Abstract:
The present invention is an anti fall device for use with scissor type mechanically actuated lifting devices. The anti fall device comprises a a slave safety hydraulic cylinder capable of supporting a lifting device upon failure of a drive assembly thereby arresting descent of the lifting device when the lifting device is normally stationary or moving upwardly and a drive assembly of the lifting device fails and the lifting device begins to descend uncontrollably. The hydraulic cylinder includes a one way check valve for preventing reverse hydraulic fluid flow upon uncontrolled descent of the lifting device thereby arresting movement of the hydraulic cylinder and arresting descent of the lifting device. The invention also includes an hydraulic velocity fuse in fluid communication with the hydraulic cylinder. The velocity fuse is triggered at a preselected fluid flow rate for controllably lowering the lifting device.

Description:
FIELD OF THE INVENTION 
   The present invention relates to lift safety devices and more particularly relates to lift anti fall devices. 
   BACKGROUND OF THE INVENTION 
   Lifting devices which are mechanically or hydraulically actuated, are used in many different industries for raising and lowering components for assembly operations and the like. There are a number of different lift designs, however, scissor type lifts are one of the most frequently used. Scissor lifts are usually actuated by either hydraulic cylinders or mechanical screw drives. 
   Hydraulically actuated and/or mechanically actuated scissor lifts are used extensively in the automotive industry, particularly on automotive assembly lines. By way of example only, in this patent, we will describe the anti fall device which is the subject matter of this patent used in association with a mechanically actuated scissor lift. 
   Vehicles are often assembled on a platform which can be raised or lowered, for the purpose of assembly and mounting of various components onto the vehicle as it progresses down the assembly line. The automotive industry is extremely concerned about safety. An uncontrolled descent of a scissor lift could present a substantial safety hazard to workers that are situated in and around the scissor lift when for example, installing componentry on the vehicle. It is desirable to have safety devices which, upon failure of the drive mechanism of the lift, would prevent uncontrolled descent of the scissor lift platform, in order to minimize and/or prevent injury to personnel. 
   Currently, the specifications which deal with the safety aspect of scissor lifts include ANSI Specification MH 29.1 Section 8.1.2 which calls for a rate of descent protection, wherein the descent of the lift is promptly arrested or the rate of descent limited to a speed not to exceed the greater of 4 times the normal down speed or 30 feet per minute when fully loaded. 
   General Motors also have their own internal specification, GMSC 1-99, Section 2.3.13 which calls for an anti fall safety device which senses an over speed condition and arrests the dropping of the scissor lift unit within two inches of travel from the point of detection. 
   The present invention an anti fall device to be used in association with lifting devices, and particularly mechanical operated scissor lifts, detects catastrophic failure of the drive mechanism and minimizes unwanted descent or uncontrolled rates of descent of the lifts. 
   SUMMARY OF THE INVENTION 
   The present invention includes a method for preventing uncontrolled descent of a scissor lift comprising:
         a) arresting descent of a scissor lift with an safety hydraulic cylinder when a scissor lift is initially stationary or moving upwardly and a scissor lift fails and begins to descend uncontrollably.       

   Preferably wherein said hydraulic cylinder including a slave safety hydraulic cylinder capable of supporting a scissor lift device upon failure of a scissor device. 
   The present invention includes an anti fall device for use with scissor type mechanically actuated lifting devices, said anti fall device comprising:
         a) a means for arresting descent of a lifting device when a lifting device is normally stationary or moving upwardly and a drive assembly of a lifting device fails and a lifting device begins to descend uncontrollably.       

