PLATEN PRESS Technical Field The present invention relates generally to platen presses and, in particular to a method and apparatus for facilitating the maintenance of platen presses of the type that include multiple platens that are clamped together between a fixed upper bolster and a movable lower bolster.
Background Art Presses having multiple moving platens are commonly used to process sheet material, such as rubber and wood products. In the type of press to which this invention pertains, the platens are clamped between a fixed upper bolster and a movable lower bolster (termed an "up-stroking" press). Main cylinders are pressurized and exert a significant upward force on the movable bolster in order to create a clamping force on the platens. In this type of press, the cylinders are mounted to or are carried by the press frame and the actuating rods of the cylinders are attached to the movable bolster. When the press is opened, the moving bolster moves downwardly and when in this retracted position, there is very little access to the cylinders. These hydraulic components require periodic maintenance including, but not limited to, the replacement of seals and related components. Because these components cannot be serviced or replaced with the movable bolster in the retracted position, the bolster must be maintained at an elevated position when service or maintenance is being performed on the components mounted to the frame. Because it is not desirable to maintain the elevated position of the bolster using press hydraulics, it is typical for the maintenance personnel to move or install, temporarily, special purpose support stands into a position between the frame and the lower bolster. The support stands support the lower bolster at a predetermined height during the maintenance operation. These support stands can be extremely cumbersome to move and, as a consequence, maintenance on a press can be very difficult and time consuming because significant time is spent in installing and removing these temporary support devices. Disclosure of Invention The present invention provides a new and improved platen press and method for facilitating maintenance of certain components forming part of the press. According to one aspect of the invention, the platen press includes a fixed upper bolster, a reciprocally movable lower bolster that is urged towards the fixed upper bolster by at least one fluid pressure operated bolster actuator that acts between a frame and the lower bolster. A fluid pressure operated bolster support system is used to maintain the lower bolster at a raised position in order to facilitate maintenance on the press. The bolster support system supports the lower bolster at the raised position independent of the fluid pressure operator bolster actuator. According to a feature of the invention, the bolster support system includes at least two bolster support assemblies with each assembly including a bolster support post that is movable between retracted and maintenance positions. In the illustrated embodiment, the posts are moved by a pneumatic actuator. According to other features of the invention, sensors are used to monitor the position of the support post and preferably also detect when a support post is engaged by the lower bolster. According to another feature, each support post is held in a cradle and more particularly, each support post defines pin structure that is pivotally engageable with the cradle. According to a further aspect of the invention, the press includes at least one vertical structural member which may be a guide for guiding movement of the lower bolster as it moves towards the upper bolster. The bolster support system includes at least two support stands that are arranged as a pair and located on either side of the structural member. According to this feature of the invention, the support stands are interconnected by a lock out member when the support stands are in the retracted position such that the lock out member engages the support structure if the support stands are urged towards the maintenance position. Within this preferred arrangement, the support stands can only move to the maintenance position when the lock out bar is released in order to decouple the paired bolster support assemblies. In the illustrated embodiment, one end of the lock out bar is pivotally connected to one of the support posts of a pair and the other end of the lock out bars releaseably engages the other of the posts of a pair. A sensor detects when the lock out bar is engaging the other post. In the preferred embodiment, the support posts each mount a post cap at their upper ends which include spring members for equalizing the loading among the supports assemblies when engaging the lower bolster. A control system is disclosed which monitors the sensors and controls the communication of fluid pressure to various pressure operated actuators in response to conditions detected by the sensors. According to another aspect of the invention, a method for performing a maintenance function on a press of the type that includes an