Abstract:
A personal lift device is disclosed having a motor having an output shaft. A gearing system is operatively connected to the output shaft for increasing torque. A strap for suspending a weight is wound onto a spool and rotating the spool extends and retracts the strap. A drive connection is made between the gearing system and the spool to permit said motor to drive said spool. A brake is associated with said spool to prevent unwanted extension of said strap from said spool, when a weight is suspended by said strap. In a preferred embodiment a clutch is provided between the brake and the drive train, and the greater the weight supported by the spool the greater the braking force. An emergency lift and lower device is also provided in the event of a failure of the motor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division from Ser. No. 11/803,361 filed May 14, 2007, claiming priority to the parent application Ser. No. 10/502,815 filed Jan. 27, 2003, now U.S. Pat. No. 7,240,621. That application was a national stage entry from PCT/CA03/00094 filed Jan. 27, 2007 claiming priority to Canadian Patent Application No. 2,369,668 filed Jan. 28, 2002. The disclosures of the U.S. patent applications are incorporated herein by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     FIELD OF THE INVENTION 
     This invention relates generally to the field of mobility devices, and more particularly to personal lift devices of the type that may be used to raise or lower a physically disabled person for the purpose of moving them. Most particularly, this invention relates to a form of personal lift device that can be activated to raise or lower a patient or physically disabled person. 
     BACKGROUND OF THE INVENTION 
     Personal lift or patient lift devices have been known and used in the past for the purpose of assisting with the mobility of otherwise immobilized patients. An attendant may help physically disabled patients who may have suffered a traumatic injury, stroke or one form of illness or another, and who are unable to move about. However, often such patients may be too heavy to lift or the attendant may not have enough strength to help the patient move. This can be especially true for disabled patients who have reduced mobility but otherwise normal bodily functions. Getting up, going to the bathroom and having a bath, for example, can be difficult for such patients. 
     Personal lift devices that have been used in the past typically include a strap or chain hanging down from a motor assembly, which in turn may be suspended from a movable stand or from a rail carriage riding along an overhead track. An overhead track can be organized to extend from over a bed and into, for example, an adjoining bathroom area, to permit the patient to be raised, suspended, and then moved along the track to a position where they can be lowered into the bathtub for the purposes of a bath, or onto a toilet. 
     Typically such patient lift devices are provided with an electronic lift motor and with an inefficient gear train system. The latter is believed desired, because, in the event of a power failure, the inefficiency of the gear train means there is no quick release or lowering of a patient in a downward direction. In other words, the motor and power train are self-braking. While providing such gearing inefficiencies does act as a safety brake, it also increases the cost, size, and weight of the lift apparatus, since a larger electric motor is required to both lift and lower against the gear train. As well, in the event of a malfunction due to electrical failure of the motor, the patient can be stuck suspended in mid air without any practical way of being released and lowered. Therefore, what is desired is a lighter, simpler, and more efficient device, which can be readily utilized for patient lifting and which preferably includes a safety release to prevent patients from being stranded in a suspended position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference will now be made, by way of example only, to preferred embodiments of the present invention as depicted in the following drawings: 
         FIG. 1  is a perspective view of the present invention, showing the general arrangement of the elements but with an outer housing partially removed for ease of illustration; 
         FIG. 2   a  is a close-up view of the main elements of the present invention; 
         FIG. 2   b  is the same view as  2   a , but with some of the supporting elements removed for illustrating the elements in the drive train; 
         FIG. 3  shows the drive train of the present invention including a emergency lowering mechanism in a storage position; 
         FIG. 4  is the same view as  FIG. 3 , showing the emergency lowering mechanism in a deployed position; 
         FIG. 5  is a view showing forces on a portion of the present invention when supporting a load; 
         FIG. 6  is an exploded view showing the clutch and brake features of the present invention; 
         FIG. 7  is a side view of a coupler connected to the emergency lowering mechanism; and 
         FIG. 8  is a perspective view of the drive train elements of a further embodiment of the present invention. 