   Preferably wherein said arresting means including a slave safety hydraulic cylinder capable of supporting a lifting device upon failure of a drive assembly. 
   Preferably wherein said hydraulic cylinder including a one way check valve for preventing reverse hydraulic fluid flow upon uncontrolled descent of a lifting device thereby arresting movement of said hydraulic cylinder and arresting descent of a lifting device. 
   Preferably wherein said drive assembly including a ball screw/ball nut type mechanical drive. 
   Preferably further including a means for controlling descent of a lifting device when a lifting device normally moving downwardly and a lifting device fails and begins to descend uncontrollably. 
   Preferably wherein said control means includes an hydraulic velocity fuse in fluid communication with said hydraulic cylinder, said velocity fuse triggered at a preselected fluid flow rate for controllably lowering a lifting device. 
   Preferably wherein said control means includes an hydraulic velocity fuse fluidly connected in series with a release solenoid defining a circuit A for allowing fluid flow through said velocity fuse when a lifting device moving downwardly and for closing off said circuit A when a lifting device is stationary or moving upwardly. 
   Preferably further including a lowering means for manually lowering a lifting device at a controlled rate of descent. 
   Preferably wherein said lowering means including a normally closed manual lowering valve fluidly connected to a circuit B which is in parallel to circuit A for manually controlling hydraulic fluid flow to said safety hydraulic cylinder thereby manually lowering said lifting device. 
   Preferably wherein said control means housed within a safety manifold which is in fluid communication with said hydraulic cylinder. 
   The present invention includes in combination an anti fall device and a lifting device comprising:
         a) a means for arresting descent of said lifting device when said lifting device is normally stationary or moving upwardly and a drive assembly of said lifting device fails and said lifting device begins to descend uncontrollably.       

   Preferably wherein said arresting means including a slave safety hydraulic cylinder moving in conjunction with said lifting device capable of supporting said lifting device upon failure of said drive assembly. 
   Preferably wherein said hydraulic cylinder including a one way check valve for preventing hydraulic fluid flow upon uncontrolled descent of said lifting device thereby arresting movement of said hydraulic cylinder and arresting descent of said lifting device. 
   Preferably wherein said drive assembly including a ball screw/ball nut type mechanical drive. 
   Preferably wherein said lifting device including a scissor type lift. 
   Preferably further including a means for controlling descent of a lifting device when a lifting device normally moving downwardly and a lifting device fails and begins to descend uncontrollably. 
   Preferably wherein said control means includes an hydraulic velocity fuse in fluid communication with said hydraulic cylinder, said velocity fuse triggered at a preselected fluid flow rate for controllably lowering a lifting device. 
   Preferably wherein said control means includes an hydraulic velocity fuse fluidly connected in series with a release solenoid defining a circuit A for allowing fluid flow through said velocity fuse when a lifting device moving downwardly and for closing off said circuit A when a lifting device is stationary or moving upwardly. 
   Preferably further including a lowering means for manually lowering a lifting device at a controlled rate of descent. 
   Preferably wherein said lowering means including a normally closed manual lowering valve fluidly connected to a circuit B which is in parallel to circuit A for manually controlling hydraulic fluid flow to said safety hydraulic cylinder thereby manually lowering said lifting device. 
   Preferably wherein said control means housed within a safety manifold which is in fluid communication with said hydraulic cylinder. 
   Preferably further including the step of controlling descent of a scissor lift with a velocity fuse when a scissor lift normally moving downwardly and a lifting device fails and begins to descend uncontrollably. 
   Preferably wherein said velocity fuse in fluid communication with said hydraulic cylinder, said velocity fuse triggered at a preselected fluid flow rate for controllably lowering a scissor lift.
         a) arresting descent of a scissor lift with an hydraulic cylinder when a scissor lift is initially stationary or moving upwardly and a scissor lift fails and begins to descend uncontrollably.       

