Patent Publication Number: US-8979154-B2

Title: Clamping attachment with regenerative hydraulic circuit

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/814,080, filed Apr. 19, 2013. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a load handling clamp for use with a forklift or other load handling vehicle and, more particularly, to a load handling clamp having a regenerative hydraulic circuit. 
     Clamp attachments are used on forklift trucks and other load handling vehicles to engage a variety of loads. For example, rolls of paper are commonly engaged and moved with hydraulically actuated paper roll clamps attached to forklift trucks. The forklift truck is maneuvered to locate the paper roll between a pair of clamp arms and when the roll is in the proper position one or more hydraulic actuators are activated to clamp the roll between contact pads at the foremost ends of the arms. Paper rolls commonly weigh in excess of 1000 kilograms (kg.) and the clamp must generate and maintain sufficient clamping force to provide the necessary friction between the contact pads and the paper roll to immobilize the load in the clamp. On the other hand, the clamping force must be controlled to avoid distorting the clamped load or damaging the surface of the load in contact with the clamp. Some lighter loads are particularly fragile and the clamping force must be limited to a fraction of the force that can normally be exerted by the clamp. Clamping force can be reduced by controls that reduce the hydraulic pressure in the actuator(s) but if the pressure is too low the clamp may operate slowly or not at all. The clamping force can also be reduced by reducing the dimensions of portions of the hydraulic actuator but it is expensive to design, manufacture and stock special hydraulic actuators and reducing the size of portions of an actuator may weaken it structurally making the actuator prone to damage during use. 
     What is desired, therefore, is a hydraulically actuated clamp with a substantially reduced clamping force but which includes few custom components, is structurally rugged and which operates quickly and reliably. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective drawing of a forklift truck equipped with a clamping attachment. 
         FIG. 2  is a perspective drawing of an exemplary paper roll clamping attachment. 
         FIG. 3  is a schematic of a regenerative hydraulic circuit for a clamping attachment. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring in detail to the drawings where similar parts are identified by like reference numerals, and, more particularly to  FIGS. 1 and 2 , clamping attachments are used on a variety of load handling vehicles, such as the exemplary forklift truck  20 , to engage and clamp a load for handling, The exemplary clamping attachment  22  includes a frame  24  adapted for mounting on a forklift carriage which is, in turn, movable vertically in the forklift&#39;s tiltable mast assembly  26 . The exemplary clamping attachment  22  is a paper roll clamp which is commonly used in handling cylindrical loads, such as rolls of paper or fiber. The frame  24  of the clamping attachment may include a rotator mechanism enabling the longitudinal axis of a cylindrical load  28  to be rotated from a vertical orientation as illustrated which is convenient for storing or transporting cylindrical loads, to a horizontal orientation  28 ′ which is commonly preferred when winding or unwinding material from a roll for use in a printing press or other machine. 
     The clamping attachment  22  comprises generally, the frame  24 , a movable first arm  30  and a second arm  32 . The second arm  32  may be movable but is commonly fixed to or integral with the frame  24 . The movable arm(s)  30  of the exemplary clamping attachment is pivotally attached to the frame  24  by a hinge comprising a pin  34  engageable with cooperating bores in portions of the arm and frame. The movable arm  30  is typically pivoted relative to the frame  24  by one or more actuators  36 . The clamp arm actuator(s) is typically hydraulically activated and, while it may comprise a hydraulic motor with a rotating motor shaft and suitably connected to the frame and the movable arm; typically, the clamp arm of a clamping attachment is moved relative to the frame by a hydraulic linear actuator or cylinder. The hydraulic linear actuator(s)  36  typically comprise an actuator body  38  pivotally attached to either the frame or the clamp arm by a pin  40  and an actuator rod  42  pivotally attached to the other of the frame or clamp arm by a second pin  44 . By extending or retracting the actuator rods  42  relative to the actuator bodies  38 , the movable arm  30  of the exemplary clamping attachment  22  is pivoted to secure or release a load which is clamped between the contact pads  46  at the ends of the arms  30 ,  32  distal of the frame. 