upper fixed bolster and a lower moveable bolster, is disclosed. The method includes the provision of at least two bolster support assemblies which each include a bolster support member moveable between maintenance and retracted positions. When maintenance is to be performed, the lower bolster is raised to a predetermined raised position. The bolster support members are then moved from their retracted positions to their maintenance positions where upon the lower bolster is lowered onto the support members. The method also contemplates using a sensor to detect when the support members are in their maintenance positions, before the bolster is lowered. In a more preferred embodiment of this method, bolster support assemblies are located on either side of a structural member forming part of the press. The bolster support assemblies are interlocked when they are in their retracted position so that they are inhibited from moving to their maintenance positions until the support posts are decoupled. In the preferred embodiment, fluid pressure operator actuators are used to move the bolster support members between their retracted and maintenance positions and associated sensors are used to detect when the support posts are in the maintenance position. According to the invention, a bolster support system is integrated into the platen press which can be easily activated by the operator when maintenance of the press is needed. The support system includes a plurality of movable support assemblies that are operated by fluid pressure operated actuators. In the preferred method of operation, the moving bolster is raised to a predetermined height and the support assemblies that are mounted to the press are moved from a retracted position to a bolster support or blocking position. The moving bolster is then lowered onto the support assemblies and is supported at an elevated position during the maintenance of the press. According to the invention, each support assembly includes a support post that is pivotally held in a cradle that is mounted to the frame of the machine. A fluid pressure operated actuator which, in the preferred embodiment is pneumatically operated, is operative to swing each post between retracted and operative positions about an axis defined by an associated pin located at the bottom end of each post. Switches monitor the position of the posts and inhibit operation of the press if anomalies in the post positions are detected. To inhibit inadvertent movement of the post from the retracted position to the bolster blocking position, the posts are arranged in pairs and disposed on either side of guide columns forming part of the press. A locking bar is used to couple the upper ends of the paired posts together. The locking bar inhibits movement of the post from the retracted position to the blocking position because if the posts are moved, the locking bar contacts the column, which inhibits further movement. The position of the locking bar is also monitored by a switch which senses whether the locking bar is fully engaged by the support posts and inhibits press operation should a fault be detected. Additional features of the invention will become apparent and a fuller understanding obtained by reading the following detailed description made in connection with the accompanying drawings. Brief Description of Drawings Figure 1 is a perspective view of a platen type press of the type that the present invention pertains; Figure 2 is a fragmentary side elevational view of a press of the type shown in Figure 1 , illustrating a bolster support system embodying the present invention; Figure 3 is a fragmentary top plan view of the press portion shown in Figure 2; Figure 4 is fragmentary end view of the press portion shown in Figure 2; Figure 5 is an enlarged fragmentary view of the press showing details of a bolster support assembly forming part of the bolster support system of the present invention, shown in a retracted position; Figure 6 is an enlarged, fragmentary view showing a bolster support assembly in an bolster blocking or bolster support position; Figure 7 is a side view of a pair of support posts that form part of a paired support assemblies; Figure 8 is a top view of the support posts shown in Figure 7; Figure 9 is a schematic representation of a pneumatic control circuit for controlling the operation of a pneumatic portion of the bolster support system; and, Figure 10 is a ladder diagram of a control circuit for the bolster support system of the present invention.
