Patent Publication Number: US-2023136144-A1

Title: Smart Clamp with Base-side Blocking Valve

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of International Application No. PCT/US21/21420, filed 2021 Mar. 8, which claims the benefit of U.S. Provisional Application No. 62986767, filed 2020 Mar. 8, and U.S. Provisional Application No. 63043776, filed 2020 Jun. 24, all incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to cargo handling equipment. More particularly, the present invention relates to load clamps for use primarily with lift trucks. 
     BACKGROUND 
     Material handling vehicles such as lift trucks are used to pick up and deliver loads between stations. A typical lift truck  10  has a mast  12 , which supports a carriage  14  that can be raised along the mast  12  (see  FIG.  1   ). The carriage  14  typically has one or more carriage bars  16  to which a fork frame  18  is mounted. The carriage bars  16  are coupled to the mast in a way that allows the lift truck  10  to move the carriage bars  16  up and down, but not laterally relative to the truck. The fork frame  18  carries a pair of forks  20 . An operator of the lift truck  10  maneuvers the forks  20  beneath a load prior to lifting it. 
     Instead of forks  20 , a lift truck  10  may have other kinds of attachments coupled to its mast  12 . One type of attachment is a clamp load handler  32  (See  FIG.  2   ). The clamp load handler  32  typically comprises a frame  40 , one or more actuators  36  and two clamp arms  34 . The actuators  36  are configured to move the clamp arms  34  toward or away from each other with actuator rods  38 . The clamp arms  34  typically have a gripping material on the inside surfaces that contact the load. The gripping material, such as rubber or polyurethane, provides high friction contact surface for gripping the load and also provides a compressible and resilient contact surface to protect the load from superficial damage from the clamp arms  34 . In use, the operator of the lift truck  10  approaches a load to be carried, such as a stack of cartons or a large appliance, such as a refrigerator. As the lift truck  10  approaches the load, the operator uses controls to open the gap between the clamp arms  34  wider than the load and may adjust the height of the clamp arms  34  so they will engage the load in a suitable location. The operator then maneuvers the lift truck  10  to straddle the load between the clamp arms  34 . When the clamp arms  34  are positioned suitably around the load, the operator uses controls to bring the clamp arms  34  together, grasping the load. The operator then uses other controls to raise the load clamp assembly  22 , raising the load off the floor, the load held between the clamp arms  34  by friction. The operator then drives the load to a desired location. The amount of force the clamp arms  34  apply must be “just right.” Too little force and the load may slip out of the clamp arms  34 , which can be disastrous, particularly when the lift truck  10  is moving. Too much force can crush the load. With only manual control of the clamp arms  34 , applying just the right amount of force is completely dependent on the lift truck operator. Even a skilled operator&#39;s ability to apply just the right amount of force is limited because they cannot feel the amount of force being applied and must rely on visual and audio indications of how much force is being applied. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described by way of representative embodiments, illustrated in the accompanying drawings in which like references denote similar elements, and in which: 
         FIG.  1    is an isometric view of a prior art lift truck, illustrating typical components of a lift truck  10  equipped with forks  20 . 
       FIG. 2  is an isometric view of a prior art lift truck  10 , illustrating typical components of a lift truck  10  equipped with a load clamp assembly  22 . 
         FIG.  3    shows a perspective view of the main structural components of a first representative embodiment smart clamp load handler  104  (hydraulic lines and electrical controls not shown). 
         FIG.  4 A  shows a schematic of a first representative embodiment smart clamp system  100  in a fully open phase of operation (before time 0 in  FIG.  5   ). 
         FIG.  4 B  shows a schematic of a first representative embodiment smart clamp system in a closing phase of operation (time 0 to time  302  in  FIG.  5   ). 
         FIG.  4 C  shows a schematic of a first representative embodiment smart clamp system  100  in an equalization phase of operation (time  302  to time  303  in  FIG.  5   ). 
         FIG.  4 D  shows a schematic of a first representative embodiment smart clamp system  100  at the end of the equalization phase of operation (at time  303  in  FIG.  5   ). 
         FIG.  4 E  shows a schematic of a first representative embodiment smart clamp system  100  in a force adjustment clamping phase of operation (time  303  to time  304  in  FIG.  5   ). 
         FIG.  4 F  shows a schematic of a first representative embodiment smart clamp system  100  in a clamped phase of operation (time  304  to time  305  in  FIG.  5   ). 
         FIG.  4 G  shows a schematic of a first representative embodiment smart clamp system  100  in an opening of operation in which the clamp arms release and move away from the load. 
         FIG.  5    shows a graph over time of the forces generated by the first representative embodiment smart clamp system  100  during clamping operations. 
         FIG.  6 A  shows a schematic of a second representative embodiment smart clamp system  400  in an equalization phase of operation (time  302  to time  403  in  FIG.  6 C ). 
         FIG.  6 B  shows a schematic of a second representative embodiment smart clamp system  400  in a slow adjustment phase of operation (time  403  to time  404  in  FIG.  6 C ). 
         FIG.  6 C  shows a graph over time of the forces generated by the second representative embodiment smart clamp system  400  during clamping operation. 
         FIG.  7    shows a schematic of a third representative embodiment smart clamp system  500  in a force adjustment phase of operation. 
         FIG.  8    shows a schematic of a fourth representative embodiment smart clamp system  600  in an equalization phase of operation. 
         FIG.  9 A  shows a schematic of the fifth representative embodiment smart clamp system  700  in a closing phase of operation (time 0 to time  302  in  FIG.  9 D ). 
         FIG.  9 B  shows a schematic of a fifth representative embodiment smart clamp system  700  in an equalization phase of operation (time  302  to time  403  in  FIG.  9 D ). 
         FIG.  9 C  shows a schematic of a fifth representative embodiment smart clamp system  700  in a slow adjustment phase of operation (time  403  to time  404  in  FIG.  9 D ). 
         FIG.  9 D  shows a graph over time of the forces generated by the fifth representative embodiment smart clamp system  700  during clamping operations. 
     
    
    
     DETAILED DESCRIPTION 
     Before beginning a detailed description of the subject invention, mention of the following is in order. When appropriate, like reference materials and characters are used to designate identical, corresponding, or similar components in different figures. 
     In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the developer&#39;s specific goals, such as compliance with application and business-related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure. 
     Use of directional terms such as “upper,” “lower,” “above,” “below”, “in front of,” “behind,” etc. are intended to describe the positions and/or orientations of various components of the invention relative to one another as shown in the various figures and are not intended to impose limitations on any position and/or orientation of any embodiment of the invention relative to any reference point external to the reference. Herein, “left” and “right” are from the perspective of an operator seated in a lift truck facing the carriage of the lift truck. Herein, “lateral” refers to directions to the left or the right and “longitudinal” refers to a direction perpendicular to the lateral direction and to a plane defined by the carriage. 
     Those skilled in the art will recognize that numerous modifications and changes may be made to the various embodiments without departing from the scope of the claimed invention. It will, of course, be understood that modifications of the invention, in its various aspects, will be apparent to those skilled in the art, some being apparent only after study, others being matters of routine mechanical, chemical and electronic design. No single feature, function or property of the first embodiment is essential. Other embodiments are possible, their specific designs depending upon the particular application. As such, the scope of the invention should not be limited by the particular embodiments herein described but should be defined only by the appended claims and equivalents thereof. 
