall operator generally moves with the working crane in order to remain close to the work being done. In the present invention, a fall operator has the capability to move his fall restriction with him in both the North-South and East-West directions. When the working crane moves North-South, a fall operator can move himself by moving his SRL along the ergonomic track in the North-South direction. When the working crane moves East-West, the unit comprised of the tracks and track supports moves East-West along with the working crane; thus, the fall operator does not take any action to move himself since he moves with the unit. 
   After work has been completed, a fall operator disconnects the SRL from his body harness and climbs down. 
   While operated from the floor (when there are no operators “up” and floor operators are thus operating the working crane), a floor transmitter is used. The floor transmitter can be in the form of a handheld device or consist or two or three joysticks. In order to activate the floor transmitter to move the working crane via floor mode, a master key is inserted into the transmitter. A function (hoist motion, trolley motion, or bridge motion) and a direction (up or down for the hoist, forward or reverse for the trolley, and forward or reverse for the bridge) are then selected. The crane can then be operated as a normal working crane at all speeds (stop, low, or high). 
   When operated from above the floor (when there are operators “up” and fall operators are thus operating the working crane), a fall mode is engaged, and a fall operator changes to a different radio transmitter called a fall transmitter. The fall transmitter is in the form of a handheld device. In order to use this fall transmitter to move the working crane, the master key is removed from the floor transmitter (thereby deactivating the floor transmitter) and is inserted into the fall transmitter (thereby activating the fall transmitter). When this fall transmitter is activated, a novel Safety Radio Interface System (SRIS) is also activated. 
   The SRIS consists of the floor transmitter (of the form desired), a handheld fall transmitter, and a Control Logic Module System (CLM); the SRIS may also include a safety fall transmitter for a two-man setup if so desired. 
   Once the fall transmitter and SRIS are activated, a function (hoist motion, trolley motion, or bridge motion) and a direction (up or down for the hoist, forward or reverse for the trolley, and forward or reverse for the bridge) are then selected. 
   SRIS imposes various restrictions on mobility. There are no restrictions on the Up-Down movement of the hoist; thus, the hoist can move at the following speeds: stop, low, and high. The trolley (moving East-West along the bridge) can be operated at stop or low speeds only; high speed is prevented by the system. 
   SRIS imposes two restrictions upon bridge movement via a computer logic module system (CLM). First, the bridge (moving North-South) can be operated at stop or low speeds only. Additionally, the CLM controls the travel distance of the bridge: the bridge can only travel a pre-designated maximum distance (or “range”) in either direction. This distance cannot be altered by the fall operator. A fall operator has the ability to move the bridge back and forth (North-South) as many times as the operator chooses within the pre-designated range. When the maximum travel distance is reached, the CLM causes the bridge to stop; the bridge cannot be moved any further in the same direction but can be moved back in the opposite direction within the maximum travel distance. 
   In an alternative embodiment, called a two-man safety control system, both fall operators carry radio transmitters. The first fall operator has a main fall transmitter in fall mode. The second fall transmitter has a safety fall transmitter that is activated via the pressing and holding of a push button. There are two steps required in order to activate the main fall transmitter and allow the first fall transmitter to move the working crane. First, the master key must be inserted into the main fall transmitter (as described above). Second, the second fall operator must give permission (by activating the safety fall transmitter) to the first fall operator to move the crane. Only then can the first fall operator move the working crane. Movement of the crane by the first fall transmitter is restricted to the fall mode (as described above). 
   Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a plan view from above of an embodiment of the present invention using a top running single girder working crane. 
       FIG. 2  is an elevation view from the side of an embodiment of the present invention using a top running single girder working crane. 
       FIG. 3  is an end view of an embodiment of the present invention using a top running single girder working crane. 
       FIG. 4  is a plan view from above of an embodiment of the present invention using a top running double girder working crane with a lower girder flange. 
       FIG. 5  is an elevation view from the side of an embodiment of the present invention using a top running double girder working crane with a lower girder flange. 
       FIG. 6  is an end view of an embodiment of the present invention using a top running double girder working crane with a lower girder flange. 
       FIG. 7  is a plan view from above of an embodiment of the present invention using a top running double girder working crane with no lower girder flange. 
       FIG. 8  is an elevation view from the side of an embodiment of the present invention using a top running double girder crane with no lower girder flange. 
       FIG. 9  is an end view of an embodiment of the present invention using a top running double girder working crane with no lower girder flange. 
       FIG. 10  is a plan view from above of an embodiment of the present invention using an under running single girder working crane. 
       FIG. 11  is an elevation view from the side of an embodiment of the present invention using an under running single girder working crane. 