Best Mode for Carrying Out the Invention Figure 1 illustrates the overall construction of a multiple platen press which includes a fixed upper bolster 10 and a movable lower bolster 12, between which are positioned a plurality of movable platens 14. The movable bolster 12 is moved upwardly by several main ram cylinders 16, and by a plurality of jack ram cylinders 17 which are positioned in a balanced and symmetrical manner. The construction of the main ram cylinders 16 and the jack ram cylinders 17 may be conventional. In general the jack cylinders 17 are used to close the press i.e. move the bolster 12 from a lowered position to an upper position where the platens are clamp together between the upper and lower bolsters 10, 12. The main cylinders 16 are then pressurized to apply an significant clamping force to the platens during a curing or vulcanizing step. Each of the movable platens 14 is connected to a plurality of control cylinders 18 which are arranged in four groups of cylinders 20, 22, 24, 26, each group being mounted on a separate support assembly 28 which is pivotally connected at one end to the fixed upper bolster 10. The other end of the support assembly 28 is pivotally connected to the upper end of a pivot arm 30 which is pivotally attached at its lower end to a bracket 32 fixed to the movable lower bolster 12. In operation, the movable platens 14 are clamped between the movable lower bolster 12 (which moves upwardly) and the fixed upper bolster 10. The lower bolster 12 is moved upwardly by the jack ram cylinders 17. Each of the movable platens 14 is connected to four or more adjusting cylinders 18, each from a different one of the four or more groups of cylinders 20, 22, 24, 26 adjacent to the four corners of the platen. These four control cylinders maintain the platen level in a precisely adjusted spacing relative to its adjacent platen. The control system and hardware for achieving the control movement of the lower bolster 12 and platens 14 is considered conventional. A detailed description of the mechanism by which the movement in the platens is controlled can be found in U.S. Patent 5,634,398, owned by the present assignee and hereby incorporated by reference. As is also conventional, the press, including the main and jack ram cylinders 16 and 17, is mounted on a fixed frame 34 secured to a concrete pad by legs 36 in a conventional manner. Each of the main ram cylinders 16 includes a piston 38 which is secured to the bottom of the movable lower bolster 12 and is movable upwardly in a parallel relationship with a plurality of vertical guide rods or columns 40. In like manner, each of the jack ram cylinders 17 includes a piston 41 which is secured to the bottom of the movable lower bolster 12 and is operative to move the lower bolster upwardly during a press closing portion of a processing cycle.. The upper bolster 10 is fixed to the frame by attachment to the top of the guide rods 40 and to a press cap 42 in a conventional manner. As is conventional, material to be processed is loaded onto each of the platens 14. The jack ram cylinders 17 are connected to a source of fluid pressure which causes associated pistons to extend, thus raising the lower bolster 12. Concurrent with raising of the lower bolster 12, the control cylinders 18 are also raised due to the interaction of the pivot arm, thus raising the common support assemblies 28 upwardly. This motion raises all of the control cylinders 18 and, thus, raises the movable platens 14. The movement of the platens 14 is coordinated with the movement in the lower bolster so that all platens move to abutting contact concurrently, rather than sequentially as would occur if only the lower bolster 12 was used to move the platens 14 into abutting contact with each other. As is known, a platen press of the type illustrated in Figure 1 is used to process, cure, or vulcanize sheet material. In general, material to be processed is laid on the upper surface of each platen 14. After the material is placed on the platens 14, the press is closed, as described above, clamping the platens 14 together in a tight confronting relationship. The cylinders 16, 17 apply a desired clamping pressure so that the material to be processed, located between the platens, is under constant pressure during the processing cycle. Referring also to Figures 2 and 3, the present invention provides a mechanism for facilitating maintenance of the lower portion of the platen press. It should be noted here that Figures 2-4 are actually split views. A portion of each Figure illustrates the movable bolster 12 in its retracted or lower position, whereas the other portion of the Figure illustrates the bolster 12 in a raised, maintenance position. As seen best in Figure 1 , when the press is open and the lower bolster 12 is in the open position, there is not much room between the movable bolster 12 and the frame 34. In particular, there is generally insufficient room to perform maintenance and repairs on the main ram cylinder 16, the jack ram cylinder 17, the guide rods 40, etc. Over the life of the press, wear parts on these hydraulic components, such as seals, must be replaced. In order to perform maintenance on these press components, the moving bolster 12 must be elevated in order to provide adequate access to the components. In normal operation, the movable bolster 12 is raised by hydraulic pressure. For maintenance operations, it is not feasible to rely on the hydraulic system to maintain the elevated position of the movable bolster 12. According to the preferred embodiment of the invention, the hydraulic system is used to raise the bolster 12 to a height sufficient to