     
    
    
     BRIEF SUMMARY OF THE INVENTION 
     According to the present invention a more efficient drive train can be used to reduce the work required to lift and lower patients. A more efficient drive train will result in either a smaller motor being required, or more lifting power being available for a motor of the same size. Quite simply the present invention comprehends having more of the energy of the electrical motor go into the lifting and lowering rather than simply being used to overcome the friction inherent in an inefficient gear train. 
     Another aspect is that the present invention comprehends using a brake associated with the power train to ensure that the patient is not unexpectedly lowered in the event of a power outage or motor failure. In one preferred form of the invention the brake force is related to the amount of weight suspended from the lifting device, in such a way that the greater the weight the greater the braking force. 
     Another aspect of the present invention is to provide a one-way clutch in the drive train to permit the drive train to turn freely as the motor is being used to raise the patient, which in turn lowers the work done by the motor in overcoming the friction during lifting. Most preferably the one way clutch mechanism is installed in at least a portion of the drive train to, for example, isolate the brake from the lifting cycle to reduce the work of lifting. 
     According to a further aspect of the invention, a manual emergency lowering device is provided which is both effective in terms of overcoming the brake, and which is readily accessible when needed and conveniently stored out of the way when not. In particular the present invention provides an emergency lower device that may be easily used by an attendant standing on the ground, even though the lift device may be located at or near the ceiling and otherwise out of reach. 
     The invention also comprehends a device in which non-emergency lowering, as well as lifting, are accomplished in the ordinary course through the manual effort of an attendant standing on the ground. In this device neither a motor nor a separate manual emergency lowering element would be required. 
     Therefore there is provided according to one aspect of the present invention a personal lift device comprising: 
     a motor having an output shaft; 
     a gearing system operatively connected to said output shaft for increasing torque; 
     a strap for suspending a weight; 
     a spool for suspending said strap and for extending and retracting said strap; 
     a drive connection between said gearing system and said spool to permit said motor to drive said spool; and 
     a brake, associated with said spool to prevent unwanted extension of said strap from from said spool, when a force is applied to said strap. 
     There is further provided, according to a second aspect of the present invention, a braking system for a personal lift device of the type where a weight is suspended by a strap and the strap may be extended or retracted from a spool, the braking system comprising: 
     an operative connection between said brake and said spool; 
     a clutch to permit said spool to turn without overcoming the brake when said weight is being raised by said strap; 
     a frictional slip interface which slips when said weight is being lowered; 
     wherein a braking force generated at said frictional slip interface is correlated to said weight, to generate a larger braking force under greater weights. 
     According to yet a further aspect of the present invention there is provided an emergency lift and lower assembly for a personal lift device comprising: 
     a cover releasably attached to said device, 
     an elongate manually actuable element stored in said cover, and 
     a drive train take off point associated with said cover, wherein, upon said cover being detached from said device, said element engages said take off point to permit movement of said element to raise or lower a weight suspended by said device. 
     According to yet a further aspect of the present invention there is provided an emergency lift and lower assembly for a personal lift device comprising: 
     a cover for protecting a drive train of said personal lift device; 
     a take off means extending from said cover and accessible from outside of said cover, said take off means operably connected to a drive train of said personal lift device; and 
     a manually actuable element, releasably connected to said take off means, to remotely drive said take off means when said element is connected and to permit said element to be stored out of the way when said element is disconnected. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows the main elements of the present invention. In  FIG. 1  there is shown a housing  10  for a personal lift device  11 . The housing  10  is attached to a base plate  12 . The housing  10  covers the motor and drive train (described below) of the present invention and protects the same from dirt, dust, contaminants and the like. For ease of illustration, the housing  10  is shown partially removed, but it will be understood that in the preferred form the housing  10  fully surrounds and encloses the base plate  12 , as well as the inner workings of the personal lift device  11 . 