       FIG. 12  is an end view of an embodiment of the present invention using an under running single girder working crane. 
       FIG. 13  is a flow diagram illustrating the mechanical setup of an embodiment of the present invention, including the methods by which working cranes are prepared for the fall system. 
       FIG. 14  is a flow diagram illustrating the controls setup of an embodiment of the present invention, including the possible types of floor transmitters and the methods by which the Safety Radio Interface System is installed. 
       FIG. 15  is a flow diagram illustrating the method by which the working crane supporting an embodiment of the present invention is operated from the floor when there is one fall operator, including the activation of the system and the operation of the working hoist, trolley, and bridge. 
       FIG. 16  is a flow diagram illustrating the method by which the working crane supporting an embodiment of the present invention is operated from above the floor when there is one fall operator, including the activation of the system, the operation of the working hoist, trolley, and bridge, and the restrictions placed upon the system by the Control Logic Module System. 
       FIG. 17  is a flow diagram illustrating the method by which the working crane supporting an embodiment of the present invention is operated from above the floor when there are two fall operators, including the activation of the system, the operation of the working hoist, trolley, and bridge, and the restrictions placed upon the system by the Control Logic Module System. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, preferred embodiments of the present invention will be described with references to the accompanying drawings. The description of the embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or its uses. 
   Advantageously, in the preferred invention the fall system is mounted onto the working crane. Such a setup results in no need for a separate fall crane that does no work and that gets in the way of the working crane. Moreover, the same transmitter used to operate the working crane is used to operate the fall system, which results in one less transmitter to maintain and control. Furthermore, because there is only one crane, there is no need for a fall operator to push two buttons to move a working crane and a fall crane close to each other to do work; fewer required steps leads to increased work efficiency. 
   There are four preferred embodiments of the present invention due to the fact that the fall system can be incorporated into multiple types of working cranes. The first preferred embodiment entails the use of the fall system with a top running single girder working crane, as shown in  FIGS. 1 ,  2 , and  3 . The second preferred embodiment entails the use of the fall system with a top running double girder working crane with a lower girder flange, as shown in  FIGS. 4 ,  5 , and  6 . The third preferred embodiment entails the use of the fall system with a top running double girder working crane without a lower girder flange, as shown in  FIGS. 7 ,  8 , and  9 . The fourth preferred embodiment entails the use of the fall system with an under running single girder working crane, as shown in  FIGS. 10 ,  11 , and  12 . 
   The working crane used in all four of the preferred embodiments contains common elements. First, a bridge is attached to either one or two girders  32 . Additionally, end trucks  34  are attached on both sides of the bridge; these end trucks connect the bridge to the runway beams and allow bridge travel along the runways. 
   In all four of the preferred embodiments, the working crane span is adapted to the preference of the customer and to the physical dimensions of the work area. The preferred type of hoist  52  on the working crane is a wire rope or an electric chain hoist. The preferred source voltage is 230/3/60 or 460/3/60. The preferred control voltage is 115/1/60. 
   In the accompanying drawings illustrating the structures of the four preferred embodiments ( FIGS. 1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11 ,  12 ),  40  denotes floor level generally,  42  denotes runway height,  44  denotes clear height, and  46  denotes the preferred three-inch minimum clearance between. In all end views of the preferred embodiments ( FIGS. 3 ,  6 ,  9 ,  12 ), the working hoist  52  is not shown for clarity. 
   In all four of the preferred embodiments, the fall system consists of ergonomic tracks  54  attached on either side of the working crane; these tracks  54  run in the East-West direction. Additionally, the fall system contains track supports  56  fixed to the two ergonomic tracks  54 ; these track supports  56  run in the North-South direction. Sliding control trolley conductors  58  are also utilized. A trolley runs along each track  54  in the East-West direction. The two tracks  54  and multiple track supports  56  form one unit that has the capability to move as a whole in the North-South direction; the unit does not have the capability to move in the East-West direction. An SRL  60  is attached to each trolley; a body harness (not included in the present invention) is attached to each SRL  60 . 
   The first preferred embodiment (utilizing a top running single girder crane, as shown in  FIGS. 1 ,  2 , and  3 ) is distinct from other preferred embodiments in that, because there is only one girder  32 , the ergonomic tracks  54  are attached to structural beams on either side of the girder  32 . 
   The second preferred embodiment (utilizing a top running double girder working crane with a lower girder flange, as shown in  FIGS. 4 ,  5 , and  6 ) is distinct from other preferred embodiments in the following ways. First, because there are two girders  32 , each track  54  is attached to the underside  82  of a girder  32 . Second, this embodiment utilizes a structural beam or fabricated box beam with lower flange  80 . 