     First Representative Embodiment—Structure 
       FIG.  3    shows a perspective view of the main structural components of a first representative embodiment smart clamp load handler  104 . The smart clamp load handler  104  comprises a frame  202 , a pair of clamp arms  204 ,  205  coupled to the frame  202  and a pair of clamp actuators  152 ,  154 . A first clamp actuator  152  is coupled to a first clamp arm  204  and a second clamp actuator  154  coupled to a second clamp arm  205 . The clamp actuators  152 ,  154  are configured to pull the clamp arms  204 ,  205  together or push them apart. 
     The frame  202  is configured to be coupled to a carriage  14  of a lift truck  10 . The frame  202  comprises two frame vertical beams  226  with four guide channels  206  coupled thereto. Two guide channels  206  are positioned near a top of the frame  202  and two guide channels  206  are positioned near a bottom of the frame  202 . In the first representative embodiment smart clamp load handler  104 , the upper two guide channels  206  share a common channel wall and the lower two guide channels  206  are similar. However, in other embodiments, the guide channels  206  do not necessarily have common walls with adjacent guide channels  206 , the frame  202  may have more or fewer guide channels  206  and the guide channels may be arranged differently. 
     Each of the guide channels  206  has a guide channel cavity  208 . The guide channels  206  each have a guide channel slot  240  on the front, opening to the guide channel cavity  208 . Each guide channel  206  has a channel bearing, positioned inside the guide channel cavity  208  and shaped to conform thereto, and with its own interior cavity that is similarly shaped, but slightly smaller. The channel bearing is detachably coupled to the guide channel  206 . The channel bearings are made of suitable bearing material that provides low friction and is softer than the components it has sliding contact with in order to preferentially wear. Since the channel bearings are removable, they can be easily replaced when worn down. 
     Each clamp arm  204 ,  205  has two clamp sliding beams  218  coupled thereto. The two clamp sliding beams  218  are configured to slidingly fit into two of the guide channels  206  of the frame  202 . More specifically, the clamp sliding beams  218  insert into the channel bearings of the guide channels  206  with a sliding fit. In the representative embodiment, the portion of each clamp sliding beam  218  inserted into the guide channel  206  has a “T” cross-section, with the top of the “T” held inside the guide channel  206  and the base of the “T” extending out of the guide channel slot  240 . However, in other embodiments, the guide channel  206  and the clamp sliding beam  218  may have other suitable cross-sectional shapes. 
     Two actuator brackets  232  are coupled to the frame  202 , one coupled to a bottom of a lower of the top two guide channels  206 , and the other coupled to a top of an upper of the bottom two guide channels  206 . The upper actuator bracket  232  is position on the left of the frame  202  and the lower actuator bracket  232  is located on the right of the frame  202 , when viewed from the lift truck  10 . Each of the clamp actuators  152 ,  154  is coupled to the frame  202  via one of the actuator brackets  232 . Each clamp actuators  152 ,  154  has an actuator rod  140  that is coupled to an actuator bracket  232  on one of the clamp arms  204 ,  205 . 
     Coupled to the frame  202  are a controller  120 , a control console  174 , and a hydraulic manifold  260 . The controller  120  and control console  174  are described in detail elsewhere herein. The hydraulic manifold  260  has several valves, described in detail elsewhere herein. 
       FIGS.  4 A- 4 G  each show a schematic view of a first representative embodiment of a smart clamp system  100 , each in a different phase of operation for clamp and unclamping a load  50 . The schematic is divided with truck side  102  components of the smart clamp system  100  on the left and load-handler side  103  components on the right. A first clamp hydraulic line  144  and a second clamp hydraulic line  146  cross over from the truck side  102  to the load-handler side  103  via flexible connections that have sufficient slack to handle the relative motion between the smart clamp load handler  104  and the lift truck  10 . The smart clamp system has a control console  174  mounted on the lift truck  10 . In some embodiments the control console  174  is mounted on the smart clamp load handler  104 . In yet other embodiments, there is a first control console  174  on the lift truck  10  and a second control console  174  on the smart clamp load handler  104 , each have some or all of the functions of the other. 
     On the truck side  102  of the schematic, the smart clamp system  100  has a hydraulic pump  106  to supply pressurized hydraulic fluid. The hydraulic pump  106  draws hydraulic fluid out of a hydraulic fluid reservoir  138 . The hydraulic pump  106  is typically powered by the main engine of the lift truck  10  by belt or gear drives. The hydraulic pump  106  is typically a positive displacement pump. The outlet of the hydraulic pump  106  is connected to a relief valve  108  which regulates the pressure produced by the hydraulic pump  106  and provides a discharge path for excess hydraulic fluid that is not needed for the moment by the smart clamp system  100 . The output of the hydraulic pump  106  couples to a truck hydraulic feed line  124 . A truck hydraulic return line  126  brings hydraulic fluid back to the hydraulic fluid reservoir. 
     The smart clamp system  100  comprises a directional control valve  128 , typically mounted as standard equipment to the lift truck  10 . The directional control valve  128  is manually operated, but in some embodiments the directional control valve  128  may be a solenoid operated valve controlled by the controller  120  on the load-handler side  103  or a different controller on the truck side  102 . The directional control valve  128  controls the direction of hydraulic fluid flow, which determines whether the clamp actuators  152 ,  154  move the clamp arms  204 ,  205  to open or to close. The directional control valve  128  is a three position, four port valve. When the directional control valve  128  is in a closed position, all four ports are blocked. When the directional control valve  128  is in a straight through position, a first input port of the directional control valve  128  (connected to the truck hydraulic feed line  124 ) is ported through a first output port to a first clamp hydraulic line  144 , while a second input port of the directional control valve  128  (connected to the truck hydraulic return line  126 ) is ported through a second output port to the second clamp hydraulic line  146 . When the directional control valve  128  is in a cross-over position, the first input port of the directional control valve  128  (connected to the truck hydraulic feed line  124 ) is ported through the second output port to the second clamp hydraulic line  146  and the second input port (connected to the truck hydraulic return line  126 ) is ported through the first output port to the first clamp hydraulic line  144 . In other embodiments, the output ports could be swapped so that when the directional control valve  128  is in a cross-over position, the first input port of the directional control valve  128  (connected to the truck hydraulic feed line  124 ) is ported through the first output port to the first clamp hydraulic line  144 , etc. and operations would be swapped as well. 
     On the load-handler side  103  of the schematic, the two clamp arms  204 ,  205  and the associated clamp actuators  152 ,  154  from  FIG.  3    are shown. The clamp actuators  152 ,  154  are hollow tubes with capped ends, each having an actuator piston  142  inside coupled to an actuator rod  140  that passes through a sealed opening in one of the capped ends. Each of the clamp actuators  152 ,  154  is thus divided by the actuator piston  142  into a rod-side on which the actuator rod  140  is coupled to the actuator piston  142  and a base-side opposite. Each of the clamp actuators  152 ,  154  is thus divided into a rod-side chamber through which the actuator rod  140  passes and a base-side chamber opposite. In the first representative embodiment smart clamp system  100 , the rod-side chamber is the opening chamber—the chamber that opens the clamp arms  204 ,  205  when hydraulic fluid is applied and the base-side is the closing chamber. However, in other embodiments, the base-side chamber may be the opening chamber, such as if the actuators  152 ,  154  were mounted outboard of the clamp arms  204 ,  205  and pushed to close them. The smart clamp load handler  104  also comprises a base-side control valve  160 , a base-side blocking valve  162 , a regeneration valve  164 , an input pressure sensor  130 , a rod-side pressure sensor  132 , a first base-side pressure sensor  168 , a second base-side pressure sensor  170 , a main rod-side hydraulic line check valve  172 , a first base equalization valve  134 , a second base equalization valve  136  and a controller  120 . In some alternative embodiments, one or more of these components may be located on the truck side  102 . 
