Patent Publication Number: US-5297019-A

Title: Control and hydraulic system for liftcrane

Description:
REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. Ser. No. 07/418,879, filed on Oct. 10, 1989 U.S. Pat. No. 5,189,605. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to liftcranes and more particularly to an improved control and hydraulic system for a liftcrane. 
     A liftcrane is a type of heavy construction equipment characterized by an upward extending boom from which loads can be carried or otherwise handled by retractable cables. Liftcranes are available in different sizes. The size of a liftcrane is associated with the weight (maximum) that the liftcrane is able to lift. This size is expressed in tons, e.g. 50 tons. 
     The boom is attached to the upper works of the liftcrane. The upper works are usually rotatable upon the lower works of the liftcrane. If the liftcrane is mobile, the lower works may include a pair of crawlers (also referred to as tracks). The boom is raised or lowered by means of a cable and the upper works also include a drum upon which the boom cable can be wound. Another drum (referred to as a hoist drum) is provided for cabling used to raise and lower a load from the boom. A second hoist drum (also referred to as the whip hoist drum) is usually included rearward from the first hoist drum. The whip hoist is used independently or in association with the first hoist. Different types of attachments for the cabling are used for lifting, clamshell, dragline and so on. Each of these combinations of drums, cables and attachments, such as the boom or clam shell are considered herein to be mechanical subsystems of the liftcrane. Additional mechanical subsystems may be included for operation of a gantry, the tracks, counterweights, stabilization, counterbalancing and swing (rotation of the upper works with respect to the lower works). Mechanical subsystems in addition to these may also be provided. 
     As part of the upper works, a cab is provided from which an operator can control the liftcrane. Numerous controls such as levers, handles, knobs, and switches are provided in the operator&#39;s cab by which the various mechanical subsystems of the liftcrane can be controlled. Use of a liftcrane requires a high level of skill and concentration on the part of the operator who must be able to simultaneously manipulate and coordinate the various mechanical systems to perform routine operations. 
     The two most common types of power systems for liftcranes are friction-clutch and hydraulic. In the former type, the various mechanical subsystems of the liftcrane connect by means of clutches that frictionally engage a drive shaft driven by the liftcrane engine. The friction-clutch liftcrane design is considered generally older than the hydraulic type of liftcrane design. 
     In hydraulic systems, an engine powers a hydraulic pump that in turn drives an actuator (such as a motor or cylinder) associated with each of the specific mechanical subsystems. The actuators translate hydraulic pressure forces to mechanical forces thereby imparting movement to the mechanical subsystems of the liftcrane. 
     Hydraulic systems used on construction machinery may be divided into two types--open loop and closed loop. Up until now, most hydraulic liftcranes use primarily an open loop hydraulic system. In an open loop system, hydraulic fluid is pumped (under high pressure provided by a pump) to the actuator. After the hydraulic fluid is used in the actuator, it flows back (under low pressure) to a reservoir before it is recycled by the pump. The loop is considered &#34;open&#34; because the reservoir intervenes on the fluid return path from the actuator before it is recycled by the pump. Open loops systems control actuator speed by means of valves. Typically, the operator adjusts a valve to a setting to allow a portion of flow to the actuator, thereby controlling the actuator speed. The valve can be adjusted to supply flow to either side of the actuator thereby reversing actuator direction. 
     By contrast, in a closed loop system, return flow from an actuator goes directly back to the pump; i.e., the loop is considered &#34;closed&#34;. Closed loop systems control speed and direction by changing the pump output. 
     Up until now, open loop systems have been generally favored over closed loop systems because of several factors. In an open loop system, a single pump can be made to power relatively independent, multiple mechanical subsystems by using valves to meter the available pump flow to the actuators. Also, cylinders, and other devices which store fluid, are easily operated since the pump does not rely directly on return flow for source fluid. Because a single pump usually operates several mechanical subsystems, it is easy to bring a large percentage of the liftcrane&#39;s pumping capability to bear on a single mechanical subsystem. Auxiliary mechanical subsystems can be easily added to the system. 