provide access to the components mounted in the frame or base of the press and once raised, a bolster support system, constructed in accordance with the preferred embodiment of the invention, is used to maintain the elevated position of the moving bolster. The support system inhibits lowering of the bolster 12 even if hydraulic pressure is terminated to the main ramp cylinders 16 and/or the jack ram cylinders 17. Referring also to Figure 4, the bolster support system includes a plurality of support assemblies indicated generally by the reference character 50 that are mounted to or on the frame 34 of the press. The support assemblies 50 and are movable from a retracted or stowed position to a bolster engaging or blocking position. In the blocking position, the support assemblies 50 abuttably engage the bottom of the movable bolster 12 and support the bolster 12 a predetermined distance above the frame 34. As indicated above, in the preferred and illustrated embodiment, a plurality of movable support assemblies or support stands 50 are provided. In particular, and as best seen in Figure 3, eight support assemblies 50 (shown best in Figure 3) are utilized for a press of the type illustrated in Figure 1. In accordance with the invention, the support assemblies 50 are arranged in pairs with the support assemblies of a pair being positioned on either side of an associated guide rod or column 40 (shown best in Figure 3). Referring in particular, to Figures 5 and 6, each support assembly 50 includes a post 60 that is movable between a retracted or stowed position (shown in Figure 5) and a maintenance position (shown in Figure 6). In the preferred embodiment, the post 60 is moved between its stowed and maintenance positions by an associated fluid pressure operated actuator 70. In the illustrated embodiment the actuators 70 are pneumatically operated. The height at which the moving bolster is supported above the frame 34 is a function of the length of the support posts 60. The left half of Figure 4 illustrates the posts in their bolster supporting position, whereas the right half of Figure 4 illustrates the support posts 60 in their retracted or stowed positions. When the posts 60 are in the retracted position the moving bolster 12 is permitted to descend to its lower or open position. A lower end of each post 60 includes a lateral pin 74 (which may be integrally machined into the post) which is rotatably supported in a cradle 76 that is secured to the frame 34. The pin 74 defines a lateral axis of rotation for the post 60 and is held in the cradle 76 by a cradle cap 78 that is suitably secured as by bolts 80 to the cradle 76. With this preferred construction, the pin 74 exerts only a compressive force on the cradle 76 when the post 60 is loaded during a maintenance operation, i.e., when the movable bolster 12 is lowered onto the post 60. As a consequence, the pin 74 is not subjected to a tension or shear force. The top of each post 60 mounts a post cap 61. A plurality of beveled washers or Belleville springs 82 are mounted between the cap 61 and the top of the post 60 and serve to equalize the loading among the support assemblies 50 and accommodate slight variations in post lengths or bolster misalignments. According to a feature of the invention, the position of each post 60 is monitored. In particular, a switch assembly 90 is mounted in each saddle 76 and is used to determine and/or confirm that the associated post 60 is in the retracted position (the position shown in Figure 5). As will be further explained below, when maintenance is to be performed on the press, the bolster 12 is raised and the support posts 60 are moved to their vertical positions (shown in Figure 6) by their associated actuators 70. According to the invention, a mechanical stop assembly 94 is provided as part of each support assembly 50 against which an associated post 60 abuts when the post is moved to the vertical, maintenance position. This position of the post 60 is monitored by a switch assembly 95 which forms part of the mechanical stop assembly 94 and is actuated when the post 60 abuts the stop assembly 94. As seen best in Figure 5, the post defines a switch actuation region 98 which actuates the switch 95 when the post 60 reaches the vertical position shown in Figure 6. The region 98 may comprise a precisely ground surface on the post 60. According to another feature of the invention, the presence of the moving bolster 12 on the post 60 is also monitored. In particular, a switch 96 is mounted near the top of four (4) of the eight posts 60; preferably, the switches are mounted to the "corner" posts indicated by the reference character 60a. The switches 96 are actuated by the lower bolster 12 as it contacts the top of the corner posts. When all four switches 96 are actuated, it provides a positive indication that the lower bolster 12 is resting squarely on the support posts 60. According to a feature of the invention, a control circuit (shown in Figure 10) which may form part of the overall press control system, monitors the states of the switches 90, 95 and