Fluid cylinder with motion buffered ram assembly
BACKGROUND OF THE INVENTION 
     The present invention relates generally to an improved double acting fluid cylinder of tandem chamber construction, wherein a primary chamber is utilized to provide initial motion in the ram in a first direction and wherein a tandemly arranged secondary chamber is provided with a resiliently biased secondary piston to buffer and control the rate and extent of the initial motion induced in the ram and to provide secondary reverse motion in an amount proportionally less than the initial motion so as to control the amplitude or ultimate extent of motion induced in the ram in each operational event. 
     Fluid actuated cylinders are utilized for a wide variety of purposes. The operating parameters of cylinders are determined, to a great extent, by the type of operating fluid utilized, the operating pressure and capacity of the source, as well as the manner in which the fluid is controlled while being delivered to the chambers. The cylinder arrangement of the present invention, being tandem, is designed for use preferably with a pulsed pneumatic source in the primary chamber, to achieve quick initial response, and with a hydraulic fluid being provided in the secondary chamber, for buffering and modifying the ultimate response of the cylinder to the pulsed input, thus providing an air-hydraulic combination cylinder with desirable operational characteristics. 
     As indicated, fluid actuated cylinders are utilized for a variety of purposes. The design of the present air-hydraulic combination cylinder makes it particularly adapted for use with devices requiring a rapid initial drive or stroke response to an indicating signal, with the initial drive phase or stroke being followed by a subsequent relaxation phase wherein a portion of the ram motion induced in the initial phase is reversed. 
     The cylinders of the present invention are particularly adapted for use in controlling and steering high speed webs such as endless abrasive belts or the like which move or travel at high rates of speed in an orbital path along two or more drums which define the orbit. In a typical two drum orbital arrangement for an abrasive belt, one drum drives the belt, with the second or idler drum preferably being used as a &#34;tracking&#34; roll or drum for the system. Because of the high rates of speed normally involved in such orbital webs or belts, highly responsive steering corrections are required in order to control, steer and properly track the web along its orbital path and limit the extent to which the belt will wander or otherwise experience axial run-off. 
     Most abrasive belt tracking systems employ at least two sensors in order to properly steer the web, one being disposed at each lateral edge of the normal tracking path of the belt. Since the sensors employed normally respond to the occurrence of an abnormal tracking condition, it is normally necessary to oversteer the tracking device to be able to correct the run-out and at the same time properly steer or guide the web along a desired axial path. Because of the high speeds involved, the correctional response or motion must be undertaken rapidly in order to prevent axial run-off of the belt. In order to prevent ultimate over-correction or constant hunting of the system, it has been found desirable to control or steer the web with a correctional cycle which includes two separate phases, the initial phase consisting of an over-adjustment or drive pulse of excessive magnitude, followed by a relaxation phase which consists of a partial reversal of the initial drive pulse. The over-adjustment occurring in the initial phase is designed to reverse the direction of &#34;wander&#34; of the belt. The relaxation or buffer phase permits partial reversal of the initial over-adjustment with the reversal occurring at a somewhat slower rate than that taking place in the initial phase. In other words, in the initial phase of the correctional cycle, a first over-adjustment pulse is delivered to the cylinder to cause the ram to move in a first direction, and during the relaxation phase, a partial and relatively slow reversal of motion of the ram occurs. In the air-hydraulic combination cylinder of the present invention, the initial over-adjustment stroke or pulse is obtained by the action of the primary pneumatic chamber, with the primary piston providing the rapid initial response in the ram along a first operational direction. Thereafter, in the relaxation phase a reversal of motion occurs to accommodate and mollify the initial over-adjustment. In a typical belt control application, therefore, the initial over-adjustment is sufficient to immediately correct and reverse the axial travel condition of the belt to prevent run-off, with the relaxation or reversal phase being undertaken to accomplish some residual correction of the axis of travel. In this fashion, control of the web and/or belt is achieved by establishing a new operating datum point for the tracking system each time a belt travel correction event or cycle occurs. 
