Patent Abstract:
A balancer hoist has an electric servomotor driving irreversible gearing in turn driving a hoist chain drive. A float mode and a manual mode are provided using two independent load sensors for sensing the load weight and force applied to a control grip. A traversing control is produced by a tractor carriage rolling on an overhead rail connected to a trolley also traveling on the rail and supported on upper hoist assembly. A load sensor interconnects the tractor carriage and upon hoist assembly to sense forces created by an operator pulling on the chain, which are used to control an electric motor on the tractor carriage driving a pinion gear engaged with a gear rack on the overhead rail to positively drive the carriage, trolley and upper hoist assembly along the rail. A stationary dual hoist system is also described in which two hoist assemblies are interconnected by a chain and sprockets to provide synchronized operation.

Full Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of provisional patent application Ser. No. 60/663,305, filed on Mar. 18, 2005. 
   This application is a division of utility patent application Ser. No. 11/385,011 filed Mar. 20, 2006 now U.S. Pat. No. 7,467,723. 

   BACKGROUND OF THE INVENTION 
   Balancing hoists have long been known in which a drum has a length of cable wound and unwound thereon as the drum is rotated in either direction to position a load held by the cable. This arrangement has utilized pneumatically operated hoists which use regulated air pressure acting on a piston to cause cable wind up or pay out by rotation of the drum. See U.S. Pat. No. 3,428,298 for a detailed description of this type of hoist. The load can be raised or lowered by the operator by exerting a low level force on the suspended load which increases or decreases the air pressure acting on the piston slightly, which pressure change is made up by a regulator to lower or raise the load accordingly. 
   The limited stroke of the piston limits the cable travel that can be obtained, and thus electrical motor driven balancer hoist have been developed, as described in U.S. Pat. Nos. 3,921,959 and 4,807,767. 
   The servo motor typically drives a planetary reduction gear, the output of which drives the cable wind up drum. 
   Since the cable is elastically stretchable to a significant degree, it has considerable stored energy when heavily loaded. 
   If the cable breaks, a hazard can be created by whipping of the cable caused by release of the stored energy when the cable breaks or when there is some other failure. Emergency brakes have been employed to prevent rapid unwinding of the cable in this situation. 
   The mass of the planetary gearing also increases the momentum of the movable components when winding or unwinding is underway. The control of the servo motor is made more complicated by the cable stretch and the momentum of the rotating components, creating complex dynamics, particularly at the high speeds which the electric servo motor drive systems operate. 
   The cable must always be maintained in tension during raising and lowering operation of the hoist in order to avoid loose turns in the cable windings on the drum leading to tangling of the windings, interfering with later unwinding. Sensors and complicated software are required to insure that this does not occur. 
   Thus, the use of a chain in balancing hoists would be preferable to eliminate difficulties in winding of a cable and the hazards associated with cable stretching. The use of a chain in a balancer hoist is shown in U.S. Pat. No. 3,921,959. However, the mass of a chain wound on a drum is relatively great, and when combined with the mass of a planetary gear set, this affects the response of an electric motor driven balancer hoist. 
   In some electric motor driven balancer hoists, load sensors sense a change in the load on the cable or chain to cause the electric motor to drive a drum to raise or lower the cable or chain balance a load in “float” mode. 
   The weight of an operator&#39;s hand can upset the “float” balance, since the load sensor will react to removal of the operator&#39;s hand from the handle. 
   Alternatively, manipulation of a handle or grip connected to the cable causes the motor to selectively drive the motor so as to raise or lower the load at a rate proportional to an up or down force applied by the operator to the grip. 
   Automatic controls can also execute raising or lowering motions to programmed stops as when repetitive motion cycles occur. 
   Such self balancing hoists have been mounted on trolleys traversed along an overhead aluminum rail track system. In order to assist movement of the trolleys, pulling on the cable by the operator in a given direction is sensed by a power cable angle sensor and powered driving of the trolley in that direction is created in response to sensing such cable pull. The cable angle sensor would be problematic with a chain, and has other limitations. 
   Also, trolleys have in the past been driven by friction wheels engaging a smooth surface on the aluminum rail. However, friction wheel slippage can sometimes occur especially under heavy loads, which slippage upsets the accurate functioning of the control system, as a commanded movement of the trolley may not occur if such slippage is encountered. A hoist utilizing a chain wound up on a drum would be especially troublesome. 