     However, open loop systems have serious shortcomings compared to closed loop systems, the most significant of which is lack of efficiency. A liftcrane is often required to operate with one mechanical subsystem fully loaded and another mechanical subsystem unloaded yet with both turning at full speed, e.g. in operations such as clamshell, grapple, level-luffing. An open loop system having a single pump must maintain pressure sufficient to drive the fully loaded mechanical subsystem. Consequently, flow to the unloaded mechanical subsystems wastes an amount of energy equal to the unloaded flow multiplied by the unrequired pressure. 
     Open loop systems also waste energy across the valves needed for acceptable operation. For example, the main control valves in a typical load sensing, open loop system (the most efficient type of open loop system for a liftcrane) dissipates energy equal to 300-400 PSI times the load flow. Counterbalance valves required for load holding typically waste energy equal to 500-2,000 PSI times the load flow. 
     As a result of the differences in efficiency noted above, a single pump open loop system requires considerably more horsepower to do the same work as a closed loop system. This additional horsepower could easily consume thousands of gallons of fuel annually. Moreover, all this wasted energy converts to heat. It is no surprise, therefore, that open loop systems require larger oil coolers than comparable closed loop systems. 
     Controllability can be another problem for open loop circuits. Since all the main control valves are presented with the same system pressure, the functions they control are subject to some degree of load interference, i.e., changes in pressure may cause unintended changes in actuator speed. Generally, open loop control valves are pressure compensated to minimize load interference. But none of these devices are perfect and speed changes of 25% with swings in system pressure are not atypical. This degree of speed change is disruptive to liftcrane operation and potentially dangerous. 
     To avoid having to use an extremely large pump, many open loop systems have devices which limit flow demand when multiple mechanical subsystems are engaged. Such devices, along with the required load sensing circuits and counterbalance valves mentioned above, are prone to instability. It can be very difficult to adjust these devices to work properly under all the varied operating conditions of a liftcrane. 
     An approach taken by some liftcranes manufacturers with open loop systems to minimize the aforementioned problems is to use multi-pump open loop systems. This approach surrenders the main advantage that the open loop has over closed loop, i.e. the ability to power many functions with a single pump. 
     In summary, although presently available liftcranes generally use open loop hydraulic systems, these are very inefficient and this inefficiency costs the manufacturers by requiring large engines and oil coolers and it costs the user in the form of high fuel bills. Moreover, another disadvantage is that open loop systems in general can have poor controllability under some operating conditions. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved control system for a liftcrane. The liftcrane has mechanical subsystems powered by a engine-driven closed loop hydraulic system. The liftcrane also includes controls for outputting signals for operation of the mechanical subsystems and a programmable controller connected and responsive to the controls and connected to the mechanical subsystems. The programmable controller is capable of running a routine for controlling the mechanical subsystems. A first set of sensors is operable to sense the pressure in the closed loop hydraulic system at each of the mechanical subsystems in a first set of mechanical subsystems and provide an output to the programmable controller indicative of the hydraulic pressure sensed at each of these mechanical subsystems. A second set of sensors is operable to sense the position or speed of each of the mechanical subsystems in a second set of mechanical subsystems and provide an output to the programmable controller indicative of the position or speed sensed at each of the mechanical subsystems of the second set of mechanical subsystems. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a flow chart depicting the control system of an embodiment of the present invention. 
     FIG. 2 is a flow chart of a liftcrane operating routine capable of running on the control system depicted in the embodiment in FIG. 1. 
     FIG. 3 is a diagram of a closed loop hydraulic system of an embodiment of the present invention. 
     FIG. 4 is a schematic diagram of a control system for a second preferred embodiment of the present invention. 
     FIG. 5 is a schematic of a portion of the second preferred embodiment of the liftcrane control and hydraulic system relating to swing operation. 
     FIG. 6 is a schematic of a portion of the second preferred embodiment of the liftcrane control and hydraulic system relating to hoist operation. 
     FIG. 7 is a flow chart of the routine that may be run on the programmable controller of the second preferred embodiment of the present invention of FIG. 4. 
