Abstract:
A compact lifter is disclosed which lifts a lifting platen by at least one actuating cylinder with a minimum number of posts or guide shafts to guide the platen as it is being lifted to ensure reliability and reproducibility, each of the posts being received by at least a pair of bearings on each post to hold the post steady and true in position during the lifting operation. The lifter can be in constructed in a two post or a four post configuration, among others. An enclosure is disclosed for completely enclosing the working mechanism to prevent environmental contaminants from entering the workings and damaging the machinery.

Description:
TECHNICAL FIELD 
     This invention relates to a compact lifter, and more particularly to a compact lifter with two guide posts or shafts and first and second linear slide bearings on each of the posts so as to provide improved bearing configurations to substantially prevent deviation from the desired lifting path. 
     BACKGROUND OF THE INVENTION 
     Conventional lifter assemblies have included a top mounting plate by two pair of shafts located thereunder in order to extend and retract the mounting plate so as to lift a workpiece into a desired location. These lifter assemblies are used extensively in manufacturing operations, and find special utility in automotive manufacturing operations for lifting automotive workpiece components to facilitate the placement of the workpiece during the manufacturing operation. 
     In the prior art lifter assemblies, the top mounting plate has a linear actuator cylinder centrally located for lifting the mounting plate, and the pairs of shafts have generally supported base and intermediate plates, where the base plate is slidably attached to a first pair of shafts by a first pair of housings having bearings to slidingly support the shafts, while the intermediate plate is slidably attached to the second pair of shafts by a second set of housings and their respective bearings. This has created three distinct problems for modern manufacturing plants. 
     First, the prior art lifter assemblies required sufficient physical space for both the upward stroke and the bottom stroke of the lifter plate and rods for the lifter assembly. Although attempts have been made to solve this space problem, see for example U.S. Pat. No. 5,690,315, in which two pair of substantially parallel shafts are provided wherein one pair of shafts has the top mounting plate connected to the top of the shafts, while the bottom of the shafts are connected to a separate cross support member, which is, in turn, connected to yet another set of shafts, bearings and all the other necessary parts. This meant that the &#39;315 compact lifter assembly did not require the shafts connected to the top mounting plate to extend beyond the bottom of the lifter assembly, thereby solving the problem of the required sufficient physical space for both the upward and bottom strokes. However, the &#39;315 patent does not address the second and third problems that were presented by the prior art devices. 
     The second problem presented is that these lifter assemblies are used in very dirty environments, and any shavings, weld flash, or the like which are the by-products of the manufacturing operation, can become embedded directly in the bearings, scratching the cylindrical surface of the shaft, or the particles can become embedded in the lubricant used around the shafts and then be dragged into the bearings, causing great harm to the overall system. Traditionally, the lifter assemblies have taken up such a large “footprint” in the plants, that an enclosure to alleviate this problem has been impractical. The reason that the enclosure was not possible is that a constant ratio is needed for direct and constant contact between the actuating cylinder and the moving mounting plate in order to keep the closed dimension of the lifter kept at a constant, in addition to the necessity for keeping the stroke plus bearing ratio constantly engaged. Once these ratios are kept constant, the total workings of the lifter may be enclosed within a tolerably sized sheet metal guard to prevent outside contaminants from entering the enclosed space, thereby preventing harm to the inner workings. As one can imagine, it would be a real advantage to provide an enclosure over the entire unit, both in the retracted as well as the extended positions, such that the working mechanisms are protected from the working environment atmospheric impurities. 
     Moreover, a third problem arose in the prior art assemblies in that the conventional two post lifters actually included four posts, rather than two, to allow for the size of the lifter in an attempt to provide a sure and direct path for the shafts to permit reliable lifting and positioning of the workpiece. It would be a great advantage to the art to be able to actually only have two posts in a “two post” lifter as additional costs to the customer would be alleviated. The prior art four post “two post” lifters needed all four posts in order to have the two additional guide posts or shafts to allow for the size of the lifter in a closed state to be contained in the least amount of space. Furthermore, the additional posts or shafts were necessary to prevent deflection in position and path because the first set of shafts did not support the cylinder in the extended position. The additional number of shafts merely added to the problem of environment dirt contamination because there were twice as many shafts that could have problems. 