     The load-handler side  103  of the smart clamp system  100  has a main rod-side hydraulic line  148  and a main base-side hydraulic line  150 . The main rod-side hydraulic line  148  splits into a first rod-side hydraulic line  180  and a second rod-side hydraulic line  182  (these three are collectively referred to as the “rod-side hydraulic lines”). The main base-side hydraulic line  150  splits into a first base-side hydraulic line  184  and a second base-side hydraulic line  186  (these three are collectively referred to as the “base-side hydraulic lines”). The first rod-side hydraulic line  180  hydraulically couples to the rod-side of the first clamp actuator  152 , the second rod-side hydraulic line  182  hydraulically couples to the rod-side of the second clamp actuator  154 , the first base-side hydraulic line  184  hydraulically couples to the base-side of the first clamp actuator  152 , and the second base-side hydraulic line  186  hydraulically couples to the base-side of the second clamp actuator  154 . 
     The base-side control valve  160 , the base-side blocking valve  162 , and the regeneration valve  164  are configured to stop the clamping operation when the controller  120  decides to do so based on its sensor input and logic/programming. The base-side control valve  160 , the base-side blocking valve  162 , and the regeneration valve  164  are solenoid operated, powered and controlled by the controller  120  over control wiring  112 . 
     The base-side control valve  160  is a two position, two port valve with one input port and one output port. When in a first position (flow unblocked as shown in  FIG.  4 A ), the base-side control valve  160  hydraulically couples the input port (connected to the first clamp hydraulic line  144 ) with the output port (connected to a main base-side hydraulic line  150 ). When in a second position (check valve as shown in  FIG.  4 D ), the base-side control valve  160  hydraulically couples the input port (connected to the first clamp hydraulic line  144 ) with the output port (connected to the main base-side hydraulic line  150 ), but only allows flow from the first clamp hydraulic line  144  to the main base-side hydraulic line  150 , but not in the reverse direction. In the first representative embodiment smart clamp system  100 , the base-side control valve  160  is a poppet valve that in its first position it allows high flow, while in its second position it blocks flow with low leakage (less than would a spool valve). 
     The base-side blocking valve  162  is a two position, two port valve with one input port and one output port. When in a first position (flow blocked as shown in  FIG.  4 D ), the base-side blocking valve  162  hydraulically blocks flow between the input port (connected to the first clamp hydraulic line  144 ) and the output port (connected to the main base-side hydraulic line  150 ). When in a second position (flow unblocked as shown in  FIG.  4 E ), the base-side blocking valve  162  hydraulically couples the input port (connected to the first clamp hydraulic line  144 ) with the output port (connected to the main base-side hydraulic line  150 ). In the first representative embodiment smart clamp system  100 , the base-side blocking valve  162  is a poppet valve, so when in the first position, it blocks flow with low leakage (less than would a spool valve) and when in the second position it allows low flow that can be modulated proportionally and with high accuracy. In some embodiments, the base-side blocking valve  162  in the second position only allows flow from the main base-side hydraulic line  150  to the first clamp hydraulic line  144 , but not the reverse. In other embodiments, the base-side blocking valve  162  and the base-side control valve  160  may be replaced with a single three position poppet valve that in its first position is high flow and non-proportional, while in its second position it blocks flow with low leakage (less than would a spool valve) and when in its third position allows low flow that can be modulated proportionally with high accuracy. In other embodiments, the base-side control valve  160  is omitted and its functions taken over by the base-side blocking valve  162 . In such a system, the clamp arms  204 ,  205  would move slower, particularly in the closing and opening phases of operation. In other embodiments, the base-side blocking valve  162  is a simple two-position valve with no modulation and an orifice in series to slow flow. In other embodiments, the base-side blocking valve  162  is a multi-position valve, with multiple flow positions in addition to the no flow position, each flow position with a different passage or orifice size. 
     The regeneration valve  164  is a two position, two port valve with one input port and one output port. When in a first position (flow blocked as shown in  FIG.  4 B ), the regeneration valve  164  hydraulically blocks all flow between its input port (connected to the main rod-side hydraulic line  148 ) and its output port (connected to the main base-side hydraulic line  150 ). When in a second position (flow unblocked as shown in  FIG.  4 C ), the regeneration valve  164  hydraulically couples the input port (connected to the main rod-side hydraulic line  148 ) with the output port (connected to the main base-side hydraulic line  150 ). In the smart clamp system  100 , the regeneration valve  164 , like the base-side blocking valve  162 , is a poppet valve, so when in the first position, it blocks flow with low leakage (less than would a spool valve) and when in the second position it allows low flow that can be modulated proportionally with high accuracy. In some embodiments, the regeneration valve  164  in the second position ofnly allows flow from the main rod-side hydraulic line  148  to the main base-side hydraulic line  150 , but not the reverse. In other embodiments, the regeneration valve  164  is a simple two-position valve with no modulation and an orifice in series to slow flow. 
     The main rod-side hydraulic line check valve  172  is a pilot operated check valve connecting the second clamp hydraulic line  146  with the main rod-side hydraulic line  148  and with a pilot tube to the first clamp hydraulic line  144 . The main rod-side hydraulic line check valve  172  allows flow from the second clamp hydraulic line  146  to the main rod-side hydraulic line  148  in all circumstances, but only allows flow from the main rod-side hydraulic line  148  to the second clamp hydraulic line  146  if the pressure in the first clamp hydraulic line  144  is sufficient to cause the pilot operated check valve to lift. In the first representative embodiment smart clamp system  100 , the main rod-side hydraulic line check valve  172  lifts if the pressure of the first clamp hydraulic line  144  is equal to or greater than ⅓ of the combined pressure of the second clamp hydraulic line  146  and the main rod-side hydraulic line  148 . The main rod-side hydraulic line check valve  172  primarily serves to prevent pressurized hydraulic fluid in the main rod-side hydraulic line  148  from leaking out through the directional control valve  128  when it is in a neutral, (supposedly) no-flow position. However, there is usually some leakage through a typical directional control valve  128  when in a neutral position. Some alternative embodiments may omit the main rod-side hydraulic line check valve  172  if the smart clam load handler is to be used with a directional control valve  128  that has no or very minimal leakage when in the neutral position. 
     The first base equalization valve  134  is a differential pilot operated relief valve that has an input port coupled to the second base-side hydraulic line  186  and an output port coupled to the first base-side hydraulic line  184 . The first base equalization valve  134  helps keep the movement of the clamp arms  204 ,  205  equal. The first base equalization valve  134  has a first pilot line that couples to the first base-side hydraulic line  184  and a second pilot line that couples to the second base-side hydraulic line  186 . The first base equalization valve  134  is configured to block flow in its normal position and configured to open if the pressure in the second base-side hydraulic line  186  exceeds the pressure in the first base-side hydraulic line  184  by a predetermined amount. The predetermined amount it adjustable. 
     The second base equalization valve  136  is a differential pilot operated relief valve that has an input port coupled to the first base-side hydraulic line  184  and an output port coupled to the second base-side hydraulic line  186 . The second base equalization valve  136  helps keep the movement of the clamp arms  204 ,  205  equal. The second base equalization valve  136  has a first pilot line that couples to the second base-side hydraulic line  186  and a second pilot line that couples to the first base-side hydraulic line  184 . The second base equalization valve  136  is configured to block flow in its normal position and configured to open if the pressure in the first base-side hydraulic line  184  exceeds the pressure in the second base-side hydraulic line  186  by a predetermined amount. The predetermined amount it adjustable. 