either signals the operator or inhibits operation of the press and/or the movement of the posts 60 if the switches indicate the presence of an anomaly. It has been found that switches sold by Scientific Technologies Inc. under part nos. STI SL M22M and STI 5L-M21M can be used for the switches 90, 95, respectively. In the illustrated embodiment, the extension and retraction of the post actuators 70 is controlled by a pneumatic control system illustrated in Figure 9. The pneumatic control system is connected to a source of compressed air indicated generally by the reference character 100 which is typically available at locations where this type of platen press is used. The control system includes a conventional filter, regulator and lubricator module, indicated generally by the reference character 104. The communication of pressurized air to rod and cylinder ends 70a, 70b of each actuator 70 is controlled by a lever or solenoid operated three position valve 110 (in Figure 9 a lever operated valve is shown). In the center position, illustrated in Figure 9, the actuators 70 are isolated from both the source of compressed air 100 (which is fed to the valve 110 through a supply conduit 112 and from an exhaust line 114. When the control valve 110 is shifted to the right as viewed in Figure 9, compressed air is communicated to a main feed conduit 114 which is connected to branch conduits 114a. Each branch conduit 114a is connected to cylinder ends 70b of an associated pair of actuators 70. As should be apparent, when the control valve 110 is shifted to the right, the cylinder ends 70b of each actuator 70 are pressurized causing extension of the associated actuating rod 70c. As the rod 70c extends, air in the rod end 70a of each actuator 70 is discharged into associated branch conduits 118a and is ultimately exhausted to the exhaust line 114 through a feed conduit 118 that is connected to the control valve 110. When the control valve 110 is shifted towards the left (as viewed in Figure 9), pressurized air is communicated to the branch conduits 118a which, as indicated above, are connected to the rod ends 70a of associated actuators 70. Pressurization of the rod ends causes the rods 70c to retract. As they retract, air in the cylinder ends 70b of each actuator 70 is exhausted to the exhaust line 114. In the preferred and illustrated embodiment, each of the supply lines feeding the rod ends and cylinder ends 70a, 70b of each actuator include an inline flow controller indicated generally by the reference character 116. As is known, the flow controller includes a check valve 116a and a restrictor 116b. The check valve 116a is arranged so that when the associated chamber in the actuator 70 is being supplied air, the air flows into the actuator unrestricted. However, when the air in the associated chamber of the actuator is being exhausted, the check valve 116a closes and the air being discharged must pass through the restrictor 116b forming part of the flow controller 116. By controlling the discharge of air from the actuators 70, movement in the associated posts 60 is controlled. In the illustrated embodiment, when the cylinder ends 70b of the actuators 70 are pressurized, extension of the actuating rods 70c causes the associated post 60 to be driven towards the vertical position (shown in Figure 6), whereas pressurization of the rod ends 70a of the actuators urges the associated posts 60 toward their retracted position (shown in Figure 5. According to a feature of the pneumatic control system, a lockout valve 120 is positioned intermediate the actuator control valve 110 and the source of pressurized air 100. The lockout valve 120 is used to inhibit the communication of pressurized air to the post control system when the platen press is in operation. The lockout valve 120 may take various forms and may include electrically controlled valves or valves that are mechanically locked with a suitable locking device. A valve suitable for this application is available from Parker Hannifin Corp. under the model no. LV4NA8. The lockout valve 120 or, for that matter, other electrically controlled valves may be used to inhibit operation of the bolster support subsystem if the switches indicate that one or more posts 60 are out of position. According to another feature of the invention, inadvertent movement of the support assemblies 50 during press operation is mechanically inhibited. According to this feature of the invention, each pair of support assemblies 50 includes a lockout mechanism to inhibit inadvertent movement in the associated posts 60. Referring to Figures 7 and 8, and as indicated above, the support assemblies 50 are arranged in pairs with the posts 60 of a pair being positioned on either side of a guide or column 40. When the press is in normal operation, a lockout bar 130 is removably secured between the pair of posts 60. When the posts 60 of a pair are interconnected by the lockout bar 130, the posts 60 are inhibited from moving to the vertical position because should movement occur, the associated lockout bar 130 will contact the