   The third preferred embodiment (utilizing a top running double girder working crane without a lower girder flange, as shown in  FIGS. 7 ,  8 , and  9 ) is distinct from other preferred embodiments in the following ways. First, because there are two girders  32 , each track  54  is attached to the underside  82  of a girder  32 . Second, it utilizes a fabricated box beam with no lower flange  90 , as well as a fabricated bracket welded to a girder web plate  92 . 
   The fourth preferred embodiment (utilizing an under running single girder working crane, as shown in  FIGS. 10 ,  11 , and  12 ) is distinct from other preferred embodiments in that, because there is only one girder  32 , the tracks  54  are attached to structural beams on either side of the girder  32 . 
     FIG. 13  illustrates the mechanical setup of the fall system  150 . If the working crane in place is an already-existing, older crane  154 , the working crane must be modernized  156  to support the fall system. If the modernized working crane is a single girder crane  158 ,  160 , two ergonomic tracks  54  must be installed  162 , and self-retracting lifelines (SRLs) must then be installed  164 . If the modernized working crane is a double girder crane  165 ,  166 , tracks must be installed as follows. If only one track is desired (if there will only be one fall operator)  172 , one ergonomic track  54  must be installed  174 , and one SRL  60  must then be installed  176 . If two tracks are desired (if there will be two fall operators)  167 ,  168 , two ergonomic tracks  54  must be installed  169 , and two SRLs  60  must then be installed  170 . 
   If the working crane in place is a new crane with no need for modernization to support the fall system  152 ,  178 , the following installations must occur. If the working crane is a single girder crane  180 ,  182 , two ergonomic tracks  54  must be installed  184 , and self-retracting lifelines (SRLs) must then be installed  186 . If the working crane is a double girder crane,  188 ,  190 , ergonomic tracks  54  must be installed as follows. If only one track is desired (if there will only be one fall operator)  194 , one ergonomic track  54  must be installed  196 , and one SRL  60  must then be installed  198 . If two tracks are desired (if there will be two fall operators)  192 ,  200 , two ergonomic tracks  54  must be installed  202 , and two SRLs  60  must then be installed  204 . 
     FIG. 14  illustrates the controls setup of the fall system  2 . If the working crane is new  252 ,  254 , a floor transmitter must be selected  256 . There are three options for a floor transmitter: a hand held version  258 , two joy sticks  260 , or three joy sticks  262 . Additionally, the Safety Radio Interface System (SRIS) must be installed  264 . The SRIS consists of the floor transmitter (of the form desired), a handheld fall transmitter, and a Control Logic Module System (CLM); the SRIS may also include a safety fall transmitter for a two-man setup if so desired. If a two-man control setup is desired  266 ,  268 , such a system must then be installed  270  (if not needed  272 , there is no need for an installation  274 ) 
   If the working crane is a modernized version of an existing working crane  276 ,  278 , a type of floor transmitter must also be selected  280 . As with a new working crane, there are three options for a floor transmitter with a modernized working crane: a hand held version  282 , two joy sticks  284 , or three joy sticks  286 . Additionally, the SRIS, containing the same elements as described above, must be installed  288 . If a two-man control setup is desired  290 ,  292 , such a system must then be installed  194  (if not needed  296 , there is no need for an installation  298 ). 
   Movement of the fall operator is simplistic and efficient in all four of the preferred embodiments. A fall operator has the capability to move his fall restriction with him in both the North-South and the East-West directions. As a result, the fall restriction is always directly above the fall operator, and there is thus no pendulum effect in the case of a fall. 
   When the working crane moves East-West, a fall operator can remain positioned by the working crane by moving his SRL  60  along his ergonomic track  54  in the East-West direction. Rolling resistance of the trolley is minimized due to the ergonomic nature of the tracks  54 . Consequently, a fall operator does not have to tug at his SRL  60  to move the trolley, resulting in freer movement of the trolley. 
   When the working crane moves North-South, the unit comprised of the tracks  54  and track supports  56  moves North-South with the working crane; the fall operator and his fall restriction thus stay with the working crane without any action on the fall operator&#39;s part. Increased efficiency and ease result from this automatic movement of the fall system. 
   The setup of all preferred embodiments allows fall protection for two fall operators, one on each side of the working crane. This setup is advantageous because two fall operators no longer have to work side by side. Two fall operators can move with full freedom along the tracks  54  (East-West) while both attached to the system. Consequently, there are fewer restrictions on a fall operator&#39;s ability to get work done. Furthermore, having only one fall operator on each track  54  eliminates the angle problem of having two workers attached side by side. Thus, no pendulum effect is created in the case of a fall, which is ideal under the American National Standards Institute (ANSI) codes regarding verticality of fall restrictions. 