     Shown extending from the housing  10  is a lifting and lowering strap  14  with a looped end  16 . The lifting and lowering strap  14  may be attached to a patient sling or other lift device  17 , and by means of operation described below, the strap  14  is raised and lowered for the purpose of lifting the patient for facilitating movement of the patient carried in the lift device  17 . Also shown are upper attachment elements  18 ,  19 , that are used to attach the unit to a stand or overhead track  20  by means of a carriage (not shown) or the like. Although shown as a track  20 , the present invention may also be used with a moveable stand or tripod, such as will be known in the art. 
       FIG. 2   a  shows the main elements of the present invention suspended from the plate  12 . The main elements include an electric motor  21 , which is mounted under the plate  12  to a drive train support box  24  by screw fasteners or the like. The motor may be a 12 VDC Valeo right angle gear drive motor, or any other drive motor that can supply the desired the desired torque and speed. The motor  21  includes an output or drive shaft  22 , which extends towards the drive train support box  24 . The drive train support box  24  is also attached to the support plate  12  and includes various elements of the drive train. A pair of parallel worm gears of which one is shown at  26  are driven by the drive shaft  22  through appropriate gears as explained below. The worm gears are rotatably supported by support fittings  30 ,  32 , at one end as shown. Most preferably each of the worm gears are supported on a single worm shaft having at least one ball bearing. Also shown is a spool support plate  34  with spool axle  35  in the support box  24 . 
       FIG. 2   b  shows the same elements as  2   a , but with the support plate  12  and support box  24  removed, to reveal the second worm gear  28 . As shown, the drive shaft  22  includes a drive gear  38  which simultaneously drives both worm gears  26 ,  28 , through mating gears  40 ,  42 , at the motor end of the worm gears  26 ,  28 . Both of the worm gears in turn drive the spool  44  by interacting with teeth of opposed helical side spool gears shown at  46  and  47 . Most preferably the worm gear/spool gear ratio is about 4:50, but other ratios may also be used and are comprehended by the present invention. As can now be appreciated the motor, when energized, will turn the drive shaft, which in turn will drive the worm gears  26 ,  28 . Then, the worm gears turn and cause the spool  44  to turn. The strap  14  suspended from the spool  44  is either taken up or lowered depending upon the direction the motor  21  is turning. 
     It can now be appreciated that an additional benefit of the twin worm gears  26 ,  28  of the present invention is that the forces on the two worm gears are only about one half of the forces otherwise generated on a single worm gear, which means that lower strength materials can be used in the construction of the worm gears. In some cases the twin worm gear design will permit hardened plastics to be used, which reduce the weight and expense of the present invention. Otherwise machined metal parts can also be used. The present invention comprehends that the output gear of the motor interacts with the drive gears of the worm gears at a ratio of 2:1. 
       FIG. 2   b  also shows the elements of the emergency lower device according to the present invention. In particular, there is shown a take off gear  60 , attached to a manual lower shaft  62 , which extends through a bearing holder assembly  64  and ends in chain gear  66 . The take off gear  60  engages the gears  40 ,  42 , and is either driven or drives the same, depending upon the circumstances, as described in more detail below. The bearing holder assembly  64  rotatably houses the manual lower shaft  62  while holding the shaft in place. The assembly  64  preferably includes pivoting chain guides  68 ,  70  which are sized and shaped to guide, for example, a chain  74  over chain gear  66 . 
     A chain  74  ( FIG. 4 ) is carried in the cover  72  and is most preferably in the form of a loop or endless section. The chain includes link elements sized and shaped to engage the teeth of chain gear  66 . The cover  72  is releasably mounted on the bearing holder assembly  64 . Releasing the cover  72  simply requires a sharp pull in a downward direction. Most preferably the cover  72  is sized, shaped and attached in a way that enables it to be easily dislodged with any convenient reach extender, such as a broom handle, or the like. As the cover  72  is lowered, the chain  74 , otherwise stored in the cover  72 , plays out and extends down. Most preferably the chain is of a length suitable for being easily reached by a person standing on the floor, even if the device  11  is mounted on the ceiling. Good results have been achieved with the chain  74  falling four feet below its raised position. Further the cover  72  most preferably includes a chain post so that the cover is permanently attached around the chain  74 . 