     In the first representative embodiment smart clamp system  100 , the first base equalization valve  134  and second base equalization valve  136  are combined in a single package as a dual equalization valve. In some alternative embodiments, the first base equalization valve  134  and the second base equalization valve  136  are omitted. In other embodiments, the first base equalization valve  134  and the second base equalization valve  136  are replaced with a different mechanism for equalizing pressure between the first base-side hydraulic line  184  and the second base-side hydraulic line  186 . 
     The smart clamp system  100  has a flow divider  176  between the main base-side hydraulic line  150  and the base-side hydraulic line  184 ,  186 . The flow divider  176  divides the flow equally between the first base-side hydraulic line  184  and the second base-side hydraulic line  186 . The flow divider  176  helps keep the movement of the clamp arms  204 ,  205  equal. 
     The pressure sensors  130 ,  132 ,  168 ,  170  provide pressure measurements over control wiring  112  to the controller  120  for use in controlling the smart clamp load handler  104 . The rod-side pressure sensor  132  is coupled to the main rod-side hydraulic line  148  downstream (towards the second clamp actuator  154 ) of the main rod-side hydraulic line check valve  172  and upstream (towards the hydraulic pump  106 ) of the second clamp actuator  154 . The input pressure sensor  130  is coupled to the second clamp hydraulic line  146  downstream (towards the second clamp actuator  154 ) of the directional control valve  128  and upstream (towards the hydraulic pump  106 ) of the main rod-side hydraulic line check valve  172 . The first base-side pressure sensor  168  is coupled to the first base-side hydraulic line  184  downstream (towards the first clamp actuator  152 ) of the flow divider  176 , upstream (towards the hydraulic pump  106 ) of the first clamp actuator  152  and preferentially upstream of the base equalization valves  134 ,  136 . The second base-side pressure sensor  170  is coupled to the second base-side hydraulic line  186  downstream (towards the second clamp actuator  154 ) of the flow divider  176 , upstream (towards the hydraulic pump  106 ) of the second clamp actuator  154 , and preferentially as close to the clamp actuators  152 ,  154  as possible. 
     In the first representative embodiment smart clamp system  100 , the pressure sensors  130 ,  132 ,  168 ,  170  are pressure transducers that output a 4-20 mA signal that is converted in the controller  120  to a 0-3.3V signal that is interpreted by an analog to digital converter in the controller  120 . Specifically, 0-3000 PSI (Hydraulic) translates to 0-5V transducer output, which is converted to 0-3.3V in the controller  120 , which is converted to 0-2048 points by the analog to digital converter, which is interpreted as 0-3000 PSI in the microcontroller of the controller  120 . 
     The controller  120  is configured with programming to control movement of the clamp arms  204 ,  205  and the force applied by them. The controller  120  programming is configured to change the positions of the valves  160 ,  162 ,  164  based on inputs from the pressure sensors  130 ,  132 ,  168 ,  170 . The controller  120  is configured to have the first representative embodiment smart clamp system  100  apply multiple target levels of force to a load  50 . The target levels may be set by authorized personnel, such as a facility manager, so that operators can only clamp to the levels of force programmed into the controller  120 . In the representative embodiment, the controller  120  comprises a micro-controller architecture, but in alternative embodiments, the controller  120  may comprise hard-wired logic based, for example, on relays and/or transistors. In yet other embodiments, the controller  120  may comprise hydraulic logic utilizing hydraulic components, and utilizing a hydraulic working fluid such as air or oil. The control wiring  112  would then be hydraulic control lines instead of electrical conductors and the various automated valves would be hydraulically operated rather than solenoid operated. 
     The control console  174  has an electronic graphical touch screen display that shows various information regarding operation of the smart clamp system  100 , including pressure, clamp force, indication of when the load is clamped and when the load is under-clamped. In some embodiments, the controller  120  has an electronic graphical touch screen display in addition or instead of the control console  174 . The electronic graphical touch screen display is positioned to be visible to the operator when the smart clamp load handler  104  is at ground level or raised by the lift truck mast  12 . In some embodiments the electronic graphical touch screen display is physically separate from, but communicatively coupled with the controller  120  and relocatable on the smart clamp load handler  104  to ensure visibility. 
     In some alternative embodiments, the flow divider  176 , the second base-side pressure sensor  170 , and the base equalization valves  134 ,  136  are omitted and there is only the first base-side pressure sensor  168 , coupled to the main base-side hydraulic line  150 . 
     In some alternative embodiments, the base-side pressure sensors  168 ,  170  and the rod-side pressure sensor  132  may be replaced by a differential pressure sensor that measures differential pressure from the base-side to the rod-side (See differential pressure sensor  502  in  FIG.  7   ). In some alternative embodiments, the differential pressure sensor can be replaced with one or more pressure switches. Each pressure switch would trigger repositioning of one or more of the valves  160 ,  162 ,  164  to a particular state, either directly or via controller  120  logic/programming. 
     In some alternative embodiments, the clamp actuators  152 ,  154  each have a load cell coupled thereto. The load cells measure the force applied by each of the clamp actuators  152 ,  154 , which may be used to control operation of the first representative embodiment smart clamp system  100  in a similar manner to embodiments using forces calculated based on the base-side pressure sensors  168 ,  170  and the rod-side pressure sensors  132 . 
     In some alternative embodiments, one or more frame deflection sensors are coupled to the frame  202  or to one or more clamp sliding beams  218  of the smart clamp load handler  104 . The frame deflection sensors measure the deflection of the frame  202  caused by the force applied by each of the clamp actuators  152 ,  154 , to the load  50 , which may be used calculate the force on the load  50  control operation of the first representative embodiment smart clamp system  100  in a similar manner to embodiments using forces calculated based on the base-side pressure sensors  168 ,  170  and the rod-side pressure sensors  132 . 
     In some alternative embodiments, the smart clamp load handler  104  has an orifice coupled between the first clamp hydraulic line  144  and the second clamp hydraulic line  146 . This allows pressure to equalize between these two hydraulic lines when the directional control valve  128  is in a fully blocked position and equalize at a pressure below what is applied by the hydraulic pump  106  when the directional control valve  128  is in its straight flow or cross flow positions. This also gives additional volume into which hydraulic fluid can bleed when the first representative embodiment smart clamp system  100  is in a force adjustment phase. In some alternative embodiments, an additional pressure sensor, similar to the input pressure sensor  130 , is coupled to the first clamp hydraulic line  144 , to assist the controller  120  in determining flow direction. In some alternative embodiments, the orifice is replaced with a flow meter, which has a similar flow restricting quality, but will also provide an indication of the direction of flow to the controller  120  that can be used to determine which of the clamp hydraulic line  144 ,  146  has hydraulic pressure applied (i.e., the position of the directional control valve  128 ). 
     In some alternative embodiments, one of the clamp actuators  152 ,  154  may be omitted. In such embodiments, only one of the clamp arms  204 ,  205  moves and the other is fixed. In other alternative embodiments, one of the clamp arms  204 ,  205  moves under direct action of the actuator and the other moves by some mechanism that forces it to mirror the movements of the other clamp arm  204 ,  205 . In single actuator embodiments, the flow divider  176  is also omitted, as are all the components between the flow divider  176  and the clamp actuators  152 ,  154 . 