    
    
     DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS 
     FIG. 1 depicts a flow chart of an embodiment of an improved control system for a liftcrane. The various mechanical subsystems 10 of the liftcrane include pumps and actuators for the front hoist, rear hoist (whip), swing, boom, and left and right crawlers. In addition, there are subsystems for such things as counterweight handling, crawler extension, gantry raising, fan motors, warnings lights, visual display and so on. (As used herein, mechanical subsystems include those which may be characterized strictly as mechanical, e.g. booms, as well as others subsystems such as electrical gauges and video, but not limited to these). The mechanical subsystems 10 are under the control of an operator who occupies a position in the cab in the upper works of the liftcrane. In the cab are various operator controls 12 used for operation and control of the mechanical systems of the liftcrane. These operator controls 12 can be of various types such as switches, shifting levers etc., but can readily be divided into switch-type controls 14 (digital, ON/OFF) and variable controls 15 (analog or infinite position). The switch-type controls 14 are used for on/off type activities, such as setting a brake, whereas the variable controls 15 are used for activities such as positioning the boom, hoists, or swing. In addition, the operator controls 12 include a mode selector 18 whose function is to tailor the operation of the liftcrane for specific type of activities, as explained below. (For purposes of the control system of this embodiment, the mode selector 18 is considered to be a digital device even though there may be more than two modes available). In the present embodiment, the mode selection switch 18 includes selections for main hydraulic mode, counterweight handling mode, crawler extension mode, high speed mode, clamshell mode and free-fall mode. Some of these modes are exclusive of others (such as main hydraulic and free-fall) where their functions are clearly incompatible; otherwise these modes may be combined. 
     The outputs of the operator controls 12 are directed to a controller 20 and specifically to an interface 22 of the controller 20. The interface 22 receives signals 24 from each of the variable controls 15 and signals 26 and 27 from each of the switch-type controls 14 and the mode selector 18, respectively. The interface 22 in turn is connected to a CPU (central processing unit) 28. The interface 22 handles the signals 24, 26, and 27 in a similar manner. The controller 20 may be a unit such as the model IHC (Intelligent Hydraulic Controller) manufactured by Hydro Electronic Devices Corporation. The CPU 28 may be an Intel 8052. The controller 20 should be designed for heavy duty service under the conditions associated with outdoor construction activity. 
     The CPU 28 runs a routine which recognizes and interprets the commands from the operator (via the operator control 12) and outputs information back through the interface 22 directing the mechanical subsystems 10 to function in accordance with the operator&#39;s instructions. Movements, positions and other information about the mechanical subsystems 10 are monitored by sensors 30 which include both analog sensors 32 and switch-type sensors 34. Information from the sensors 30 is fed back to the interface 22 and in turn to the CPU 28. This information about the mechanical subsystems 10 provided by the sensors 30 is used by the routine running on the CPU 28 to determine if the liftcrane is operating properly. 
     The present invention provides significant advantages through the use of the controller 20. As mentioned above, high levels of skill and concentration are required of liftcrane operators to coordinate various liftcrane controls to perform even routine operations. Also, some liftcrane operations have to be performed very slowly to ensure safety. These operations can be very fatiguing and tedious. Through the use of the routine provided by the control system and running on the CPU 28, various complicated maneuvers can be simplified or improved. 
     One example of how the present invention can improve liftcrane operation is mode selection. Mode selection refers to tailoring the operation of the liftcrane for the particular task being performed. The mode selector 18 is set by the operator to change the way that the crane operates. The change in mode is carried out by the routine on CPU 28. With the change in mode, various of the operator controls 12 in the cab function in distinctly different ways and even control different mechanical subsystems in order that the controls are specifically suited to the task to be accomplished. With the change of mode, the routine can establish certain functional relationships between several separate mechanical subsystems for particular liftcrane activities (such as dragline or clamshell operations). Previously, such operations required sometimes difficult simultaneous coordination of several different controls by the operator. 
     Another example of how this embodiment of the invention can improve liftcrane operation is that the variable controls 15 can be set for either fine, precise, small-scale movements or for large-scale movements of the corresponding mechanical subsystems. Thus fewer and simpler controls may be needed in 
     Still another example of how this embodiment of the invention improves liftcrane operation is in ease of maintenance and trouble-shooting. Instead of attempting to monitor each discreet mechanical subsystem, as in previous liftcranes, a mechanic can obtain information on all the mechanical subsystems of the liftcrane by connecting a computer (such as a laptop personal computer) to the controller and downloading the sensor data. Similarly, trouble-shooting could be accomplished by inputting specific control data directly to the controller, measuring the resultant sensor data, and comparing this to the expected sensor data. 