     In the raised position the chain  74  is preferably supported above the chain gear  66 , and so is not driven while the motor is raising or lowering patients. The balance of the chain  74  is neatly stored inside of the cover  72 . The present invention comprehends all forms of manually actuable elongate elements for use in the emergency lift and lower situation, such as ropes, extended crank handles, and the like, but a chain  74  is the most preferred form. The chain can be held out of engagement with the gear when not in use, and is flexible enough to be easily stored in the cover  72  when not in use. Then, when needed the chain  74  can be dropped onto the gear  66  as the cover  72  is lowered. As the cover  72  is further lowered, the flexible chain  74  will deploy out of the cover  72  and extend below the device  11  until it is in easy reach. The positive engagement of the links of the chain  74  on the chain gear  66  sprockets is helpful in providing enough traction to the chain  74  on the gear  66  to permit enough force to be generated to raise or lower the weight on the strap  14  without weight on the strap  14  without slipping. 
     Thus, the present invention comprehends forming the cover so that when the cover is pulled down, the chain is then caused to sit on and engage with the chain gear  66 . As can be now understood, with the chain hanging down and in easy reach, an attendant is provided with a means to easily lower the patient down, even if the motor has malfunctioned. As the attendant pulls on one side of the chain, the chain gear will be caused to rotate, in turn rotating the worm gears and the spool, and thus raising or lowering the strap  14  as needed. Also shown is a gear box  300 , which may be used to alter the gear ratio of the shaft  62 , to permit the mechanical advantage to be optimized. For example, increasing the mechanical advantage through the gear box  300  will make it easier to use the chain for lifting, but require more movement of the chain to cause movement of the patient. Reducing the mechanical advantage through the gear box  300  means that the chain requires more force to move, but causes greater relative movement of the strap and the patient. The present invention comprehends adjusting the mechanical advantage, first, by sizing the gears  60 ,  40 , and  42  and  38 , and then, if desired, through use of a gear box  300  as shown. 
     Turning to  FIG. 3 , the cover  72  is shown mounted on the chain gear. The chain guides  68 ,  70  are in a raised position, supporting the chain  74  free of chain gear  66 . It will be understood that various configurations of elements can be used, and that the preferred form of chain guides that act to guide the chain in a lower position but pivot to a raised chain supporting position provides good results. 
     In  FIG. 4  the cover is shown pulled off and exposing the chain gear  66 , with the chain  74  engaging the chain gear  66 . It can now be appreciated that pulling on the chain  74  in the direction of arrow  80  causes the chain gear to rotate in direction of arrow  82 , causing the strap  14  to move in direction of arrow  84 . Conversely, pulling the chain  74  in direction of arrow  86  causes a rotation in direction of arrow  88 , moving the strap  14  in the direction of arrow  90 . In this way an easily accessible and manually operable emergency lift or lower facility is provided to the device of the present invention. 
     It can now be understood that the chain gear  66  is in essence a take off means, for providing access to the drive train of the lift and lower device from outside. While a chain is one form of releasable element for remotely driving the take off means, other forms, such as releasable crank handles, are also comprehended. Such a crank handle can be stored unattached, and then lifted and attached if and when needed. 
     Another configuration that has provided adequate results is shown in  FIG. 7 . In this arrangement a coupler  50  may be inserted between the shaft  62  and the gear box  300 . The coupler functions to disengage or separate the chain gear  66  from the shaft  62  during normal operation of the lift device, i.e. when the patient load is being lifted or lowered by rotation of the motor  21 . When the emergency lower device is needed, the coupler  50  can be activated to connect shaft  62  to gear chain  66 . 
     As shown in  FIG. 7 , shaft  62  is provided with an open-ended slot  52  at a termination point. A corresponding shaft  53  having a slot  56  projects from gear box  300 . Shaft  53  ends at coupler  50 , which is a generally hollow tubular element intersected by pins  54  and  55 . Coupler  50  is attachable to shaft  53  through the insertion of pin  54  into slot  56 , and is slidable over shaft  53 . The hollow interior of coupler  50  is also sized and shaped to fit over shaft  62 , and pin  55  is sized and shaped to fit inside slot  52 . 