     First Representative Embodiment—Method of Operation 
       FIG.  5    shows a graph over time of the forces generated by the first representative embodiment smart clamp system  100  during clamping operations. The rod force line  320 , calculated from pressure readings from the rod-side pressure sensor  132 , traces the force on the rod-side of one of the actuator pistons  142  by hydraulic fluid pressure in the rod-side of one of the clamp actuators  152 ,  154 . The base force left line  322 , calculated from pressure readings from the first base-side pressure sensor  168 , traces the force on the base-side of the actuator piston  142  by hydraulic fluid pressure in the base-side of the first clamp actuator  152 . The base force right line  324 , calculated from pressure readings from the first base-side pressure sensor  168 , traces the force on the base-side of the actuator piston  142  by hydraulic fluid pressure in the base-side of the second clamp actuator  154 . The absolute force line  326 , calculated as the rod force minus the average of the two base forces, traces the force put on the load  50  by each of the clamp arms  204 ,  205 . The input force equivalent line  328  is calculated as the input pressure (from the input pressure sensor  130 ) times the rod-side piston area of one of the clamp actuators  152 ,  154 . It traces the amount of potential force available in the second clamp hydraulic line  146 , if the pressure there were present in the rod-side of one of the clamp actuators  152 ,  154 . 
       FIG.  4 A  shows a schematic of the first representative embodiment smart clamp system  100  in a fully open phase of operation (before time 0 in  FIG.  5   ). The clamp arms  204 ,  205  are fully open and not in contact with the load  50 . The directional control valve  128  is in a closed position with all four ports blocked. The base-side control valve  160  is first position (flow unblocked), the base-side blocking valve  162  is in its first position (flow blocked), and the regeneration valve  164  is in its first position (flow blocked). 
       FIG.  4 B  shows a schematic of a first representative embodiment smart clamp system in a closing phase of operation (time 0 to time  302  in  FIG.  5   ). The closing phase of operation is commenced with the directional control valve  128  being put (usually by a human operator, but in some embodiments, by an electrical controller or other automated controller) in its cross-over position. Pressurized hydraulic fluid from the truck hydraulic feed line  124  flows into the second clamp hydraulic line  146 , through the main rod-side hydraulic line check valve  172 , through the main rod-side hydraulic line  148 , through the first rod-side hydraulic line  180  and second rod-side hydraulic line  182  into the rod side of the first clamp actuator  152  and second clamp actuator  154 . Hydraulic pressure builds in the rod side of the clamp actuators  152 ,  154 , measured by the rod-side pressure sensor  132 , until enough force is generated to overcome friction and the actuator pistons  142  move inward, moving the clamp arms  204 ,  205  towards each other and toward the load  50  ( FIG.  5   , time 0). Hydraulic fluid is forced out of the base side of the first clamp actuator  152  into the first base-side hydraulic line  184  and out of the base side of the second clamp actuator  154  into the second base-side hydraulic line  186 . Pressure rises in the base-side hydraulic lines  184 ,  186 , which is measured by the base-side pressure sensors  168 ,  170 . Hydraulic fluid passes through the flow divider  176 , through the main base-side hydraulic line  150 , through the base-side control valve  160 , through the first clamp hydraulic line  144 , through the directional control valve  128 , through the truck hydraulic return line  126  and into the hydraulic fluid reservoir  138 . The controller  120  monitors pressures from the pressure sensors  132 ,  168 ,  170  and calculates a base-side to rod-side differential pressure. Initially, the rod-side pressure and the differential pressure rise, then the base-side pressure. The pressures then stabilize when clamp arms  204 ,  205  have reached the full speed that the system  100  is capable of supporting ( FIG.  5   , time  300 ) until the clamp arms  204 ,  205  contact the load  50  ( FIG.  5   , line  301 ). As movement of the clamp arms  204 ,  205  slows down and they begin to compress the load  50 , the rod-side and differential pressures begin to rapidly rise, while the base-side pressures drops. When the controller  120  determines the clamp arms  204 ,  205  have contacted the load  50 , it takes action to end the closing phase of operation and put the smart clamp system  100  in an equalization phase of operation. (See  FIG.  5   , line  302 ). 
     In the first representative embodiment smart clamp system  100 , the controller  120  determines that contact has been made when the differential pressure is increasing faster than a predetermined threshold. In other embodiments, contact may be determined in other ways, such as differential pressure exceeding a preset threshold or using some other type of sensor. In some embodiments, one or more contact sensors on the clamp arms  204 ,  205  may be used, such as limit switches set in the faces of the clamp arms  204 ,  205  that close when they contact the load  50  or conductive contacts that detect contact with the load  50  when resistance between them changes. In some embodiments, one or more flow sensors placed in the main rod-side hydraulic line  148  and/or the base-side hydraulic lines  150 ,  184  ,  186  can be used to detect contact based on when flow decreases in one or more of the lines faster than a predetermined value and/or decreases below a predetermined value. 
       FIG.  4 C  shows a schematic of a first representative embodiment smart clamp system  100  in an equalization phase of operation (time  302  to time  303  in  FIG.  5   ). To put the smart clamp system  100  in the regenerative phase, the controller  120  sends signals to put the base-side control valve  160  in its second position (check valve) and the regeneration valve  164  in its second position (unblocked). The base-side blocking valve  162  remains in its first position (flow blocked). Hydraulic fluid quickly flows from the rod-side of the clamp actuators  152 ,  154 , through the main rod-side hydraulic line  148 , through the regeneration valve  164 , through the main base-side hydraulic line  150 . The hydraulic fluid is blocked by the check valve of the base-side control valve  160  and by the base-side blocking valve  162 , so it flows though the flow divider  176  and into the base-side hydraulic lines  184 ,  186  and into the base-side of the clamp actuators  152 ,  154 . The pressure in the base-side rises, dropping the differential pressure and causing the force applied to the load  50  to ease. If kept in equalization phase/configuration long enough the rod-side pressure will reach the maximum system pressure allowed by the relief valve  108 . Due to the smaller surface area on the rod-side of the actuator pistons  142  compared to the base-side, if the differential pressure were to equalize, the clamp arms  204 ,  205  would start to move away from the load  50 . However, before that happens, the controller  120  ends the equalization phase of operations, triggered by differential pressure dropping below a predetermined threshold. Alternatively, the end of the equalization phase can be triggered by the rod-side pressure sensor  132  reaching a threshold at or almost at the maximum system pressure allowed by the relief valve  108  ( FIG.  5   , line  303 ). 
       FIG.  4 D  shows a schematic of a first representative embodiment smart clamp system  100  at the end of the equalization phase of operation (at time  303  in  FIG.  5   ). The regeneration valve  164  has changed back to the first position, blocking flow from the main rod-side hydraulic line  148  to the main base-side hydraulic line  150 . The hydraulic pump  106  and relief valve  108  maintain pressure in the rod-side at the maximum level. Pressure remains stable in the base-side at a level slightly less than the rod-side, the differential pressure between the rod-side and base-side balancing off the difference between the areas of the base-sides of the actuator pistons  142  and their rod-sides so the forces applied on them are in balance and the clamp arms  204 ,  205  do not move. Since pressure in both the rod-side and the base-side are nearly at the maximum level, the hydraulic fluid is highly compressed and the hydraulic lines are expanded by pressure, which provide the reserve of energy to apply increasing force in the following phases of operation. 
       FIG.  4 E  shows a schematic of a first representative embodiment smart clamp system  100  in a force adjustment phase of operation (time  303  to time  304  in  FIG.  5   ). The controller  120  sends a signal to change the base-side blocking valve  162  to its second (unblocked) position. Hydraulic fluid bleeds out from the base-side hydraulic lines  150 ,  184 ,  186 . Pressure drops on the base-side while remaining higher on the rod-side, increasing differential pressure and increasing the force applied by the clamp arms  204 ,  205  and further compressing the load  50 . The controller  120  calculates the force applied based on the pressure measurements and when the force applied by the clamp arms  204 ,  205  reaches one of the target levels programmed into the controller  120 , then the controller  120  changes the base-side blocking valve  162  to its first (blocked) position ( FIG.  5   , time  304 ). If the force applied overshoots the target level, the regeneration valve  164  can be put in its second position (unblocked) to reduce differential pressure (and force applied). In some embodiments, the controller  120  is configured to modulate the base-side blocking valve  162  based on how close the force applied is to the target force level so that the target force level can be achieved with more accuracy. In this first force adjustment phase of operation, shown from time  303  to time  304  in  FIG.  5   , only a small adjustment is made in the force applied so there is little transient response. 