     The improved air-hydraulic combination cylinder of the present invention is uniquely adapted for belt tracking control, among other applications where response of the above type is desired indicated or required. Typically, the improved air-hydraulic cylinders of the present invention include a single housing and ram with tandemly arranged primary and secondary chambers. A double-acting ram is slidably mounted within both chambers of the housing, and primary and secondary piston members are operatively coupled to the ram within the respective chambers. The primary chamber has a pair of primary fluid ports in communication therewith delivering primary fluid thereto, in this case pneumatic fluid. While steady-state delivery of pneumatic fluid may be utilized in some applications, the device of the present invention is particularly adapted for use with pulses of fluid delivered thereto. Since, the primary fluid ports are typically disposed on opposite sides of the primary piston, double-acting motion of the primary piston and ram may be achieved. The secondary chamber is provided with a pair of secondary fluid ports, with these ports being arranged on opposite sides of the secondary piston. A fluid conduit directly interconnects the secondary ports, one to another, to hydraulically couple the opposed ends of the secondary chamber together and to permit hydraulic fluid to move therethrough at a controlled rate in response to motion of the secondary piston. The secondary piston is resiliently coupled to the ram through two groups of normally counter-balanced springs, so that the ram may move axially relative to the secondary piston. The motion of the secondary piston relative to the ram is dependent upon forces generated in the opposed counter-balanced springs, with movement of the secondary piston forcing hydraulic fluid through the interconnecting conduit to mutually opposed sides of the piston. Accordingly, the motion of the ram is buffered in both its rate and amplitude, with the buffering action occurring as a result of forces generated in the resilient counter-balanced spring members of the secondary piston and through transfer of hydraulic fluid due to movement of the secondary piston within the secondary chamber. 
     SUMMARY OF THE INVENTION 
     Therefore, it is a primary object of the present invention to provide an improved fluid cylinder means of tandem design, wherein both primary and secondary chambers are utilized to control motion of a double-acting ram, and wherein a primary chamber is utilized to receive pulses of compressed fluid to provide the primary motion to the ram, and wherein a secondary chamber is provided to buffer the motion both with respect to rate and ultimate extent of motion. 
     It is yet a further object of the present invention to provide an improved air-hydraulic combination cylinder employing tandemly arranged primary and secondary chambers, and wherein the primary chamber produces a rapid stroke or response in the form of an over-travel of the ram along a first direction of motion, and wherein the secondary chamber provides a buffering action which produces relaxation and modest reversal of motion of the ram along a second or opposite direction, and with the relaxation motion induced by the secondary chamber being at a lower rate and at a proportionally smaller magnitude than that of the initial over-travel motion, thereby achieving a new operational datum point for the ram which is slightly offset from the original starting point of the ram at the initiation of the operational cycle. 
     Other and further objects of the present invention will become apparent to those skilled in the art upon a study of the following specification, appended claims and accompanying drawings. 
    
    
     IN THE DRAWINGS 
     FIG. 1 is a sectional view taken through the diameter of a fluid cylinder assembly prepared in accordance with the preferred modification of the present invention; and 
     FIG. 2 is a schematic diagram illustrating the fluid cylinder assembly of the present invention arranged in combination with a typical circuit for controlling the action of the cylinder. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In accordance with the preferred embodiment of the present invention, and with particular attention being directed to FIG. 1 of the drawings, the fluid cylinder means generally designated 10 includes a housing 11, cylindrical in form, having axially aligned primary and secondary chambers 12 and 13 disposed therewithin. Also, end caps are provided as at 14 and 15, with end cap 14 having a mechanically coupling member 16 secured thereto, and with end cap 15 having a bore therewithin as at 17, provided with appropriate seals as at 18. Ram 19 is disposed within the tandemly aligned primary and secondary chambers 12 and 13, with ram 19 being, of course, arranged for double-acting motion within the chambers. With attention being directed to primary chamber 12, it will be observed that this chamber is provided with a primary piston as at 21, with piston 21 being appropriately sealed to the inner walls of chamber 12 with circumferential seals such as at 22 and 23. Seals 22 and 23 may typically be lip seals or &#34;O&#34; rings. Ports 25 and 26 communicate with chamber 12, and provide a means for introducing and exhausting fluid under pressure to chamber 12 to drive piston 21. Typically, ports 25 and 26 will be provided with fittings to couple fluid pressure lines thereto. In the operation of the fluid cylinder 10, pneumatic fluid under pressure will normally be coupled to ports 25 and 26 and controllably introduced thereto and exhausted therefrom. Ram 19 is appropriately coupled to piston 21 by means of the threaded nut shown at 27. In order to preserve the operational and integrity of the system, a typical &#34;O&#34; ring seal will be provided as at 28 to separate the double-acting chambers 29 and 30, one from the other. 
     An intermediate chamber-separating annular ring is provided at 32. Ring 32, as indicated, is provided with a central bore, and with a seal being disposed therewithin as at 33, the seal being held in by place by snap ring 34. Port 26 is, as indicated, disposed within ring 32 to supply air or other gaseous fluid to the primary chamber 12. Also, a second port is provided in ring 32 as at 35 for secondary chamber 13, the operation of which will be described more fully hereinafter. Secondary chamber 13 is, as indicated, disposed between end cap 15 and chamber separating annular ring 32. Ram 19 extends through the entire extent of secondary chamber 13, and as is apparent, secondary piston 36 is disposed therewithin. Secondary piston 36 separates secondary chamber 13 into a pair of opposed chamber portions such at 37 and 38, with chamber portions 37 and 38 being isolated, one from another by means of sealing rings 39 and 40. As is apparent, chambers 37 and 38 are arranged on generally oppositely disposed ends of the secondary chamber 13; separated by the secondary piston 36. 