   It may be desirable to alternatively allow a free wheeling manually induced movement of the trolley, which has not heretofore been provided in a powered  21  trolley system. 
   Another application of pneumatic balancing hoists is the combining of two such hoists to lift a common load by synchronizing the motion of the two cables as described in U.S. Pat. No. 5,593,138. Again, the problems of improper cable winding may encountered with a lift cable and lift travel is limited by the relative short piston strokes as a practical matter. 
   It is an object of the present invention to provide an electrically powered balancer hoist using a chain which has a minimum mass of the components rotated by the electrical motor to allow the use of a chain while still providing good performance. 
   It is a further object of the present invention to provide an electric motor drive chain hoist with an automatic float mode as well as manual mode using a handle grip in which the operator&#39;s hand on the handle does not affect the float mode. 
   It is another object of the present invention which incorporates powered, sensor controlled trolley movement which is accurate and more reliable, and selectively allows free wheeling of the trolley. 
   It is a further object to provide a double hoist system using a servo motor drive and hoist chain lift. 
   SUMMARY OF THE INVENTION 
   The present invention comprises improvement to a hoist which utilizes a chain to support the load, the chain positively driven by an electric servo motor through a low mass self locking worm gear drive which holds the supported load whenever the motor is denergized. The chain is not wound up onto a drum but driven linearly by a positive rotary drive hub, the chain optionally able to be routed into a collection receptacle. The use of a hoist chain eliminates the stored energy problem of cable hoists, as a chain does not stretch appreciably compared to a cable, and the low mass of a worm gear drive minimizes the momentum of the rotated components to provide high performance of the balancer function. This avoids the disadvantages of a cable hoist, such as the need for sophisticated control over winding and unwinding of a flexible cable on a drum, the hazards of stored energy in a stretched cable, and the other disadvantages described. 
   Two load sensors are used in the hoist up-down control, held in a control box supported on the lower end of the chain. The # 1  load cell is connected between separate upper and lower load shafts passing through the control box, the lower load shaft connected to the load hook or eye to generate signals corresponding to the weight of the load signals these used to drive the load up or down when the operator directly pulls up or presses down on the load attached to the hook or eye. 
   The # 2  load sensor is used when the hoist control system is switched to a manual control as by activation of a push button switch on the control box. A handle grip is mounted to be slidable on the lower load shaft and connected via the # 2  load sensor to the upper load shaft. The # 2  load sensor creates signals in response to up or down pressure exerted on the control grip by the user causing up or down hoist operation in correspondence to up or down force applied to the grip. Forces applied to the grip do not affect the # 1  load sensor since the # 1  load sensor is connected below the upper connection point of the # 2  load sensor support, and since the handle is slidable on the lower load shaft so as to prevent any possible effects on the system if the grip is held or released when the hoist controls are set to the balance mode. 
   To improve performance of the trolley drive system, steel gear rack sections are clamped onto standard overhead rails and engaged with a pinion gear driven by electric motor powered tractor carriage connected to a hoist trolley. This creates a positive drive for powered positioning of the hoist trolley along an overhead rail; 
   The pinion gear reaction pushes an engaged gear rack more tightly against the rail surface to insure retention of the gear rack on the overhead rail. 
   The pinion gear is mounted on the tractor carriage which is connected to the hoist trolley which is supported on wheels on the rail for rolling movement along the rail. The hoist assembly is supported on the trolley so as to allow relative movement thereon. The hoist assembly is connected to the tractor carriage by a load sensor which senses the force developed when an operator pulls on the hoist chain to provide a control signal such that the hoist is automatically pulled horizontally in the direction desired by the operator by controlled activation of the drive motor. A two axis sensor allows movement in a second orthogonal direction. 
   In an alternate embodiment, the pinion can be declutched to allow free movement of the trolley, and an encoder is provided to keep track of the trolley movement during free movement thereof. 
   A tandem combination of two hoists is created by connecting two chain sprockets to the worm wheel of each drive to insure synchronized rotation of both chain drive motors. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a pictorial view of a hoist system and supporting modified overhead according to the present invention. 
       FIG. 2  is an enlarged pictorial view of a hoist upper assembly and trolley tractor drive components included in the hoist system shown in  FIG. 1  and a portion of an associated overhead rail. 