     Pin  54  has an external portion  57  that engages a lock  58 . As shown, lock  58  may be simply a hook or stop against which external portion  57  can rest. An elastically deformable element or spring  59  fits over shaft  53  between the coupler  50  and the side of gear box  300 , and provides a bias urging coupler  50  towards shaft  62 . In  FIG. 7  coupler  50  is shown in a retracted or locked position, with external portion  57  resting against lock  58 . It can be appreciated that in this position chain gear  66  will be unaffected by the spinning of lower shaft  62 . 
     When it is desired to employ the emergency lower device, simple rotation of chain gear  66  will cause coupler  50  and external portion  57  to rotate, freeing portion  57  from lock  58 . The latent energy of spring  59  will be released, impelling coupler  50  towards shaft  62 . The shafts  62  and  53  will interconnect through insertion of pin  55  into slot  52  of shaft  62 . It shaft  62 . It can be appreciated that slot  56  should be sized sufficiently deep to ensure that coupler  50  does not slip off shaft  53  when pin  55  is inserted into slot  52 . Alternatively, slot  56  can be made closed on both ends to ensure that slipping is prevented. 
       FIG. 8  shows an alternate embodiment of the present invention in which the device is operated manually rather than by electrical power. Motor  21  is accordingly replaced by a chain gear  92  and corresponding chain  94 . In particular, chain gear  92  may be configured to rotate the same output shaft, which turns drive gear  38 , as that otherwise rotated by motor  21 . Since motor or electrical failure is not a concern in this embodiment, a separate emergency lower facility is not needed. This embodiment may also perform adequately with a single worm gear, as shown in  FIG. 8 , in cases where the expected load is suitably reduced. 
     It can be appreciated that pulling of the chain  94  by an attendant will raise or lower the patient in a manner similar to that described previously with respect to the emergency lower device. The chain gear  92  and chain  94  could also be enclosed by a cover similar to the cover  72  used with chain gear  66 . It can be further appreciated that this embodiment could also be realized by removing the motor  21 , gear box  300 , and coupler  50 , and relying exclusively on the emergency lift and lower device in the ordinary course. 
     In  FIG. 5  certain elements of the present invention are shown in isolation for ease of understanding. In particular, the spool  44  is shown, with the lifting strap  14  extending below the spool  44 . One of the worm gears  26 ,  28  is shown with the mating gear  40  at one end and a braking assembly  100  at the other end. The strap is wound around the spool and by means of a strap guide is fed out below the centre of the spool  44 . The weight carried by the spool  44 , indicated by arrow  102 , creates a force  104  that drives the worm gear onto the braking assembly  100 . In the preferred form of the invention, the greater the weight the greater the force on the braking assembly  100 . 
     Turning now to  FIG. 6 , the elements of the braking assembly  100  are shown in exploded detail. In a preferred form a one-way clutch bearing  106  is provided upon which is is mounted a cone shaped brake element  108 . A conical braking or slip surface  110  is formed in the end of the worm gear  26 , which is sized and shaped to match with the conical surface  112  of the cone shaped brake element  108 . A ball-bearing  114  is also mounted onto the same axle as the cone shaped brake element  108 . 
     The operation of the braking assembly  100  can now be understood. By means of the ball-bearing element the cone shaped brake element can be rotated in direction of arrow  116  together with the worm gear. Thus, when raising the strap, the worm gear and brake element rotate together, by means of the ball-bearing. However, in the lowering direction, the ball-bearing is not rotatable, meaning that for there to be any rotation the rotation must occur between the cone shaped brake surface  112  and the slip surface  110  of the worm gear  26 . The cone shaped brake surface  112  will have a braking force that is a function of the seating force, namely how strongly the worm gear is pushed onto the brake surface  112 . As described above the seating force is a function of the weight suspended by the strap, so the greater the suspended weight the greater the seating force and the greater the braking force. Thus, through this interacting structure a braking force can be generated which is larger for larger weights. Thus in the design range of lifting weights for the device, the braking force is self-compensating to be strong enough to support all patients, and yet for lighter patients will be less than for heavier patients. 