     Secondary piston 36 is resiliently coupled to ram 19 through two groups of opposed normally balanced and biased spring members such as at 41 and 42. These spring members permit the secondary piston 36 to move axially relative to ram 19 and responsive to forces generated on piston 21 within the primary chamber 12. Resilient springs 41 and 42 are held in place by flanged sleeves as at 43 and 44, along with snap rings as at 45 and 46. The seals are provided inwardly of the springs 41 and 42, as at 47 and 48. 
     For appropriate alignment of piston 36 on ram 19, it is preferable that one or more springs, such as at 41 and 42 be provided. For achieving the objectives of the invention, such springs are normally equally arcuately spaced around the circumference of ram 19. 
     Port 35, as previously indicated, along with an annular clearance zone between the outer surface of rod or ram 19 and the inner surface of end cap 19 provided communication in the fluid circuit portion of the invention. In addition, port 50 is utilized as an auxiliary port primarily for air-bleeding from the system. Therefore, port 35 together with the annular space between rod or ram 19 and the inner bore of end cap 15 provide primary communication with chamber portion 37 and 38, respectively. Port 50 provides additional communication when in normal operation. The port 35 and the annular spacing between rod or ram 19 and end cap 15, together with port 50 are interconnected by means of fluid conduit 51 in order to control the rate of transfer of fluid between chambers 37 and 38. A control means is provided as at 52 to meter the flow of fluid through conduit 51. The amplitude of motion of the ram 19 is controlled in part by the forces available from springs 41 amd 42, with the extent of the motion achieved during the relaxation phases of the operational cycle being controlled by the metering valve 52. Also, for maintaining a constant supply of fluid within the system, automatic fluid filler such as at 53 is provided. These fluid filler systems, which are commercially available, automatically maintain and/or replenish hydraulic fluid which may be lost from the system during normal operation. A check valve is normally provided as at 54 for controlling operation of the automatic filler mechanism. Also, for bleeding air from the system, a bleeder assembly may be provided as at 55. 
     While any typical assembly techniques may be utilized, the arrangement of the present invention may include a system wherein the end caps 14 and 15, along with the intermediate ring 32, may be welded to the cylinder portions 11 and 11a, with cap screws such as at 56 and 57 being provided to complete the assembly. Also, assembly by cap screws will permit inspection and repair of the cylinder when necessary. 
     Attention is now directed to FIG. 2 wherein a typical system for an operational environment is illustrated. This operational environment is selected from a portion of the operational grinding machine disclosed and claimed in U.S. Pat. No. 3,504,458, Richard D. Rutt, assigned to the assignee of the present invention with the exception of the tracking cylinders, it being appreciated that the tracking cylinders of the present invention are substituted for those illustrated in U.S. Pat. No. 3,504,458. Referring now to the diagrammatic showing of FIG. 2, it will be observed that fluid cylinder means 10 is coupled to an operative hydraulic circuit including a source of pneumatic fluid under pressure as at 60, which is connected to a source, such as air or the like, and provided with a typical filter as at 61. For most applications, it is normally sufficient for lines 25 and 26 to be controlled through solenoids which admit air under pressure, when required, and are otherwise normally vented to atmosphere. In other words, the inertia and normal resistance encountered in the fluid portion of the device is adequate to hold the cylinder in a desired position excepting for those occasions when a change or adjustment is indicated. 
     With respect to the system illustrated in FIG. 2, therefore, pressure line 60 is further connected to control valve 62 having a spool valve portion, the position of which is controlled by a switch on a control panel, not shown, for either directing or exhausting air from ongoing pressure line 63. Pressure line 63 is connected to release valve 64 which, in turn, is connected to air discharge jet 65 for discharging air to atmosphere through conduit 66. Also connected to lines 63 is a release valve 67 which, in turn, is connected by means of conduit 68 to a directional valve 69 having a spool valve, the position of which is controlled by a solenoid 70 and a spring member 71. 
     Leading from directional valve 69 is a conduit 72 connected to port 25 of cylinder 10, conduit 72 being provided with a restricted passageway 73 therein to slow the flow of compressed air in one direction, but may be bypassed in the return direction by a conduit utilizing check valve 74. Also leading from directional valve 69 is the second conduit 75 connected to port 26 of fluid cylinder 10, conduit 75 being provided with a restricted passageway 76 therein to slow the flow of compressed air in one direction, but which may be bypassed in the return direction by a conduit having a check valve 77 therewithin. As is indicated, conduits 73 and 76 are disposed in operative parallel relationship with supply conduits 72 and 75, respectively. 