       FIG. 2A  is a pictorial view of modified form of the trolley tractor drive components. 
       FIG. 3  is a further enlarged pictorial view of certain components of the upper hoist assembly shown in  FIG. 2 . 
       FIG. 3A  is an enlarged pictorial view of the chain drive hub shown in  FIG. 3 . 
       FIG. 4  is an enlarged pictorial view of the control box and manual control grip included in the hoist system shown in  FIG. 1 . 
       FIG. 5  is an enlarged pictorial view of some of the internal components of the control box and grip shown in  FIG. 4 . 
       FIG. 6  is an enlarged pictorial view of an overhead track section and attached gear rack for the hoist trolley drive shown in  FIGS. 1 and 2 . 
       FIG. 7  is a pictorial view of a stationary dual hoist system according to the invention. 
       FIG. 8  is a pictorial view of the major internal components of the dual hoist system shown in  FIG. 7 . 
       FIG. 9  is a diagram of a two axis sensor arrangement for a traversing hoist system. 
       FIG. 9A  is rotated pictorial view of the two axis sensor arrangement shown in  FIG. 9 . 
       FIG. 9B  is a fragmentary portion of the two axis sensor shown in  FIGS. 9 and 9A . 
       FIG. 9C  is a pictorial view of the two axis sensor and associated hoist assembly components. 
       FIG. 10  is a diagrammatic representation of a cross rail arrangement enabling movement of the rail in an orthogonal direction to the rail. 
       FIG. 11  is a pictorial view of a hoist assembly incorporating the two axis sensor of  FIG. 9 . 
   

   DETAILED DESCRIPTION 
   In the following detailed description, certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 USC 112, but it is to be understood that the same is not intended to be limiting and should not be so construed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims. 
   Referring to the drawings and particularly  FIG. 1 , a hoist system  10  according to the present invention includes an upper hoist assembly  12  supported on a trolley  14  able to be traversed along an overhead rail  16  by a trolley tractor drive  18  pulling its upper hoist assembly  12  when activated. 
   A hoist chain  20  is driven up and down by a chain drive arrangement in the upper hoist assembly  12 , described below. The hoist chain  20  is connected to a lifting  18  eye  22  on which the load  24  is hung. 
   A control grip  28  extends below the control box  26 . 
   Two alternately selected basic control modes may be provided. In the first mode, a “float” mode may be provided in which the weight of the load is held stationary and up or down movement of the load  24  is produced by lifting or downwardly pushing on the load  24  itself to cause up or down driving of the chain  20  to raise or lower the load  24  in response to the forces applied to the load  24 . 
   In the second or manual mode, upward pulling or downward pushing on the grip  28  caused up or down driving of the hoist chain  20  and thus of the load  24  at a rate and in a direction corresponding to the magnitude and direction of the forces exerted on the load  24  or grip  28 . 
   The signals generated by components in the control box  26  are transmitted to the hoist controls  29 , which may be comprised of a suitably programmed industrial controller as is well known in the art, which in turn controls activation of the hoist motor  25 . 
     FIGS. 2 and 3  show further details of the upper hoist assembly  12 . 
   An electric servo motor  25  is enclosed within housing  23  which drives right angle gearing here comprising a worm gear  30  irreversibly engaged with a worm wheel  32 , which is connected to a shaft  34 , on which is affixed a chain driving hub  36  of a commercially available type which drives the chain  20  in either direction.  FIG. 3A  shows the hub  36  has a series of cavities  37 A,  37 B in which successive chain links are received to create a positive driving connection to the chain  20 . The upwardly driven chain  20  can be collected in a receptacle  38 , and when downwardly driven, chain is advanced out of the receptacle  38 . Since the chain  20  is not wound up on a drum, the collected segment of the hoist chain  20  in the receptacle  38  is not driven by the motor  25  and thus its weight does not affect the performance of hoist. 
   It is noted that other types of electric motors can be used, other than an electric servo motor, such as a VFD motor. 
   The upper hoist assembly  12  also includes a trolley support piece  40 , having linear bearings  42  affixed thereto engaged with a bearing way  44  of the trolley  14 . An upright web  46  supports two pairs of trolley wheels  48 . 
   The trolley wheels  48  roll along rail tracks  50  formed in the conventional overhead rail  16 . 