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a flow chart indicating the steps of operations of the anti fall device when the platform is moving upwards. 
       FIG. 2  is a flow chart indicating the steps of operation of the anti fall device when the platform is in the stationary position. 
       FIG. 3  is a flow chart showing the steps of operation of the anti fall device when the platform is moving in the downwards direction. 
       FIG. 4  is a schematic hydraulic circuit diagram showing the safety hydraulic cylinder together with the safety manifold components. 
       FIG. 5  is an upright perspective schematic view of a mechanical scissor lift with the drive assembly and platform and base. 
       FIG. 6  is a schematic perspective view of the drive assembly apart from the lift. 
       FIG. 7  is a plan and side view of the drive assembly showing the anti fall device including the safety hydraulic cylinder and safety manifold. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Definitions 
   Scissor Lift: A raising/lowering device that is supported by one or more pantograph legs sections. 
   Velocity fuse: A hydraulic safety valve that will close (and remain closed) when the velocity of fluid moving through the valve exceeds a predetermined rate. Hydraulic pressure must be applied to the base port to release a locked velocity fuse. 
   Check valve: A device that allows flow of a liquid or gas in one direction only, this includes hydraulic valves that can be controlled manually, pneumatically or hydraulically to selectively block or permit fluid flow as required. For purpose of this application by way of example the term check valve includes but is not limited to present day check valves, pilot operated check valves, poppet valves which are unidirectional and bidirectional, spools, and directional control valves. 
   The present invention an anti fall device shown generally as  20  in the Figures, includes a safety hydraulic cylinder  100  and a safety manifold  200  which is mounted on and used in conjunction with lifting devices and preferably used in conjunction with a scissor lift  50  as shown in the Figures. 
   The present invention anti fall device  20  will be shown deployed in a scissor lift  50 . Those skilled in the art will recognize that the anti fall device  20  can also be used with lifting devices having configurations other than the one depicted in the attached Figures. For the purposes of explaining the present invention anti fall device  20 , we have chosen to depict anti fall device  20  deployed in a simple scissor lift  50  having a mechanical type drive mechanism. 
   Scissor Lift Components Referring now specifically to  FIGS. 5 ,  6  and  7  a scissor lift shown generally as  50  includes the following major components, namely: platform  52 , base  54 , legs  56  having cams  58  mounted thereon and a drive assembly  60  having the anti fall device  20  incorporated therein. The function of scissor lift  50  is simply to raise and lower platform  52  to a preselected and predetermined height in a controllable fashion through microprocessor and/or other mechanical control means. The lift shown as scissor lift  50  in  FIG. 5  is used in various industries for various purposes and particularly is used in the automotive industry for sub assembly and final assembly of automotive components and vehicles. Personnel are often moving in and around scissor lift  50  during its operation and therefore, unpredictable lowering or raising of platform  52  is undesirable in that it can cause bodily injury to persons in the near vicinity of scissor lift  50 . 
   To address this issue, the present invention anti fall device  20  has been adapted to minimize and/or prevent uncontrolled descent or fall of platform  52 . 
   Referring now to  FIGS. 6 and 7  which depict drive assembly  60 , the major components of drive assembly  60  include anti fall device  20  which includes safety hydraulic cylinder  100  and safety manifold  200  deployed onto drive assembly  60  as shown in  FIGS. 6 and 7 . 
   Drive assembly  60  includes a gear motor  302  for a rotatably driving ball screw  304  which in turn interacts with ball nut  306  for linearly urging strong back  318  back and forth along guide rods  320 . Gear motor  302  is connected to ball screw  304  via a transmission and axle pin tube  316  and it interacts with ball nut  306 , such that rotation in one direction of ball screw  304  retracts strong back  318  in direction  312  thereby raising platform  52  through the interaction of cam followers  310  with cams  58  located on legs  56  of scissor lift  50 . 
   On the other hand rotating ball screw  304  in the opposite direction, extends strong back  318  in direction  314  therefore allowing cam followers  310  to move along cams  58  in such a manner that platform  52  is lowered. 
   This mechanical structure is well known in the art and utilized for many applications including mechanical scissor lifts as shown as  50 . Different variations and/or geometries can be used which essentially provide for the same affect, namely the raising and lowering of a platform  52 . 
   Most failures of scissor lift  50  occur in the drive assembly  60 , namely failure of the ball nut  306 /ball screw  304  arrangement or some system failure in the gear motor  302  which includes a motor brake and other mechanical components. 
   Anti fall device  20  is effective in preventing catastrophic or uncontrolled falling of platform  52  when failure of drive assembly  60  occurs. Anti fall device  20  will in many instances be ineffective in preventing fall of platform  52  if there is a catastrophic failure of a major structural component of scissor lift  50  such as collapse of one of the legs  56 . 
   This type of scissor lift failure is however, much less frequent than failure of drive assembly  60  and therefore, it is desirable to have some type of anti fall mechanism which would prevent uncontrolled descent of platform  52 , should there be a drive assembly  60  failure. 
   Anti Fall Device Components 
   Anti fall device  20  includes the following major components namely: safety hydraulic cylinder  100  and safety manifold  200 . Referring now to  FIG. 4  which schematically depicts the hydraulic circuitry of safety hydraulic cylinder  100  as well as safety manifold  200 , anti fall device  20  will now be described with reference to FIG.  4 . 
   Anti fall device shown generally as  20  is comprised of two major components, namely safety hydraulic cylinder  100  which is operably connected to safety manifold  200 . 
   Safety hydraulic cylinder  100  is preferably a hydraulic cylinder having a cylinder rod  102 , cylinder wall  104 , piston  106 , fluid reservoir  108 , reservoir casing  110  and a check valve  202 . Safety hydraulic cylinder  100  is essentially a slave cylinder in that under normal operating conditions it does not impart lifting forces to raise or lower platform  52  of scissor lift  50 . The normal lifting and lowering operations of scissor lift  50  are carried out by drive assembly  60  which consists of mechanical drive including a ball screw  304 /ball nut  306  arrangement. Gear motor  302  imparts the forces necessary to raise and lower platform  52  of scissor lift  50 . 
   Therefore, safety hydraulic cylinder  100  is essentially a passive hydraulic cylinder which becomes active in the case when a catastrophic failure of drive assembly  60  occurs, such as when ball nut  306  fails or when there is failure of the drive system motor brake. 
   Safety manifold  200  which is operably connected to safety hydraulic cylinder  100  is the hydraulic controlling circuits which become active during catastrophic failure of the drive systems. Safety manifold  200  includes two major hydraulic circuits namely, circuit A denoted as  112  and circuit B denoted as  114  in FIG.  4 . 
   Circuit A includes check valve  204 , a velocity fuse  212 , a release solenoid  214  having a check valve  206  therein. 
   Circuit B  114  includes a pressure switch  216 , a manual lowering valve  218 , including a check valve  208  therein as well as a fixed orifice  220 . 
   The operation of safety hydraulic cylinder  100  together with safety manifold  200  is best described by breaking it down into three distinct motions of scissor lift  50 . Namely:
         1. With platform  52  moving upwards.   2. With platform  52  stationary.   3. With platform  52  moving downwards.
 