     The operation of the present invention can now be understood. When a load is to be lifted, the load is attached to the strap and lifting commences. Because the drive train of the present invention is quite efficient, most of the effort in lifting actually is directed to raising the weight, rather than to overcoming the frictional losses arising from the drive train. As noted, because the brake is mounted on a ball-bearing mechanism, none of the lifting effort is directed to overcoming the braking force, unlike prior art devices. 
     On the other hand, when lowering is required the motor reverses direction and the motor has to generate enough power to overcome the difference between the braking force generated by the brake and the weight. Since the weight is already in the lowering direction, only the difference between the weight and the braking force must be overcome to initiate motion. In this way, while a significant factor of safety can be built into the braking force, braking force, such that for example the braking force generated will always be between 1.5 and 2 times the weight, the motor will only have to generate enough power to overcome the difference between the two. In a similar manner, less effort will be needed to operate a manually powered device of the type shown in  FIG. 8 . 
     A further feature of the present invention can now be understood. The present invention offers a more efficient use of motor power. Even though the braking force increases with increased weight, since the weight being supported is also increased the difference remains within a reasonable range over different weights. Thus the present invention comprehends that the motor be sized and shaped as needed and of a relatively low power to cause the brake force to be overcome and for lowering to be achieved. As this low power will be somewhat constant over a range of weights being lowered, less energy is required for each lowered weight. This contrasts with the prior art, in which the inefficient gear train means that the more weight being supported, the stronger the motor must be (both in terms of maximum torque and total work). Personal lift devices are rated according to how many lift and lower cycles can be obtained from a single battery charge. By increasing the efficiency, as comprehended by this invention, either more cycles can be obtained for the same power leading to a higher rating, or smaller batteries can be used to deliver the same rating at a reduced cost. 
     It will now be understood that the amount of braking force is a function of a number of variables that are interrelated in a complex way. Some of these variables include the size of the in-contact overlapping brake surfaces, the angles at which the surfaces intersect, the smoothness of the surfaces, and the force exerted between the surfaces causing them to come together. By predetermined design these variables can be selected to provide a brake assembly having a preferred brake force profile to facilitate the objectives of the present invention. 
     Most preferably, the present invention will include a form of hand held control to start and control the motor. The control could be either hard wired, by means of a connecting cable to a control circuit in the device, pneumatic, or operable by remote control. In some cases the former is preferred to prevent the control unit from being separated and separated and lost. The present invention comprehends the control unit having, among other things, a raise button or control. Associated with the control system is a limit switch on the motor assembly to prevent the device from being over raised, which could cause damage to the motor and other components. Thus, once the strap has been retracted a maximum amount, the motor will be simply disengaged from further motion in the raise direction by means of the limit switch. 
     Good results have been achieved by forming the worm gear, drive gear, and conical braking surface out of a single machined component. However, the present invention also comprehends having these elements separately mounted in the same functional relationship on an axle. The one-piece construction is preferred for safety and strength reasons. Good results have also been achieved by forming the spool from a single machined component which includes a built in strap anchor and side spool gears, all mounted on a single spool shaft. However, the present invention also comprehends forming the spool gears separately, and simply integrating them with the spool on a single spool shaft. 
     Additionally, for safety reasons it is preferred to include an over-speed governor into the spool. This is shown at  200  in the drawings. The preferred form of governor is simply a latch that is pivotally mounted at one end onto the spool. The mounting is such that when the spool rotates, the other end of the latch is urged outwardly. The faster the spool rotates the greater the outward urging under centrifugal acceleration. The ability of the latch to move will be restricted until a force is generated that represents uncontrolled descent of the strap. Then the latch will extend outwardly, as shown at  202 , and lock the spool against any further rotation. 
     It will be appreciated by those skilled in the art that various modifications and alterations to the invention are possible without departing from the broad spirit of the invention as described above and in the appended claims. Some of these were discussed above and others will be apparent. For example, while use of a chain is preferred, other forms of emergency lower elements can also be used, such as crank handles.