   The tractor drive carriage  18  is connected to the trolley  14  by links  52 . The tractor carriage  18  includes an electric servo motor  19  driving a pinion gear  54  by means of a worm gear  55  and worm wheel  57  engaged with a steel gear rack  56 . 
   The tractor carriage  18  includes a central plate  21  mounting tractor carriage wheels  48 A rolling on rail tracks  50 . The gear rack  56  is held against the underside of one of the tracks  50  of rail  16  by clamping plates  58  affixed to the side of the gear rack  56  by bolts  60  threaded into a hole in the gear rack  56  and into retainer blocks  62  in T slots in the side of the rail  16  ( FIG. 6 ). The reaction to driving by the pinion gear  54  tends to force the gear rack  56  more tightly against the underside of one track  50  of the rail  16  to be quite securely held against the same. Conventional existing aluminum rails can be quickly and easily modified in this way. 
   A load sensor  64  and an orthogonally arranged pair of yokes  66 ,  68  interconnects the upper hoist assembly  12  to the trolley  14  which in turn is connected to the tractor carriage  18  via links  52  connected thereto. When an operator pulls on the chain  20  in either direction, the resultant compressive or tensile load exerted on the load sensor  64  is detected, and the tractor carriage  18  is positively driven by motor  19  so as to null the signal generated by load sensor  64  to controllably move the upper hoist assembly  12  in either direction at a rate corresponding to the magnitude of the pull sensed by load sensor  64 . 
   The electric servo motor  19  is activated in a direction and at a rate tending to null the load sensor signals, and thus positively drive the tractor carriage  18  and upper hoist assembly  12  through worm gear  55  and worm wheel  57  along the rail  16  until the operator determines the desired location has been reached and discontinues pulling on the hoist chain  20 . 
     FIG. 2A  shows an alternate form of the tractor drive carriage  18 A, in which an electrically operated clutch  51  interposed between the pinion  54  and the drive components  55 ,  57  is included to allow free rolling of the tractor drive carriage  18 A along the rail  16 . An encoder  53  driven by a pinion gear  54 A engaging the gear rack  56  generates signals corresponding to the linear displacement of the tractor carriage  18 A, which allows the position of the tractor carriage  18 A to be monitored during free motion of the tractor carriage  18 A. 
     FIGS. 4 and 5  show further details concerning the control box  26  and control grip  28 . The hoist chain  20  is connected to an upper shaft  70  also connected to the top  27  of the control box  26 . 
   The upper shaft  70  is connected to a lower shaft  72  by an intermediate # 1  load sensor  74 . 
   The lower shaft  72  is threaded to a lifting eye  22  (or hook) on which the load  24  may be hung. Thus, the load sensor  74  generates electrical signals corresponding to the weight of the load  24 . These signals are transmitted via a flexible cable assembly  70  connected by means of a suitable terminal block  23  in the control box  26  mounted to a mounting plate  76  within the control box  26  to a flex cable assembly  78  ( FIG. 1 ) leading to the upper hoist assembly  12 . A programmable industrial controller may be used for the hoist controls  29  of a well known type to cause desired preprogrammed responses to inputs from control buttons  80 A,  80 B and associated switches in the control box (not shown). An emergency stop button  82  is also provided to enable complete stoppage of the servo motor  25 . 
   A # 2  load sensor  84  is also provided which is connected on one side to the upper shaft  70  via a self aligning connection  86  and on the other side to the control grip  28  via another self aligning connection  88  and bracket  90  attached to the top of the grip  28 . The control grip  28  slidably receives the lower shaft  72  which passes through the same. 
   The # 2  load sensor  84  thus only senses the forces exerted on the control grip  28  and is uninfluenced by the weight of the load, while the # 1  load sensor  74  is not influenced by the forces exerted on the grip  28 . 
   Many modes of operation are possible by suitable programming of the hoist controls. The basic modes of operation includes a “float” mode, in which the weight of the load  24  is just balanced by the hoist drive. That is, lifting or pushing down on the load  24  directly, as is done in final positioning of a load, will cause the chain  20  to be driven up or down by activation of the servo motor  25  so as to allow positioning of the load  24  in that manner. This mode may be set by a programmed event, such as by pushing the lower button  80 B briefly. 