       FIG.  4 F  shows a schematic of a first representative embodiment smart clamp system  100  in a clamped phase of operation (e.g. time  304  to time  305  in  FIG.  5   ). Once the clamp arms  204 ,  205  have clamped on to the load  50  and are applying a force equal to one of the target levels, the controller  120  sends a signal to the control console  174  indicating to the operator that a first target level of force has been applied. The operator then releases the directional control valve  128  back to the neutral, fully blocked position. Hydraulic fluid slowly leaks past the base-side blocking valve  162  and the base-side control valve  160 , slowly dropping base-side pressure, increasing differential pressure and force applied from time  304  to time  305 . 
     If the lift truck operator wants to increase the force applied to a second target level, then the operator can put the directional control valve  128  again into the cross-flow position. If clamp input pressure (as measured by input pressure sensor  130 ) is greater than the base-side pressure (as measured by the base-side pressure sensors  168 ,  170 ), then the controller  120  will repeat another force adjustment phase of operation (time  305  to time  306  in  FIG.  5   ) putting the base-side blocking valve  162  to its second (unblocked) position (time  305 ) until the second target force level has been achieved (time  306 ). The operator then releases the directional control valve  128  back to the neutral position. In this second force adjustment phase of operation, shown from time  305  to time  306  in  FIG.  5   , a larger adjustment is made in the force applied which results in an overdamped transient response. 
     If the lift truck operator wants to increase the force applied to a third target level, then the force adjustment phase of operation can be repeated again (time  307  to time  308  in  FIG.  5   ) and for as many force levels as have been programmed into the controller  120 . In this third force adjustment phase of operation, shown from time  307  to time  308  in  FIG.  5   , an even larger adjustment is made in the force applied which results in an underdamped transient response. 
     Once the desired force level has been applied to the load  50 , the lift truck operator then operates other controls to lift the carriage  14  along with the smart clamp load handler  104  and load  50  and then move the load  50  to a new location. 
     While the load  50  is still in the clamped phase, differential pressure may change over time, possibly due to imperfect seals in components such as the actuator pistons  142 , the base-side blocking valve  162  or the regeneration valve  164 , changing the force applied to the load  50 . If the controller  120  determines the forced applied has increased more than a predetermined threshold, it is configured to put the regeneration valve  164  in its second position (flow unblocked) until it determines the target force level has been restored. If the controller  120  determines the force applied has dropped more than a predetermined threshold, it is configured to put the base-side blocking valve  162  in its second position (flow unblocked) until it determines the target force level has been restored. The first clamp hydraulic line  144  should be empty or nearly empty right after the initial clamping, so a small volume can flow out of the main base-side hydraulic line  150  and into the first clamp hydraulic line  144 . If the first clamp hydraulic line  144  fills up and unblocking the base-side blocking valve  162  fails to restore the applied force to the target level, then the controller  120  can send a signal to the control console  174  to display an indication that differential pressure is low and the operator should put the directional control valve  128  in the cross-flow position until rod-side pressure is restored. 
       FIG.  4 G  shows a schematic of a first representative embodiment smart clamp system  100  in an opening phase of operation (not shown on  FIG.  5    graph). Once the load  50  has been placed in a desired location, the lift truck operator puts the directional control valve  128  into the flow through position. The hydraulic pump  106  applies hydraulic fluid and pressure to the first clamp hydraulic line  144 , opening the main rod-side hydraulic line check valve  172  and allowing hydraulic fluid to drain from the rod-side into the hydraulic fluid reservoir  138 , dropping the pressure on the rod-side. The residual pressure on the base-side begins to move the clamp arms  204 ,  205  apart. Hydraulic fluid flows through the check valve of the base-side control valve  160 , bolstering pressure on the base-side. Once the operator has released the directional control valve  128  and returned it to the fully blocked position, the clamp arms  204 ,  205  stop moving and the rod-side and base-side pressures stabilize. In the first representative embodiment smart clamp system  100 , if the pressure measured by the input pressure sensor  130  is less than the pressure measured by the rod-side pressure sensor  132  and if pressure measured by the base-side pressure sensors  168 ,  170  is higher than the pressure measured by the rod-side pressure sensor  132  for at least a short period of time (e.g. 200 milliseconds) then the controller  120  will put the base-side control valve  160  in the first (unblocked) position, putting the smart clamp system  100  back in the open phase of operation ( FIG.  4 A ) and ready for another closing phase. In other embodiments, other conditions may be used to trigger putting the smart clamp system  100  back in the open phase of operation. 
     Second Representative Embodiment—Structure 
       FIGS.  6 A and  6 B  show a schematic of a second representative embodiment smart clamp system  400 . The second representative embodiment smart clamp system  400  has the same structure and operation as described for the first representative embodiment smart clamp system  100 , except as noted here. Alternative embodiments described for the first representative embodiment smart clamp system  100  may apply to the second representative embodiment smart clamp system  400 . The second representative embodiment smart clamp system  400  omits the regeneration valve  164  and the input pressure sensor  130 . Most of the advantages of the system would remain, but the advantages of regeneration would be lost. There would be no automated reduction of differential pressure (and force applied) such that occurs in the clamped phase of operation (time  304  to time  305  in  FIG.  5   ) of the first representative embodiment smart clamp system  100 . 
     In some alternative embodiments, the base-side blocking valve  162  may be omitted altogether, along with the rod-side pressure sensor  132 . Additionally, the first base-side pressure sensor  168  and second base-side pressure sensor  170  may be replaced with a single base-side pressure sensor coupled to the main base-side hydraulic line  150 . During the closing phase of operation, the base-side control valve  160  starts in its first (flow through) position, but the controller  120  puts the base-side control valve  160  in its second position (check valve) when base-side pressure exceeds a first target pressure level. After the base-side pressure has achieved steady state (within a predetermined range), the base-side control valve  160  is put in its first position (flow through) until base-side pressure drops below a second target pressure level. The process may be repeated for as many target pressure levels as are set in the programming/logic of the controller  120 . The operator in the lift truck  10  is notified of the current base-side pressure level via the control console  174  or other type of instrumentation. The operator moves the directional control valve  128  to the neutral (fully blocked) position when satisfied with the level of pressure/force applied to the load  50 . 
     Second Representative Embodiment—Method of Operation 
       FIG.  6 C  shows a graph over time of the forces generated by the second representative embodiment smart clamp system  400  during clamping operations. The lines traced out are defined the same as they are in  FIG.  5    for the first representative embodiment smart clamp system  100 , except there is no input force equivalent line  328  since the input pressure sensor  130  is omitted. The fully open phase of operation (time 0 and before in  FIGS.  5  and  6 C ) is the same in the second representative embodiment smart clamp system  400  as in the first representative embodiment smart clamp system  100 . The closing phase of operation (time 0 to time  300  to time  302  in  FIGS.  5  and  6 C ) is the same as well. 