associated column and further movement of the posts 60 will be inhibited. Referring, in particular to Figure 7, one end 130a of the lockout bar 130 is pivotally attached to one of the posts 60' of a pair. An opposite end 130b of the lockout bar 130 includes a notch 132 which is engageable with an abutment pin 134 forming part of the other post 60" of the pair. In the preferred construction, the position of the lockout bar 130 is monitored by a switch 138. In the preferred and illustrated embodiment, the switch 138 forms part of an integral, solenoid operated latching mechanism. The mechanism is mounted on the lockout bar 130 and when engaged with the switch 138, will not release until the solenoid forming part of the latching mechanism is energized by the control circuit (shown in Figure 10). Further details of the operation of the latching mechanism will be explained as part of the control circuit discussion and in connection with Figure 10. An integral switch/latching mechanism, suitable for this application, is sold by Scientific Technologies, Inc. under component no. TL5012. Should the lockout bar 130 not be fully engaged with the post 60", the operator is signaled and/or further operation of the platen press is inhibited until the condition is corrected. When maintenance of the press is necessary, the lockout bars 130 are released so that the associated posts are free to move past the columns. If the control system detects the presence of lockout bars 130, pressurization of the actuators 70 is inhibited until the condition is corrected. Figure 10 illustrates a ladder diagram of a control circuit for controlling the overall operation of the maintenance support system. As is known, in a ladder diagram power 5 is supplied to the branch circuits via electrical lines labeled "LV and "N" which are connected to a suitable electrical power source (not shown). The platen press is placed in a maintenance mode by closing the switch 200 (labeled SW 1 ). The closing of switch 200 provides power to latch solenoids 204, 206, 208, 210 which form part of associated latching mechanisms 134 and which, in turn, o allow the release of associated locking bars 130 (shown best in Figure 7). The locking bars 130 can now be moved to the retracted positions (shown in phantom in Figure 7) which will, in turn, enable the posts 60 to be moved to the vertical direction when the associated actuators 70 are energized. The switch 200 also includes a contact that is closed to communicate a signal to a PLC (not shown) telling the PLC that the press is 5 now in maintenance mode. A third contact forming part of the switch 200 completes the circuit to an air valve solenoid 220a which includes a momentary push button 222. Pressing the push button 222 energizes the solenoid 222 which forms part of the air control valve 110 (see Figure 9). In particular, energization of the solenoid 222 shifts the control valve 110 to the left (as viewed in Figure 9) and communicates pressurized o air to the cylinder end 70b of each actuator 70, thus causing the posts 60 to move towards the vertical, maintenance position. If all posts 60 move to the fully upright position, contacts within the associated switches 95 (labeled 95a-95h) will be closed. Conversely, contacts (labeled 90a-90h) which form part of the switches 90 will all be opened. Closure of all of the contacts 95a-95h of the switches 94 will cause a relay 5 230 (labeled CR2) to become energized. It should be noted here that when the posts 60 are moved outwardly to their retracted positions, contacts 90a-90h should all be closed. When all of the contacts (which forms part of the position detecting switches 90) are closed, a relay 234 (labeled CR1 ) is energized. o The control circuit includes two branch circuits 236, 238 which energize respective solenoids 240, 242 (labeled CR5, CR6, respectively) if all of the posts 60 are not fully retracted or not fully rotated to the vertical position, respectively. The relay CR5 is energized if any of the switch contacts 90a-90h are closed (indicating that at least one of the posts 60 is still in the retracted position). If all of the posts are in the retracted position, as explained above, the relay CR1 will be energized and its normally closed contact 248 will open, thus de-energizing CR5. CR5 should be de-energized during maintenance mode if all is in order. If all is normal, CR5 will remain de- energized and CR2 will become energized, thus completing a circuit to the maintenance position relay 250 (labeled CR4) via normally closed CR5 contacts 252 and normally open, but now closed CR2 contacts 254.. Branch circuit 238, which includes the relay 242 (labeled CR6) monitors the switches 95a-95h. If any one of the switches 95a-95h are closed, and relay 230 (CR2) is not energized, relay 242 (labeled CR6) is energized. As explained above, relay 230 (CR2) is energized if all of the switches 95 are closed (indicating that all of the posts 60 are in the vertical, maintenance position). Thus, if all the posts 60 are in the vertical position, the upper fault solenoid CR6 will not be energized