   A “manual” mode may be selected as by pushing the upper control button  80 A. In this mode, the hoist chain  20  will be driven up if the grip  28  is pulled up, and will be driven down if the grip  28  is pushed down, at rates corresponding to the level to the level of the force exerted on the grip  28 . The load  24  is held by the irreversible engagement of the worm gear  30  and worm wheel  32  if no force is exerted on the grip  28 . 
   Upper and lower limits may be optionally preset by suitable programming of the hoist controller  29 , i.e. the load  24  driven to an upper limit by controlling activation of the servo motor  25  by pulling the grip  28  upward in the manual mode, and the upper button  82 A depressed and held until a light  86 A flashes. 
   A lower limit is set by pushing down on the grip  28  until a desired lower limit is reached, and programmed in by holding lower control button  80 B until light  86 B flashes. 
   Other control features could be programmed into the controller  29 . 
     FIGS. 7 and 8  show a stationary double hoist according to the invention. 
   In this embodiment, two spaced apart hoist assemblies  88 A,  88 B are mounted on supporting column  90  connected by a cross beam  94 . 
   An electric servo motor  92 A,  92 B is included in each hoist assembly  88   a ,  88 B driving a respective worm gear  96 A,  96 B in turn irreversibly engaged with a respective worm wheel  98 A,  98 B mounted on a respective cross shaft  100 A,  100 B. 
   Each cross shaft  100 A,  100 B has a chain drive hub  102 A,  102 B affixed thereto engaged with a respective one of the two hoist chains  104 A,  104 B. 
   A synchronizing double chain  106 A,  106 B engage both sprocket pairs  108 A,  108 B affixed to respective cross shafts  100 A,  100 B. This insures equal movements of the chains  104 A,  104 B. A chain tensioner  110  can be provided, mounted to cross beam  94 . 
   A pair of hanger plates  112 A,  112 B can be utilized to support the hoist assemblies  88 A,  88 B on the cross beam  94 . 
   A single electric motor  92 A may be used to drive both chain drive hubs  102 A,  102 B via the double chain  106 A,  106 B. 
     FIGS. 9-9C  show a two axis chain pull sensor  114  mounted in a housing  23 . 
   A tube  116  is held and restrained at its upper end by a mounting comprising of two adjustable clamp collars  134 A,  134 B on either side of a bracket  136 . A clearance C is set so that the tube  116  is constrained only by load sensor rods described below when the hoist chain  20  is pulled. One axis is aligned with the rail  16 , the other in the direction of bridge rails  16 A ( FIG. 10 ) supporting the ends of the rail  16  for movement of the hoist assembly  16  along a direction normal to the rail  16 . 
   An anti-rotation screw  138  is threaded into the upper collar  134 A through a slot  140  in the bracket  136 . 
   The tube  116  receives the hoist chain  20  which passes through to the chain drive hub  36  aligned so that the chain  20  does not normally exert any pressure on the tube  116 . When the hoist chain  20  is pulled in the direction of either axis, this causes force to be applied in either direction to a respective load sensor  124 A,  124 B. 
   The tube  116  has a pair of spaced plates  118  attached which receive self aligning eye connections  120 A, B aligned along each orthogonal axis connecting a respective rod  122 A, B to load sensor  124 A,  124 B. A second rod  126 A,  126 B is held by a fixed mounting block  132 A, B receiving another self aligning pivot connection  128 A,  128 B. The signals generated by load sensors  124 A, B are sent to the hoist controls  29  which causes activation of respective tractor drives  18 A,  130 A,  130 B to drive the hoist assembly  12  along rail  16  or rails  16 A to position the hoist assembly  12  at points along either axis. 
     FIG. 11  shows an upper hoist assembly  12 A in which the tractor trolley drive and chain drive are both contained in the housing  23 A. the tractor drive includes a clutch-pinion gear assembly  144  driven by a servo motor (not shown in  FIG. 11 ) engaged with the gear rack  56 . An encoder second pinion gear assembly  146  includes a pinion gear  54 A and encoder  53 A. 
   An industrial controller comprising the hoist control  29  is also shown. The chain drive includes an electric servo motor  25  driving irreversible right angle gearing unit  148  incorporating the worm gear and worm wheel (not shown in  FIG. 11 ).

Technology Classification (CPC): 1