Abstract:
Method and apparatus for eliminating the danger of inadvertent failure of a weight-bearing retraction system, such as a dryer hood retraction system. A load lifted using a fluid cylinder can be easily locked in place against gravity by using a double rod ended cylinder, where the rod end not exerting the force is permitted to move through a clearance hole while the load is being lifted, and is then blocked to prevent the return motion until the load is to be released.

Description:
BACKGROUND OF THE INVENTION 
     In web printing and drying operations, it is often desirable that the web be contactlessly supported in order to avoid damage to the web itself or to the coating (such as ink) previously applied to one or more surfaces of the web. One conventional arrangement for contactlessly supporting the web includes horizontal upper and lower arrays of air bars between which the web floatingly travels. Hot air issuing from the air bars both dries and supports the web. Such dryers for running webs and the like are typically designed with upper and lower hoods. Each array of airs bars is in air-receiving communication with upper and lower headers. The upper header and upper air bar assembly comprise the upper hood of the dryer, and the lower header and lower air bar assembly comprise the lower hood of the dryer. These upper and lower hoods are retractable with respect to each other, primarily to allow a web to be threaded through the machine, and also to allow for the periodic maintenance and replacement of the air bars and other dryer internals. 
     The upper and lower hood retraction system generally utilizes fluid cylinders to retract the hoods, the fluid cylinders being driven either pneumatically or hydraulically. However, sudden inadvertent pressure loss or the like to the cylinders can cause the retraction system to fail, and the dryer hood to collapse. In order to avoid such a catastrophe, the retracted hood is usually manually blocked in place or automatically pinned in place using auxiliary equipment. However, such a safety measure is generally inefficient and unreliable. 
     SUMMARY OF THE INVENTION 
     The problems of the prior art have been overcome by the present invention, which provides a method and apparatus for eliminating the danger of inadvertent failure of a weight-bearing retraction system, such as a dryer hood retraction system. More specifically, a load lifted using a fluid cylinder can be easily locked in place against gravity by using a double rod ended cylinder, where the rod end not exerting the force is permitted to move through a clearance hole while the load is being lifted, and is then blocked to prevent the return motion until the load is to be released. 
     It is therefore an object of the present invention to provide a simple and efficient method of preventing dryer hood collapse when lifting with a pneumatic or hydraulic cylinder. 
     It is a further object of the present invention to provide apparatus for accomplishing the aforementioned method. 
     These and other objects of the invention will become apparent upon reference to the following detailed description of the invention and accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a tending side view of a web flotation dryer illustrated in the closed position; 
     FIG. 2 is a drive side view of a web flotation dryer illustrated in the open position; 
     FIG. 3 is a side view of the dryer of FIG. 1; 
     FIG. 4 is a side view of the dryer of FIG. 2; 
     FIG. 5 is a side view of a fluid cylinder used to move the slide gate into the locked position; and 
     FIG. 6 is a side view of the adjustable stop plate assembly in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Although for illustration purposes the dryer shown is a web flotation dryer, it should be understood by those skilled in the art that the present invention is applicable to other types of dryers, such as roll support and arched dryers, and equipment other than dryers which utilize load-bearing retraction systems, especially fluid cylinder retraction systems. Similarly, although the dryer illustrated in the drawings includes three dryer zones, the present invention is applicable to dryers having any number of dryer zones. 
     Turning first to FIG. 1, there is shown a split enclosure drying hood including an upper hood 10 and a lower hood 12. In the closed position, a clearance gap 13 is formed between the hoods 10, 12 in which the traveling web W is floatingly supported between upper and lower air bar arrays (not shown) in air-receiving communication with the upper and lower hoods, respectively. The upper and lower hoods 10, 12 can be further separated from one another with a retraction system in order to thread the web through the dryer or maintain or replace dryer internals. Such a system is conventional in the art, and may for example include a guiding devices 15, 16 in addition to the retraction cylinder rod 30, along with associated equipment. The present invention is not limited to any particular retraction system. 
     The retraction system of the present invention comprises an air cylinder 20 (in the embodiment shown, three on each side of the dryer; the actual number used can vary and depends in part on the number of dryer zones and overall dryer length) that includes a double rod ended cylinder rod 30. One end 30&#39; of the cylinder rod 30 is fixed to either the upper or lower hood of the dryer by any suitable means, such as clamp 31 and mounting bracket 32. The opposite end 30&#34; of the double rod ended cylinder rod 30 is moveable through a clearance hole in the base 8 of the unit (FIG. 3), between a first open position (FIG. 4) and a second closed position (FIG. 3). Base 8 can be mounted directly to the dryer, or can be mounted on associated auxiliary dryer support equipment as indicated by the dotted lines in FIG. 3. As the retraction system operates to retract hood 10 from hood 12, the cylinder 20 moves accordingly. 
     In order to block the return movement of the cylinder rod 30 into the aperture in base 8, a mounting bracket stop plate 14 is provided, which is coupled to a flat bar 5 spanning the length of the dryer. A plurality of TEFLON strips 6 are placed along the length of flat bar 5 for ease of sliding the unit in place. The flat bar 5 is in turn coupled to a fluid cylinder 35, such as a hydraulic cylinder, the details of which are illustrated in Figure 5. The stationary end 35&#39; of cylinder 35 is fixed to mounting bracket 36 as shown in FIG. 5. The rod end 35&#34; of cylinder 35 is coupled to mounting plate 37, which in turn is fixed to mounting bracket stop plate 14 on one of the retraction devices. Actuation of the cylinder 35 causes mounting bracket stop plate 14 to move, which in turn causes flat bar 5 to move, thereby resulting in the movement of the other mounting bracket stop plates 12 of the other retraction locking devices. This movement shifts sliding gate 25 into and out of position, either blocking or opening the aperture in the base 8, as the case may be. Reference to FIG. 1 shows each mounting plate 14 in the far left position, which situates the sliding gate 25 out of cylinder rod 30 blocking position and allows the cylinder rod 30 to pass through the aperture in the base 8 (not shown). Reference to FIG. 2 shows each mounting plate 12 in a central blocking position, which situates the sliding gate 25 over the aperture in the base 8 and prevents the cylinder rod 30 from passing through that aperture, thereby locking it in place. Since the cylinder rod 30 is locked in place, failure of the retraction system will not result in the collapse of the load. 
     In order to compensate for manufacturing and field assembly tolerances, the height of the sliding gate 25 can be adjusted with a pair of adjusting bars 21 (only one shown) which are clamped to the sliding gate 25 and coupled to the slide gate mounting plate 14, as shown in FIG. 6. 
     The operation of the retraction locking system of the present invention can be described as follows. When the dryer is in the unretracted mode (i.e, the hood is closed) as shown in FIGS. 1 and 3, each cylinder rod 30 is positioned through an aperture in the base 8 of each retraction locking device. When the dryer is moved into a retracted position (i.e., the hood is open) as shown in FIGS. 2 and 4, the fluid cylinder 35 is activated, which causes a shift of sliding gate mounting plate 14 associated with one of the air cylinders 20, which in turn moves flat bar 5 and causes the other sliding gate mounting plates 14 associated with the remaining air cylinders 20 on that side of the dryer to shift, thereby causing the sliding gate 25 to slide under the cylinder rod 30 and block its return motion into the aperture in the base 8, thereby preventing the dryer hood from lowering. A limit switch 40 can be employed to prove that the slide plate 25 is in position or out of position.