     Therefore, it would be a great advantage to the compact lifter if a new compact lifter could be discovered that would alleviate the space problem, prevent contaminants from entering the machinery, and merely utilize two posts, rather than four or six, for a “two post” lifter. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to address these three problems while providing additional reliability of the lifting operation itself, and substantially eliminating any deviation from the position from time to time. This is achieved by a double set of bearings on each of two guide shafts, or posts, in the event of a two post compact lifter, and four guide shafts or posts in the event of a four post compact lifter. Furthermore, this linear configuration allows for exterior plates to be placed around the working mechanisms such that they can be shielded from outside contaminants, including, e.g. Weld flash, dirt, dust, and other by-products of the manufacturing operation. A compact lifter made in accordance with the present invention can include a two post lifter, a four post lifter, or any number of appropriate posts for a lifter, all using these same principles. These compact lifters will produce reliable, predictable and accurate results while minimizing the cost to manufacturer, house and maintain, as well as providing the manufacturing industry with a true two post compact lifter that will extend the life of the actuating cylinder rod bearing and its seal, being protected from atmospheric impurities. 
     Furthermore, compact lifters of the present invention maintain a compact size relative to the stroke of the unit, and the linear relationship of the “stacking” of the bearings provide much greater repeatability than the prior art. 
     Moreover, due to the exterior plates promoted in the present invention, a pneumatic lock-out pin and electrically shut-off mechanism and arrangement is now possible in a new way. During maintenance of the compact lifter, a safe means is necessary to protect the maintenance workers. Prior art inventions did not have the configuration which made possible a pneumatic lock-out device, although the present invention does. The actual lock-out device and pin are the subject of my concurrently filed patent application entitled “ELECTRICAL AND PNEUMATIC LOCK-OUT DEVICE”. 
     Other objects, advantages and applications of the present invention will become apparent to those skilled in the art. For instance, individual lifting devices may require more or fewer posts for lifting, and the advantages of the present is invention can be realized by merely including more or fewer guide posts or shafts and bearing configurations. This extension of my invention can be made by a person of ordinary skill in the art without having to perform undue experimentation. Additional embodiments of the present invention will become apparent when the following description of the best mode contemplated for practicing my invention is read in conjunction with the appendant drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The description makes reference to the appendant drawings, wherein like reference numerals refer to like elements in other figures: 
     FIG. 1 is a perspective view of the two post compact lifter embodiment of the present invention in a substantially retracted position; 
     FIG. 2 is a side elevational sectional view of the two post lifter assembly in a retracted position, showing phantom lines of the compact tear in an extended position; 
     FIG. 3 is a top plan view of the two post compact lifter of FIG. 1 a view taken along lines  3 — 3 ; 
     FIG. 4 is a perspective view of a four post compact lifter made in accordance with the present invention; 
     FIG. 5 is a side elevational sectional view of the four post lifter of FIG. 4; and 
     FIG. 6 is a top plan view of the four post lifter of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In accordance with the present invention, there is disclosed several embodiments of the compact lifter including two and four post lifters, although other numbers of posts, or guide shafts, could be foreseen by one of ordinary skill in the art without undue experimentation. The present invention is described in terms of the two embodiments utilizing two and four post lifters. 