   Operation of the present invention is safely restricted and efficient. In addition to the basic structural elements (ergonomic tracks, track supports, sliding control trolley conductors, trolleys, and SRLs), all four preferred embodiments include a crane control panel  70  and an SRIS  72 . The SRIS  72  imposes various restrictions on mobility when the working crane is operated by fall operators (is in fall mode) but imposes no restrictions when the working crane is operated by floor transmitters. Consequently, the working crane is a fully functional crane (can be operated at all speeds) for floor operators and is a fully functional but safely restricted crane for fall operators. SRIS-imposed restrictions include maximum travel distance of the bridge and maximum speed of the bridge and the trolley; these restrictions are controlled via a computer logic module system (CLM)). 
   Advantageously, the speed restrictions and bridge travel distance restrictions greatly diminish the chance that a fall operator will unintentionally drag himself (or another fall operator if there are two) off of the equipment. Additionally, due to the travel distance restrictions, there is no need for an anti-collision system to prevent collisions between the working crane and the ergonomic tracks  54 . (If additional, neighboring cranes are in the area of the working crane, however, it is preferred that an anti-collision system be installed on the neighboring crane for the safety of the fall operator.) 
     FIG. 15  illustrates how the working crane is operated from the floor (when there are no operators “up” and floor operators are thus operating the working crane)  350 . There are no SRIS-imposed restrictions on mobility when floor operators are operating the working crane. In order to operate the working crane in this arrangement, a floor radio transmitter is first selected  350 . A master key is then inserted into the floor transmitter  352 . If a master key is currently in the fall transmitter  354 , the master key must be removed from the fall transmitter and taken down to the floor level  356 , and then inserted into the floor transmitter  352 . Once the master key is inserted into the floor transmitter  358 , the floor transmitter is activated  360 . 
   Next, a function is selected by the floor operator  362 . If hoist motion is selected  364 , the floor operator can select upward motion  366  or downward motion  376 . If upward motion is selected  366 , the floor operator can select one of the following speeds  368 : stop  370 , low  372 , or high  374 . Similarly, if downward motion is selected  378 , the floor operator can select one of the following speeds  378 : stop  380 , low  382 , or high  384 . 
   If trolley motion is selected  386 , the floor operator can select forward motion  388  or reverse motion  398 . If forward motion is selected  388 , the floor operator can select one of the following speeds  390 : stop  392 , low  394 , or high  396 . Similarly, if reverse motion is selected  398 , the floor operator can select one of the following speeds  400 : stop  402 , low  404 , or high  406 . 
   If bridge motion  408  is selected by the floor operator, the floor operator can then select forward motion  410  or reverse motion  420 . If forward motion is selected  410 , the floor operator can select one of the following speeds  412 : stop  414 , low  416 , or high  418 . Similarly, if reverse motion is selected  420 , the floor operator can select one of the following speeds  422 : stop  424 , low  426 , or high  428 . 
     FIG. 16  illustrates how the working crane is operated from above the floor by one operator (when there is one operator “up” and one fall operator is thus operating the working crane). There are SRIS-imposed restrictions on mobility when one fall operator is operating the working crane. In order to operate the working crane in this arrangement a fall radio transmitter is first selected  4 . A master key is then inserted into the fall transmitter  454 . If a master key is currently in the floor transmitter  454 , the master key must be removed from the floor transmitter and taken up  456 , and then inserted into the fall transmitter  454 . Once the master key is inserted into the fall transmitter  458 , the fall transmitter is activated  460 . 
   Next, a function is selected by the fall operator  462 . If hoist motion is selected  464 , the floor operator can select upward motion  466  or downward motion  476 . If upward motion is selected  466 , the floor operator can select one of the following speeds  468 : stop  470 , low  472 , or high  474 . Similarly, if downward motion is selected  476 , the floor operator can select one of the following speeds  478 : stop  480 , low  482 , or high  484  (there are no SRIS-imposed restrictions on the Up-Down movement of the hoist). 
   If trolley motion is selected  486 , the floor operator can select forward motion  488  or reverse motion  496 . If forward motion is selected  488 , the floor operator can select one of the following speeds  490 : stop  492  or low  494  only (high speed is not allowed by the system). Similarly, if reverse motion is selected  496 , the floor operator can select one of the following speeds  498 : stop  500  or low  502  only (high speed is not allowed). 