     In the operational embodiment, a sensor of the type typically used for belt tracking purposes, such as an air jet of the type disclosed in Rutt U.S. Pat. No. 3,504,458 may be utilized. Alternatively, electronic systems utilizing photo-responsive sensors may be employed. In either event, these sensors are utilized to activate or control solenoids 70 to displace spool valve within directional valve 69 to connect conduit 68 to conduit 75 to supply a pulse of compressed air to port 26 while exhausting port 25. Ram 19 is moved inwardly to the left in response, so as to move the track roll of a belt tracking system in an appropriate direction to properly control the tracking motion of the belt. When the control system calls for a correction in the opposite direction from that earlier described, a second tracking sensor of the type illustrated in Rutt U.S. Pat. No. 3,504,458 or a photo electric sensor will de-energize solenoid 70, allowing spring 71 to displace spool valve within directional valve 69 and apply a pulse of compressed air to the port 25 and exhaust through port 26, to cause axial motion in the belt, and drive the belt laterally in the opposite direction to achieve the proper correction. 
     Turning now to the details of the cylinder illustrated in FIG. 1, when a pulse of air under pressure is provided to chamber 29 through port 25, ram 19 is moved outwardly in response to the introduction of air under pressure. Thus, ram 19 will be caused to move to the right in view of FIG. 1, and secondary piston 36 moves to the right as well but to a lesser amplitude. The motion of secondary piston 36 is not co-extensive with the motion of rod 19, since springs 42 are compressed, while springs 41 are permitted to expand or relax. When the effects of the pulse of compressed air being applied to port 25 are terminated, the springs 42 which were further compressed, together with springs 41 which were permitted to expand, will relax and return to equilibrium through reverse movement of rod 19 and piston 21. This motion is in a reverse direction, or to the left in FIG. 1, to a point which approaches, but which is not as far to the left as it was in its original position at the beginning of the cycle. Oil, which preferably fills chamber 37 and 38, is caused to move through interconnecting conduit 51, and thus functions to diminish the quantity held in one of the chamber portions, while increasing the quantity held in the other. This displacement of fluid occurs while the primary piston is under the influence of the pulse of air entering the primary chamber, thus displacing hydraulic fluid to the opposite side of the piston 36. The displacement of hydraulic fluid is at a controlled and preferably slow rate with the displacement being dependent upon the setting of metering valve 52. Thus, secondary piston 36, the hydraulic piston, will move or shift or a new location in response to the forces induced upon it, and the displacement of a quantity of hydraulic fluid. Following the termination of the application of the pulse of compressed fluid through port 25, secondary piston 36 will cause ram 19 to move in a reverse direction during the relaxation phase of the correctional cycle. 
     Valve 52, the metering valve, will control and limit the speed as well as the distance that piston 36 can travel during the initial phase of each correctional cycle, and thus the magnitude of the differential motion resulting from each correctional cycle or belt-track controlling event. 
     As has been indicated, when controlling and steering rapidly moving orbital webs or abrasive belts, it is necessary to initially over adjust or steer the tracking device so as to be able to correct the belt track rapidly enough to prevent run-off of the belt. Accordingly, each time a steering or tracking correction is called for, secondary piston 36 modifies the initial over-adjustment through a relaxation phase of the correctional cycle, whereby the position controlling ram undergoes a modest change of axial position at the end of each correctional cycle. After a number of tracking corrections have been made in and along the same direction, the combined action of the primary piston along with the modifying and relaxation action of secondary piston 36 will cause ram 19 to be disposed in a new and proper position, and the rapidly moving web will be tracked and held generally along a desired travel path or axis. Also, drifting of ram 19 will be limited and controlled by the action of the secondary piston within its hydraulic loop. 
     In one typical operational embodiment, the cylinder is provided with an initial correctional pulse which is adequate to move the ram outwardly at a distance of approximately 0.100 inch, with this amplitude representing the over-correction portion of the operational cycle. Thereafter, the cylinder is permitted to recover through motion in the opposite direction generated by the secondary cylinder by a distance of approximately 90% of the amplitude of the over-correctional portion of the cycle. The amplitude of motion which is achieved by the over-correcting pulse is determined by certain of the operating parameters, including the pressure available at the source, along with the time duration of the applied pulse. The magnitude and/or extent of reverse motion is determined by the setting of the metering valve in the hydraulic portion of the system. 
     In order to preserve operational integrity, it is desirable that the axially length of the secondary chamber be greater than that of the primary chamber 11a. Such geometric designs assist in preventing cocking or misalignment of the piston 36 in its chamber, and also aid in extending the life of the seals to preserve operating integrity and metering control. 
     It will be appreciated, of course, that the fluid cylinder design of the present invention has a number of applications, is adaptable for a variety of uses, and is, of course, highly suited for the belt tracking application as described herein.