Platform Moving Upwards
       

   Referring now to  FIG. 1 , the sequence of operations when the platform is moving upward is described in FIG.  1  and here below.
         1. Hydraulic fluid is flowing freely through check valve  202  within safety hydraulic cylinder  100 —shown as  401 .   2. In case of catastrophic failure of the drive system:—shown as  402 .   3. The platform becomes supported by safety hydraulic cylinder  100  since hydraulic fluid flow is blocked by check valve  202 —shown as  403 .   4. Hydraulic fluid also cannot flow through circuits a  112  or b  114  due to a de-energized manual lowering valve  208  and a de-energized release solenoid  214  respectively—shown as  404 .   5. Pressure switch  216  closes indicating that safety hydraulic cylinder  100  is supporting the load—as shown in  405 .
 
Platform Stationary
       

   With the platform stationary:
         1. Platform is supported by the drive system&#39;s motor brake—as shown in  411 .   2. In case of catastrophic failure of the drive system—as shown in  412 .   3. The platform is supported by safety hydraulic cylinder  100  and hydraulic fluid flow is blocked by check valve  202 —as shown in  413 .   4. Hydraulic fluid also cannot flow through circuits a  112  or b  114  due to a de-energized manual lowering valve  208  and a de-energized release solenoid  214  respectively—as shown in  414 .   5. Pressure switch  216  closes indicating that safety hydraulic cylinder  100  is supporting the load—as shown in  415 .
 
Platform Moving Downwards
       

   With the platform moving downwards:
         1. Release solenoid  214  is energized allowing hydraulic fluid flow through velocity fuse  212  of circuit a  112 —as shown in  421 .   2. If descent speed reaches a pre-set limit velocity fuse  212  shuts and locks safety hydraulic cylinder  100  in position—as shown in  422 .   3. Pressure switch  216  closes indicating that safety hydraulic cylinder  100  is supporting the load—as shown in  423 .   4. Energizing manual lowering valve  218  enables hydraulic fluid flow through circuit b  114  and fixed orifice  220  which allows the platform to be lowered at a slow and controlled speed—as shown in  424 .       

   It should be apparent to persons skilled in the arts that various modifications and adaptation of this structure described above are possible without departure from the spirit of the invention the scope of which defined in the appended claim.