     However, the second representative embodiment smart clamp system  400  does not have an equalization phase of operation (time  302  to time  303  in  FIG.  5   ) followed by a force adjustment phase of operation (time  303  to time  304  in  FIG.  5   ) as does the first representative embodiment smart clamp system  100 . Instead, the second representative embodiment smart clamp system  400  enters an equalization phase of operation (time  302  to time  403  in  FIG.  6 C ) followed by a slow adjustment phase of operation (time  403  to time  404  in  FIG.  6 C ). 
       FIG.  6 A  shows a schematic of a second representative embodiment smart clamp system  400  in an equalization phase of operation (time  302  to time  403  in  FIG.  6 C ). To put the second representative embodiment smart clamp system  400  in the equalization phase, the controller  120  sends signals to put the base-side control valve  160  in its second position (check valve). The base-side blocking valve  162  remains in its first position (flow blocked). The hydraulic fluid in the base-side of the clamp actuators  152 ,  154  can no longer flow out to the hydraulic fluid reservoir  138  as it is blocked by the check valve of the base-side control valve  160  and by the base-side blocking valve  162 . The pressure in the rod-side rises and pressure in the base-side rises almost as much. The differential pressure increases slightly, causing the force applied to the load  50  to increase slightly. If kept in equalization phase/configuration long enough the differential pressure will stabilize at a level slightly larger than when the base-side control valve  160  closed to its flow blocking check valve position. The controller  120  ends the equalization phase of operations triggered by the rod-side pressure sensor  132  reaching a threshold that may be at or almost at the maximum system pressure allowed by the relief valve  108 . 
       FIG.  6 B  shows a schematic of a second representative embodiment smart clamp system  400  in a slow adjustment phase of operation (time  403  to time  404  in  FIG.  6 C ). The controller  120  sends a signal to change the base-side blocking valve  162  to its second (unblocked) position. Hydraulic fluid bleeds out from the base-side hydraulic lines  150 ,  184 ,  186 . Pressure drops on the base-side while remaining higher on the rod-side, increasing differential pressure and increasing the force applied by the clamp arms  204 ,  205  and further compressing the load  50 . The controller  120  calculates the force applied based on the pressure measurements and when the force applied by the clamp arms  204 ,  205  reaches one of the target levels programmed into the controller  120 , the controller  120  sends an indication to the operator that the particular target level has been reached, typically via the control console  174 . The slow adjustment phase continues until the operator returns the directional control valve  128  to the closed position. If the lift truck operator wants to increase the force applied, then the operator can put the directional control valve  128  again into the cross-flow position. Once the desired force level has been applied to the load  50 , the lift truck operator then operates other controls to lift the carriage  14  along with the smart clamp load handler  104  and load  50  and then move the load  50  to a new location. 
     The opening phase of operation is the same in the second representative embodiment smart clamp system  400  as in the first representative embodiment smart clamp system  100 . 
     Third Representative Embodiment 
       FIG.  7    shows a schematic of a third representative embodiment smart clamp system  500  in a force adjustment phase of operation. The third representative embodiment smart clamp system  500  has the same structure and operation as described for the first representative embodiment smart clamp system  100 , excepted as noted here. Alternative embodiments described for the first representative embodiment smart clamp system  100  may apply to the third representative embodiment smart clamp system  500 . The third representative embodiment smart clamp system  500  omits the flow divider  176 , and the base equalization valves  134 ,  136 . This is a less expensive embodiment, but some ability to maintain even movement of the clamp arms  204 ,  205  is lost. The rod-side pressure sensor  132  and the base-side pressure sensors  168 ,  170  are replaced with a differential pressure sensor  502  coupled between the main rod-side hydraulic line  148  and the main base-side hydraulic line  150 . The input pressure sensor  130  is omitted. This is less expensive, but the controller  120  must rely entirely on the differential pressure for making decisions rather than also using the input pressure, the rod-side pressure and the base-side pressure, which results in some loss of precision and consistency in performance. 
     In the opening phase of operation, the condition for putting the base-side control valve  160  in the first (unblocked) position is different. In the third representative embodiment smart clamp system  500 , if the differential pressure measured by the differential pressure sensor  502  is negative (base side larger than rod side) for at least a short period of time (e.g. 200 milliseconds) then the controller  120  will put the base-side control valve  160  in the first (unblocked) position, putting the third representative embodiment smart clamp system  500  back in the open phase of operation and ready for another closing phase. 
     The third representative embodiment smart clamp system  500  loses the ability to advance from one target force level to another in the clamped phase of operations by moving the directional control valve  128  from the neutral to the cross-flow position as there is no way to determine if input pressure is greater than base-side pressure. Instead, the operator uses the control console  174  to command the third representative embodiment smart clamp system  500  to advance to another target force level. In other embodiments, other suitable mechanisms can be used to advance to another target force level. 
     In some alternative embodiments, the differential pressure sensor  502  can be replaced with one or more pressure switches. Each pressure switch would trigger repositioning of one or more of the valves  160 ,  162 ,  164  to a particular state, either directly or via controller  120  logic/programming. 
     Fourth Representative Embodiment 
       FIG.  8    shows a schematic of a fourth representative embodiment smart clamp system  600  in an equalization phase of operation. The fourth representative embodiment smart clamp system  600  has the same structure and operation as described for the first representative embodiment smart clamp system  100 , excepted as noted here. Alternative embodiments described for the first representative embodiment smart clamp system  100  may apply to the fourth representative embodiment smart clamp system  600 . The fourth representative embodiment smart clamp system  600  omits the base-side control valve  160  and the base-side blocking valve  162 . This is a less expensive embodiment, but gives up most of the precision and accuracy of the first representative embodiment smart clamp system  100 . After contact detection (rising differential pressure, dropping base-side pressure), the regeneration valve  164  can be opened and modulated to achieve the target level force applied. If the force applied is too low, the regeneration valve  164  can be modulated to close more, allowing less flow and pressure to the base-side. If the force applied is to high, the regeneration valve  164  can be modulated to open more, allowing more flow and pressure to the base-side. The fourth representative embodiment smart clamp system  600  would not charge to the maximum pressure allowed by the relief valve  108 , but instead would dynamically adjust the regeneration valve  164  constantly keeping the force applied to the load  50  at target level until the directional control valve  128  is put back in the neutral (flow blocked) position. 
     Similar to the third representative embodiment smart clamp system  500 , the fourth representative embodiment smart clamp system  600  loses the ability to advance from one target force level to another in the clamped phase of operations by moving the directional control valve  128  from the neutral to the cross-flow position as there is no way to determine if input pressure is greater than base-side pressure. Instead, the operator uses the control console  174  to command the fourth representative embodiment smart clamp system  600  to advance to another target force level. In other embodiments, other suitable mechanisms can be used to advance to another target force level. 
     Fifth Representative Embodiment—Structure 
       FIGS.  9 A,  9 B, and  9 C  show a schematic of a fifth representative embodiment smart clamp system  700 . The fifth representative embodiment smart clamp system  700  has the same structure and operation as described for the first representative embodiment smart clamp system  100 , excepted as noted here. Alternative embodiments described for the first representative embodiment smart clamp system  100  may apply to the fifth representative embodiment smart clamp system  700 . The fifth representative embodiment smart clamp system  700  omits the input pressure sensor  130 , the regeneration valve  164 , the base-side control valve  160  and the base-side blocking valve  162 . Instead, the fifth representative embodiment smart clamp system  700  has a rod-side control valve  760  and a rod-side blocking valve  762  configured in parallel in line with the main rod-side hydraulic line  148  between the second clamp hydraulic line  146  and the main rod-side hydraulic line check valve  172 . The rod-side control valve  760  and the rod-side blocking valve  762  are structurally similar to the base-side control valve  160  and the base-side blocking valve  162  respectively and have similar operational characteristics. The alternatives and options mentioned for the base-side control valve  160  and the base-side blocking valve  162  may be used with the rod-side control valve  760  and rod-side blocking valve  762  as well. 