     Referring now to FIG. 1, there is shown a two post compact lifter as generally denoted by numeral  10  including a lifting frame bottom plate  12  shown exploded from the shock stop blocks  14  for clarity, although they are attached in real life, as can be seen in FIG.  2 . Shock stop blocks  14  will be described in more detail hereafter in the context of the shock absorbers. Guide shafts  16  are permanently attached to the bottom plate  12  via the shock stop blocks, although they are not necessary, as the attachment could be direct. Guide shafts  16  are received within a first pair of linear bearings  20 , although any type of suitable bearing can be used prior to being received again through a second pair of linear bearings  30 . Bearings  20  are located with bearing housing  22  that is secured to a back frame member (not shown here) by bearing bracket  24 . A set of shock absorbers  26  is also attached to the bearing housing  22  and the bearing bracket  24  to soften the impact of the retraction of the lifter. The shock stop blocks  14  not only act as the surface onto which one set of the shock absorbers  26  lands, but the shock stop blocks  14  also act as a means for the optional proximity sensor switches  38  which tell the lifter to slow down and stop before the lifter smashes to its fully retracted position (in the event that there were no fail-safe). 
     Still referring to FIG. 1, there is also shown an actuating cylinder  18 , common to most compact lifters, having a cylinder rod  40  extending therefrom for pushing up the platen  34 . Platen  34  is the portion of lifter  10  that contacts a workpiece (not shown in the drawing) and lifts it into position for the work to be done. Actuating cylinder  18  is attached to the underside of bearing plate  28  that has a second pair of linear bearings  30  extending therethrough for receiving guide shafts  16 . Again, linear bearings  30  may also be any other type of suitable bearing, but is shown in the preferred embodiment here. Guide shafts  16  extend through linear bearings  30 , but are permanently attached to the underside of platen  34  in order to steady the platen and ensure its repeatable path. 
     The “stacked” effect of the linear bearing pairs are the reason that this compact lifter is so steady, without deviating from its path during the lifting operation. The first and second pairs of linear bearings being placed on the same guide shaft acts as a brace against movement. The distance between the two is sufficient to provide an assurance of straight movement in the extended position. Guide shafts  16  are preferably from about 1.0 inch to about 3.0 inches in diameter for most applications, although 2.0 inch diameter guide shafts are most preferably used for automotive assembly line applications. 
     In operation of this embodiment, actuating cylinder  18  is hydraulically operated by flexible hydraulic lines attached to the back of the cylinder (not shown in the drawing). Actuating cylinder  18  is filled with hydraulic fluid through the hydraulic lines and cylinder rod  40  is extended, pushing the platen  34  upward. Platen  34  is guided in its upward path by guide shafts  16 , and the guide shafts are guided, in turn, by the first and second pair of linear bearings  20  and  30 , respectively. As platen  34  is the top of a fully integrated lifter frame (the sides of which are not shown in this drawing) and bearing brackets  24  secure the bearings to the frame, the guide shaft  16  travels through the linear bearings  20 , and pulls the frame and the bearing brackets upward along with it. When fully extended, and the guide shafts have traveled as far as they can go, the optional proximity sensor switch registers the location of the platen and the box frame. Then, when the compact lifter is fully retracted, the shock absorbers  26  are used in conjunction with the shock absorbers  26  to softly touch down the lifter to its retracted position, without any damage to the lifter itself or its cargo. 
     Even offset loads are evenly lifted by the compact lifter of the present invention, due to the “stacked” linear bearing configuration. If a part of the lifter cargo is hanging off one of the edges, the present compact lifter will still be able to reliably and positively lift the cargo into position on the assembly line. 
     Referring next to FIG. 2, we see a side elevational view of the compact lifter as shown in FIG.  1 . Like reference numerals indicate like elements of the invention. However, in this figure, the lifter frame is shown as element  36 , surrounding the entire lifter mechanism. First pair of linear bearings  20  are secured to the lifter frame  36  by bearing brackets  24  which are bolted to the frame. Second pair of linear bearings  30  are drilled through the bearing plate and secured therein by bearing sleeves  32 . Although the compact lifter is shown in the retracted position, the extended position is shown in phantom for the sake of understanding. 