   If bridge motion is selected by the fall operator  504 , the fall operator can then select forward motion  506  or reverse motion  508 . Once the motion direction has been selected, the CLM governs the speed  510 , allowing the trolley to move either at forward low speed  512  or reverse low speed  522  only (high speed is not allowed by the system). 
   SRIS imposes maximum bridge travel distance restrictions via CLM. The bridge can only travel a pre-designated maximum distance (or “range”) in either direction. This distance cannot be altered by the fall operator. A fall operator has the ability to move the bridge back and forth (North-South) as many times as the fall operator chooses within the pre-designated range. When the maximum travel distance is reached, the CLM causes the bridge to stop; the bridge cannot be moved any further in the same direction but can be moved back in the opposite direction within the maximum travel distance. 
   This process operates as follows. If the forward direction for bridge motion has been chosen  506 , the CLM determines whether the bridge has already traveled the maximum forward distance  514 . If the bridge has already traveled the maximum forward distance  518 , the bridge stops  520 . If it has not  516 , the bridge continues at forward slow speed  512  until the CLM judges that maximum distance has been reached  514 , upon which the bridge stops  520 . 
   If the reverse direction for bridge motion has been chosen  508 , the CLM determines whether the bridge has already traveled the maximum reverse distance  524 . If the bridge has already traveled the maximum reverse distance  528 , the bridge stops  530 . If it has not  526 , the bridge continues at reverse slow speed  522  until the CLM judges that maximum distance has been reached  524 , upon which the bridge stops  530 . 
     FIG. 17  illustrates how the working crane is operated from above the floor when there are two operators “up”  5 . This alternative embodiment, called a two-man safety control system, can be used with any of the four preferred embodiments described above. In this alternative embodiment, both fall operators carry radio transmitters. The first fall operator has a main fall transmitter in fall mode. The second fall transmitter has a safety fall transmitter that is activated via the pressing and holding of a push button. 
   In order to operate the working crane in this arrangement, a two-man radio transmitter is first selected  550  and then turned on  552  by the insertion of the master key into the transmitter; once the radio has been turned on  554 , the transmitter has been activated  556 . Next, the second fall operator must give permission (by activating the safety fall transmitter) to the first fall operator to move the crane  558 . This permission indicates that the second operator is clear, ready, and safe for the first operator to take control and move the working crane. Such a safeguard assures that both fall operators are aware of and agree to any working crane movement before the movement commences. The CLM processes  564  a “yes” permission signal  562 ,  568  or a “no” permission signal  560 ,  566 . 
   If the first fall transmitter has selected bridge motion  570 , and if the first fall operator has received the second fall operator&#39;s permission  572 ,  578 , the first fall operator has the ability to move the working crane via bridge motion  580 . If the first fall transmitter has selected bridge motion  570 , and if the first fall operator has not received the second fall operator&#39;s permission  572 ,  574 , the first fall operator does not have the ability to move the working crane via bridge motion  576 . 
   Movement of the crane by the first fall operator in this two-man safety control system is restricted to the fall mode (and thus subject to speed and travel distance limitations). If bridge motion is selected by the first fall operator  570 ,  580 , the first fall operator can then select forward motion  582  or reverse motion  584 . Once the motion direction has been selected, the CLM governs the speed  586 , allowing the trolley to move either at forward low speed  588  or reverse low speed  598  only (high speed is not allowed by the system). 
   If the forward direction for bridge motion has been chosen  582  by the first fall operator, the CLM determines whether the bridge has already traveled the maximum forward distance  590 . If the bridge has already traveled the maximum forward distance  594 , the bridge stops  596 . If it has not  592 , the bridge continues at forward slow speed  588  until the CLM judges that maximum distance has been reached  590 , upon which the bridge stops  596 . 
   If the reverse direction for bridge motion has been chosen  584  by the first fall operator, the CLM determines whether the bridge has already traveled the maximum reverse distance  600 . If the bridge has already traveled the maximum reverse distance  604 , the bridge stops  606 . If it has not  602 , the bridge continues at reverse slow speed  598  until the CLM judges that maximum distance has been reached  600 , upon which the bridge stops  606 . In this way, one alternative embodiment of the present invention provides a safely restricted and efficient means for the working crane to be moved when two operators are “up.” 
   As various modifications could be made to the exemplary embodiments, as described above with reference to the corresponding illustrations, without departing from the scope of the invention, it is intended that all matter contained in the foregoing description and shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. For example, the directional terms “North-South” for one orientation and “East-West” for another orientation are illustrative and not literally North-South and East-West. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments but should be defined only in accordance with the following claims appended hereto and their equivalents.