     In some alternative embodiments, the rod-side blocking valve  762  may be replaced with a fixed orifice. This will reduce cost and complexity. Since the rod-side blocking valve  762  is upstream (towards the hydraulic pump  106 ) from the main rod-side hydraulic line check valve  172 , it is not needed to block flow out of the rod-side to maintain the base end pressure after hydraulic pressure from the hydraulic pump  106  is removed (typically by putting the directional control valve  128  in its fully block or straight flow positions) as the main rod-side hydraulic line check valve  172  will do that. 
     In some alternative embodiments, the rod-side blocking valve  762  may be omitted altogether, along with the first base-side pressure sensor  168  and the second base-side pressure sensor  170 . During the closing phase of operation, the controller  120  puts the rod-side control valve  760  in its second position (check valve) when rod-side pressure (measured by rod-side pressure sensor  132 ) exceeds a first target pressure level. After the rod-side pressure has achieved steady state (within a predetermined range), the rod-side control valve  760  is put in its first position (flow through) until rod-side pressure exceeds a second target pressure level. After the rod-side pressure has achieved steady state (within a predetermined range), the rod-side control valve  760  is put in its first position (flow through) until rod-side pressure exceeds a third target pressure level. The process may be repeated for as many target pressure levels as are set in the programming/logic of the controller  120 . The operator in the lift truck  10  is notified of the current rod-side pressure level or force applied to the load  50  (derived from the rod-side pressure) via the control console  174  or other type of instrumentation. The operator moves the directional control valve  128  to the neutral (fully blocked) position when satisfied with the level of pressure/force applied to the load  50 . Anytime the controller  120  detects that rod-side pressure has dropped below a low pressure threshold, then the rod-side control valve  760  is put in the first position (flow through) as this indicates that the clamp arms  204 ,  205  are not in contact with the load  50 . 
     Fifth Representative Embodiment—Method of Operation 
       FIG.  9 D  shows a graph over time of the forces generated by the fifth representative embodiment smart clamp system  700  during clamping operations. The lines traced out are defined the same as they are in  FIG.  5    for the first representative embodiment smart clamp system  100 , except there is no input force equivalent line  328  since the input pressure sensor  130  is omitted. 
     When the fifth representative embodiment smart clamp system  700  is in a fully open phase of operation (before time 0 in  FIG.  9 D ), the clamp arms  204 ,  205  are fully open and not in contact with the load  50 . The directional control valve  128  is in a closed position with all four ports blocked. The rod-side control valve  760  is its first position (flow unblocked), rod-side blocking valve  762  is in its first position (flow blocked). 
       FIG.  9 A  shows a schematic of the fifth representative embodiment smart clamp system  700  in a closing phase of operation (time 0 to time  302  in  FIG.  9 D ). The closing phase of operation is commenced with the directional control valve  128  being put (usually by a human operator, but in some embodiments, by an electrical controller or other automated controller) in its cross-over position. Pressurized hydraulic fluid from the truck hydraulic feed line  124  flows into the second clamp hydraulic line  146 , through the main rod-side hydraulic line  148 , through the rod-side control valve  760 , through the main rod-side hydraulic line check valve  172 , through the first rod-side hydraulic line  180  and second rod-side hydraulic line  182  into the rod side of the first clamp actuator  152  and second clamp actuator  154 . Hydraulic pressure builds in the rod side of the clamp actuators  152 ,  154 , measured by the rod-side pressure sensor  132 , until enough force is generated to overcome friction and the actuator pistons  142  move inward, moving the clamp arms  204 ,  205  towards each other and toward the load  50  ( FIG.  9 D , time 0). Hydraulic fluid is forced out of the base side of the first clamp actuator  152  into the first base-side hydraulic line  184  and out of the base side of the second clamp actuator  154  into the second base-side hydraulic line  186 . Pressure rises in the base-side hydraulic lines  184 ,  186 , which is measured by the base-side pressure sensors  168 ,  170 . Hydraulic fluid passes through the flow divider  176 , through the main base-side hydraulic line  150 , through the first clamp hydraulic line  144 , through the directional control valve  128 , through the truck hydraulic return line  126  and into the hydraulic fluid reservoir  138 . The controller  120  monitors pressures from the pressure sensors  132 ,  168 ,  170  and calculates a base-side to rod-side differential pressure. As the clamp arms  204 ,  205  first start to move, rod-side and differential pressures rise, then the base-side pressures. The pressures then stabilize when clamp arms  204 ,  205  have reached the full speed that the system  100  is capable of supporting ( FIG.  9 D , time  300 ) until the clamp arms  204 ,  205  contact the load  50 . ( FIG.  9 D , line  301 ). As movement of the clamp arms  204 ,  205  slows down and they begin to compress the load  50 , the rod-side pressure rises, while the base-side pressures drops, causing the differential pressure to rapidly increase. When the controller  120  determines the clamp arms  204 ,  205  have contacted the load  50 , it takes action to end the closing phase of operation and put the smart clamp system  100  in an equalization phase of operation (time  302  to time  403  in  FIG.  9 D ). 
       FIG.  9 B  shows a schematic of a fifth representative embodiment smart clamp system  700  in an equalization phase of operation (time  302  to time  403  in  FIG.  9 D ). To put the fifth representative embodiment smart clamp system  700  in the equalization phase, the controller  120  sends signals to put the rod-side control valve  760  in its second position (check valve). The rod-side blocking valve  762  remains in its first position (flow blocked). The pressure in the rod-side then drops rapidly since it is cut off from the hydraulic pump  106 . The hydraulic fluid in the base-side of the clamp actuators  152 ,  154  continues to flow out through the flow divider  176  to the hydraulic fluid reservoir  138  causing the pressure in the base-side to drop rapidly as well, largely matching the drop in rod-side pressure, so the differential pressure and the force applied to the load remains substantially the same. The controller  120  ends the equalization phase of operations, triggered by rod-side and/or base-side pressure dropping below a predetermined threshold, transitioning to a slow adjustment phase of operation. 
       FIG.  9 C  shows a schematic of a fifth representative embodiment smart clamp system  700  in the slow adjustment phase of operation (time  403  to time  404  in  FIG.  9 D ). The controller  120  sends a signal to change the rod-side blocking valve  762  to its second (unblocked) position. The rod-side blocking valve  762  has a smaller passage in its unblocked position than the rod-side control valve  760 , so pressure increases gradually on the rod-side. Hydraulic fluid bleeds out from the base-side hydraulic lines  150 ,  184 ,  186 . Only a small amount of pressure remains on the base-side, just the amount of pressure needed to push the hydraulic fluid displaced from the base-side of the clamp actuators  152 ,  154  through the flow divider  176  and the base-side hydraulic lines  184 ,  186 ,  150 . The controller  120  calculates the force applied based on the pressure measurements and when the force applied by the clamp arms  204 ,  205  reaches one of the target levels programmed into the controller  120 , then the controller  120  sends an indication to the operator that the particular target level has been reached, typically via the control console  174 . The slow adjustment phase continues until the operator returns the directional control valve  128  to the closed position. If the lift truck operator wants to increase the force applied, then the operator can put the directional control valve  128  again into the cross-flow position. Once the desired force level has been applied to the load  50 , the lift truck operator then operates other controls to lift the carriage  14  along with the smart clamp load handler  104  and load  50  and then move the load  50  to a new location.