     Looking still to FIG. 2, there is a stroke bar  42  attached to the side of the lifter frame  36  so that maintenance crews have a way to lock the lift in the up or in the down position. Stroke bar  42  and lifting frame  36  both contain mating and complementary holes therein which are meant to receive a lock-out safety pin  44 . Once in place inserted through both holes in the stroke bar  42  and the lifting frame  336 , safety pin  44  prevents the lifter from crashing down onto a maintenance crewperson working on the lifter. Even though the electricity might be cut off, the hydraulics or pneumatics may still slip and hurt some one. Therefore, this lock-out safety pin is most helpful during maintenance of this unit. 
     Lifter frame  36  is difficult to show illustrated, as it completely encloses the lifter itself. Otherwise, what is actually seen from the outside of the unit, once assembled, is merely a box that moves up and down. This enclosure is the mechanism that prevents the inner workings from becoming contaminated by dirt, weld flash, or other manufacturing by-product debris. 
     FIG. 3 is the top plan view taken along line  3 — 3  of FIG. 1, showing the relative placement of the guide shafts  16 , actuating cylinder  18 , the cylinder rod  40 , and the shock absorbers  26 . 
     With combined reference, we now turn to FIGS. 4-6, where there is shown the other embodiment of the present invention, that being a four poster compact lifter generally denoted by numeral  50 . Again, like reference numerals refer to like elements in all the FIGS. 4-6. Lifter  50  includes a lifting frame bottom plate  52  attached to shock stop blocks  54 , and is permanently attached to guide shafts  56  at both ends. An actuating cylinder  58  is utilized much the same way the actuating cylinder  18  is used in FIG.  1 . The first pair of linear bearings  60  direct the guide shafts  56  in conjunction with the second pair of linear bearings  70  to reliably and reproducible operate the lifter. First and second pairs of linear bearings are housed by bearing housings  62  and  72 , respectively. Shock absorbers  66  are secured to the bearing brackets  64  which are attached to the lifter frame  76 , again for softening the “touchdown” of the lifter. Optional proximity sensor switches  78  (not shown in FIG. 4) work in conjunction with the shock absorbers to carefully touch down the lifter without damage to itself or its cargo. Cylinder rod  80  extends to lift the platen upwardly with its cargo into the desired position. 
     Further, as shown, the stroke bar  82  can be locked in place with respect to lifter frame  76  with a lock-out safety pin  84  as shown in FIG.  5 . As discussed earlier with respect to FIG. 2, the safety pin acts to prevent any unwanted pneumatic or hydraulic action of the lifter when maintenance crews are working in the frame. 
     As for the operation of the four post lifter illustrated in FIGS. 4-6, the reader is referred to discussions hereinabove as again, this unit works very similarly to the two post lifter shown and described in great detail with respect to FIGS. 1 and 2. Most of the discussion for FIGS. 1 and 2 directly applies to FIGS. 4-6, and consequently will not be repeated in the interests of brevity. 
     Therefore, a compact lifter meeting and exceeding the advantages desired as described above is disclosed herein. The two post lifter is actually a two post unit which provides an extremely reliable and reproducible path for the platen and its cargo to travel, one without deviation from the desired travel path. The four post lifter exhibits similar advantages as the two post lifter. The shop floor “footprint” of the present invention is smaller than the prior art devices, and not only does not sacrifice reliability but rather surpasses the prior art devices in sturdiness and lack of deviation from the intended path. Furthermore, the entire internal mechanics are protected from environmental contaminants such as dirt, debris and weld flash, thereby reducing or eliminating down time for maintenance. Once maintenance is required, the present invention is of such a configuration that the maintenance crew can safely and easily perform the maintenance procedures without the fear of unwanted movement of the lifter, as it will be locked into a single position, without the ability to move. 
     While the present invention has been described with reference to two specific embodiments, it must be realized by those of ordinary skill in the art that these embodiments shall not limit the scope of the present invention. Rather, the invention is only limited by the appending claims.