     Paper rolls can be heavy, commonly weighing in excess of 1000 kilograms (kg.), and often shift during transportation or storage. As a consequence, a paper roll clamp is ruggedly built and has a powerful hydraulic system to provide and maintain sufficient clamping force to prevent the paper roll from slipping from the contact pads and to enable portions of the clamp arms to be inserted between closely packed or shifted rolls. On the other hand, full clamping force may be excessive for lighter loads and excessive clamping force can deform a clamped roll or damage its surface. Clamping force is typically controlled by limiting the fluid pressure applied to the hydraulic actuators which move the clamp&#39;s arm(s). However, reducing the hydraulic pressure to achieve a very low clamping force to protect a clamped load may result in too little pressure to move the clamp arm through its full range of motion or may substantially slow movement of the arm. A low clamping force can also be attained by reducing the area of the piston of a linear hydraulic actuator but a special small actuator assembly can be expensive to manufacture and might be subject to structural damage in the abusive environment that commonly characterizes paper roll handling. Moreover, if the hydraulic pressure or the ratio of the areas of the piston and rod are too low, there may be insufficient force to open the clamp fully. The inventor concluded that the clamping force of a clamping attachment could be limited to a fraction of the clamping force normally available without compromising structural integrity or operation of the attachment and at a lower cost by utilizing a hydraulic circuit incorporating regeneration to actuate the clamp arm. 
     Referring also to  FIG. 3 , the hydraulic circuit  50  of the exemplary clamping attachment  22  is connected to the hydraulic system  52  of a lift truck or other load handling vehicle on which the clamping attachment is installed. The vehicle&#39;s hydraulic system  52  includes a reservoir  56  for hydraulic fluid and a pump  58 , typically driven by an internal combustion engine or electric motor (not shown), to supply pressurized hydraulic fluid to the attachment and the other hydraulically operated equipment of the vehicle. A relief valve  60  limits the pressure in the vehicle&#39;s hydraulic circuit. A load handling vehicle&#39;s hydraulic circuit also typically includes plural valves to control the flow of pressurized fluid from the pump to the various actuators of the vehicle and, thereby, control the operation of the vehicle&#39;s hydraulically operated functions. A lift truck, for example, typically includes a lift/lower spool valve (not shown) that controls raising and lowering of a carriage in the lift truck&#39;s mast  26  and a tilt spool valve (not shown) which controls the forward and backward tilting of the mast. 
     The exemplary load handling vehicle hydraulic circuit  52  also includes plural auxiliary spool valves  62 ,  64  which are connectable to the hydraulic circuitry of an attachment, such as the clamping attachment  22 , mountable on the vehicle. In the exemplary vehicle hydraulic circuit  52 , the auxiliary spool valves  62 ,  64  are three position, open center valves with slidable spools which are manually operable  66  and centered by springs  68 . However, the auxiliary spool valves could be operated by electric solenoids or other electrical or hydraulic actuators or remote control devices. A first auxiliary spool valve  64  is connected to an exemplary hydraulic motor  70  by a first conduit  72  and a second conduit  74 . The hydraulic motor  70  may, for example, power rotation the exemplary clamping attachment  22  but could be any hydraulic actuator and arranged to operate another device. When the first auxiliary spool valve  64  is centered, as it is illustrated, the conduits  72 ,  74  connecting the valve to the motor  70  are blocked and the motor is inoperative. Pressurized fluid flowing from the pump  58 , in conduit  76 , passes through open passages in the second auxiliary spool valve  62 , through the conduit  77  and the first auxiliary spool valve  64  and returns to the reservoir  56 . When the spool of the first auxiliary spool valve  64  is shifted to the right from the illustrated position, fluid under pressure in conduits  76  and  77  will flow through the first spool valve into the conduit  72  and then to the motor  70  causing the motor to rotate in a first direction. Fluid exiting the motor returns through conduit  74  and thereafter to the reservoir  56  through conduit  78 . When the spool of the first auxiliary spool valve  64  is shifted to the left, pressurized fluid is transmitted from conduits  76  and  77  to conduit  74  to cause the motor to rotate in the opposite direction. Fluid exhausted from the motor  70  passes through conduit  72  to conduit  78  and returns to the reservoir  56 . 
     When the second auxiliary spool valve  62  is centered, conduits  80  and  86  are blocked and pressurized fluid from the pump flows through the open center passage in the valve and through conduit  77  to the first auxiliary spool valve  64 . 
     When the second auxiliary spool valve  62  is shifted to the right from the position illustrated, pressurized fluid from the pump  58  is transmitted through the second auxiliary spool valve to conduit  80 . Pressurized fluid is communicated through a check valve  94 , conduit  82  and the load check valves  96  to the piston end volumes  90  of the actuators  36 . The piston end volumes  90  defined by the interior volumes of the actuator bodies  38  and the ends of the pistons  98  distal of the cylinder rods  42  are connected in parallel by through conduit  82 . Pressurized fluid in the piston end volumes  90  of the actuators  36  urges the pistons to move; expelling fluid from the rod end volumes  92  of the actuators and extending the cylinder rods. The rod end volumes  92  of the actuators  36  which are defined by portions of the interior volumes of the actuator bodies  38 , the cylinder rods  42  and the exposed portion of the rod side of the pistons  98  are connected in parallel by conduit  84 . 