since the normally closed contact that forms part of the branch circuit will be opened. A branch circuit 260 includes normally open contacts 262, 264 of the relays 240 (CR5) and 242 (CR6) which, as explained above, are closed should a fault occur in either the switches 90 or 95. If a fault is detected in any of the switches 90 which monitor the retracted position, or the switches 95 which monitor the vertical position of the posts 60, one or both of relays 240 (CR5), 242 (CR6) will be energized. If either relay 240, 242 is activated, a fault relay 268 (labeled FLT) is energized, and an alarm strobe 270 is activated to indicate to operators that a malfunction has possibly occurred. If all is in order (no faults are present), the bolster 12 is then permitted to be lowered onto the posts 60. This is accomplished by branch circuit 274 which includes a PLC contact 278, a normally open contact 280 of the maintenance position relay 250 (CR4), a push button 282, a normally closed momentary push button 284, and a normally closed contact 286 of the fault relay 268 (FLT). If a PLC (programmable logic controller, not shown) forming part of the platen press control, determines that no conditions exist that would not allow the bolster 12 to be lowered, the PLC contact is closed. If no faults are detected in the contacts 90a-90h of the switches 90 and all switch contacts 95a-95h of the switches 95 are closed, the relay 50 (CR4) will be energized thus closing the CR4 contact 280. If no faults exist, the fault relay FLT will remain de-energized and, thus, the normally closed contact will remain closed. Under this no fault condition, pressing the push button 282 will energize a solenoid valve 288. Energization of the solenoid operated valve 288 opens the valve and allows pressurized fluid in the main and jack ram cylinders 16, 17 to be released through a restriction (not shown) so that the descent of the lower bolster 12 occurs slowly and in a controlled manner. As the bolster 12 is lowered onto the " corner" posts 60a, the switches 96 mounted to the corner posts 6OA will be closed, thus closing their associated contacts 96a-96d which form part of a branch circuit 290. The closure of all four post contacts 96a- 96d causes a relay 292 (labeled CR7) to be energized which will close normally open contact 292a of the relay 292 (CR7) that forms part of the branch circuit 274. With the contact 292a closed, the solenoid valve 288 will continue to be energized even if the push button 282 is released, thus causing the total depressurization of the main and jack cylinders 16, 17. Finally, a branch circuit 296 controls the illumination of a "clear to perform maintenance light" 298 which indicates that the press is now in a condition which will enable maintenance to be performed. In particular, PLC 300 contact will close if the PLC does not detect any anomalies. If the hydraulic pumps for powering the main and jack cylinders are off, an associated contact 302 will also close. As long as the maintenance position relay 250 (CR4) is energized, its associated contact 250b will also close. As indicated above, if all four post switches 96 are closed indicating that the lower bolster 12 is squarely on the corner posts, the relay 292 (CR7) will remain energized and cause the CR7 contact to close. If no faults are detected, the fault relay 268 (FLT) will remain de-energized and, as a result, the clear to perform maintenance indicator 298 will be illuminated. When maintenance is complete, the lower bolster 12 must be raised using the hydraulic system forming part of the platen press. Once the bolster 12 is raised, a push button 306 forming part of a branch circuit 310 is pressed to energize a solenoid 220b which forms part of the air control valve 110. When the solenoid 220b is energized, the valve is shifted to the right (as viewed in Figure 9) which allows air in the cylinder ends 70b of the actuators 70 to be exhausted while concurrently pressurizing the rod ends 70a of the actuators 70. This will cause the rod 70c of each actuator 70 be retracted, thus moving the posts 60 to the retracted position. Once in the retracted position, the locking bars 130 are moved to their locked positions where they engage the other post 60" of the pair (shown best in Figure 7). The maintenance switch 200 is then moved to the off position which de-energizes the lock solenoids 204, 206, 208, 210, thus inhibiting movement of the locking bars 130 to the retracted position. The present invention thus provides a maintenance support system for the moving bolster 12 which is easily moved into position and does not require the use of separate support stands. When the maintenance operation is completed, the support assemblies 50 are easily moved to their retracted or stowed positions, thus reducing the time that the press is down for maintenance. Although the invention has been described with a certain degree of particularity, it should be understood that those skilled in the art can make various changes to it without departing from the spirit or scope of the invention as hereinafter claimed.