     However, the flow of fluid from the rod end volumes  92  is blocked initially by the check valve  100  located between the conduit  84  and the conduit  86  and by a normally closed modulating valve  102  blocking flow between conduit  84  and conduit  82 . The modulating valve  102  has a first pilot connection  104  to the conduit  84  and a second pilot connection  106  to the conduit  86 . When the pressure in the rod end volumes  92 , the conduit  84  and the pilot connection  104  increases and the pressure in the pilot connection  106  is low, the modulator valve will open enabling the fluid under pressure in the rod end volumes  92  of the actuators  36  to flow through the conduit  84  and combine with the fluid from the pump  58  flowing through conduit  82  and into the piston end volumes  90  of the actuators. The pressure in the conduit  86  will remain low when the second spool valve is shifted to the right because the conduit  86  is in fluid communication with the reservoir  56  and the check valve  100  blocks any flow fluid into the conduit from the rod end volumes of the actuators. 
     The speed at which the clamp arm  30  moves is substantially increased because the fluid transferred from the rod end volume  92  combines with the fluid supplied by the vehicle&#39;s pump to the piston end volumes  90  of the actuators  36 . On the other hand, since the rod end volumes  92  and the piston end volumes  90  of the hydraulic actuators  36  are in fluid communication, the fluid pressure on both sides of the actuators&#39; pistons equalizes and the effective areas of the pistons  98  of the hydraulic actuators are the areas of the cross-sections of the actuator rods  42 . The maximum clamping force that can be exerted by an actuator is equal to product of the area of the actuator rod cross-section and the maximum pressure in the actuator which is a fraction of the force produced when the maximum pressure is applied to the full area of the piston. The maximum pressure in the clamping attachment&#39;s hydraulic circuit is controlled by the one of the vehicle&#39;s relief valve  60  and the clamping attachment&#39;s bidirectional relief valve  110  having the lowest relief pressure. 
     When the load is clamped and the operator releases the manual control  66  for the second auxiliary spool valve  62 , the spring  68  returns the valve&#39;s spool to the center position blocking conduits  80  and  86 . Clamping pressure is maintained in the piston end volumes  90  of the hydraulic actuators  36  by load check valves  96  which prevent the flow of fluid from the piston ends of the actuators. If a clamp arm should strike another object raising the pressure in the rod end volumes  92  of the actuators  36 , the clamping force will be maintained because fluid flow out of the piston end volumes  90  and the rod end volumes  92  of the actuators would be blocked by check valve  94  even if a load check valve  96  and the modulating valve  102  should momentarily open in response to higher pressure in the rod end volume of the actuator and low pressure in conduit  86 . 
     To open the clamp arms and release a clamped load, the operator shifts the second auxiliary spool valve  62  to the left, from the center position illustrated in  FIG. 3 . This will direct pressurized fluid from the pump  58  into conduit  86  and through the check valve  100 . Pressure is applied to the fluid in conduit  84  but the modulator valve  102  will remain closed, blocking the flow of fluid into conduit  82  because the pressure at the second pilot connection  106  will be high. As pressure increases in the rod end volumes  92  of the actuators  36 , the pilot operated load check valves  96  are forced open by their pilot operators in response to pressure in pilot connections  112 . In addition, the pilot operator of the check valve  94  will be subjected to the pressure of the fluid in the rod end volumes of actuators and will open the check valve. With the load check valves and check valve  94  open, fluid will be expelled from the piston end volumes  90  of the actuators by movement of the pistons and flow back to the reservoir  56  through conduits  82 ,  80 ,  77  and  78 . Since the full output of the pump flows into the rod end volumes of the actuators at pressures as high as the relief pressure, the actuators can move the open clamp arm through its full range with the same speed and force as they would with a non-regenerative hydraulic circuit. 
     The regenerative hydraulic circuit substantially increases the clamping speed while substantially reducing the clamping force of the arms of the clamping attachment to protect the load while maintaining the opening force and speed of the attachment and avoiding the need to design, manufacture and stock special hydraulic actuators. 
     The detailed description, above, sets forth numerous specific details to provide a thorough understanding of the present invention. However, those skilled in the art will appreciate that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuitry have not been described in detail to avoid obscuring the present invention. 
     All the references cited herein are incorporated by reference. 
     The terms and expressions that have been employed in the foregoing specification are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims that follow.