     Referring to FIG. 2, there is depicted a flow chart of the liftcrane operating routine 48 of an embodiment the present invention. This routine is stored in the controller and may be stored in CPU 28. In this embodiment, the routine 48 is stored in EPROM, although other media for storage may be used. The source code for this routine in this first embodiment is set out in Appendix I. This routine set forth in Appendix I is specifically tailored for liftcrane standards in the Netherlands and includes provisions specifically directed to the safety standards there. However, the routine may also be used in the United States and in other countries or could easily be modified following the principles set out herein. 
     The liftcrane operating routine 48 is intended to run continuously on the CPU 28 (in FIG. 1) in a loop fashion. The liftcrane operating routine 48 on the CPU reads information provided from the interface 22 (in FIG. 1) which appears as data accessible to the routine at certain addresses. Output commands from the liftcrane operating routine 48 are transmitted from the CPU 28 to the interface 22 and there are converted to signals in the form required to operate the various mechanical subsystems. 
     In this embodiment of the liftcrane control system, when the liftcrane is initially turned on (or if the routine reboots itself or restores itself due to a transient fault), the liftcrane operating routine 48 includes an initialization subroutine 50 that initializes variables and reads certain parameters. Following this, an operating mode subroutine 52 reads data indicating which operating mode has been selected by the operator for the liftcrane. Next, a charge pressure reset/out of range subroutine 54 checks to determine if the hydraulic pressure in the liftcrane is in a proper operating range. Following this is a director subroutine 56 which is the main subroutine for the operation of the crane. From the director subroutine 56 the program branches into one of five subroutines associated with operation of the major mechanical subsystems. These subroutines control the function of the major mechanical subsystems with which they are associated: front hoist drum subroutine 58, rear hoist drum subroutine 60, boom hoist drum subroutine 62, right track subroutine 64, and left track subroutine 66. After these subroutines finish, the liftcrane operating routine 48 returns to the operating mode subroutine 52 and the starts all over again. As the routine cycles, changes made by the operator at the controls will be read by the liftcrane operating routine and changes in the operation of mechanical systems will follow. In addition, there are subroutines for swing supply and track supply that are run from the charge pressure reset/out-of-range subroutine 54. In the event that the pressure is not in the proper operating range, brakes will be applied to the swing and track to insure safety. A counterweight handling subroutine 74 branches from the director subroutine 56. A swing subroutine 76 also branches from the director subroutine 54. The swing subroutine 76 is called during each cycle of the director subroutine 54 to enhance a smooth movement of the swing. 
     A watchdog chip may be provided in controller 20 so that in the event of a failure of the operating routine, the CPU will reboot itself and start the initialization process 50 again. 
     To provide additional modes of operation or to alter the response of any of the components of the mechanical subsystems 10, the liftcrane operating routine 48 can be augmented or modified. For example, additional subroutines can be provided for new operating modes. One example is a level-luffing operating mode. Level-luffing refers to horizontal movement of a load. This involves both movement of the boom and simultaneous movement of the load hoist. This procedure requires a high degree of skill on the part of the operator and it is often performed when moving loads across horizontal surfaces such as floors. Movement of loads horizontally is often required in liftcrane operation, but can be very difficult to do where it may be required to move the load out of sight of the liftcrane operator. Through appropriate programming and computation of trigonometric functions in the liftcrane operating routine, load level-luffing can be precisely and easily provided. 
     Still another example of a type of a subroutine that can be provided by the control system of the present invention is operation playback. With the addition of a means for data storage, the controller can provide that once an operator performs a certain operation or activity, regardless of how complicated it is, the operation can be recorded and &#34;learned&#34; by the routine on the CPU 28. Then the same activity can be played back by the operator and performed over and over again, thereby eliminating some of the tedium and difficulty of the operation. 
     In addition, another subroutine that can be added would be an area avoidance subroutine. Where the liftcrane is operating in a location near easily damaged items or hazardous materials such as electric lines or in a chemical plant, the liftcrane operator can provide information via the control panel indicating areas prohibited to the movement of the liftcrane. The liftcrane operating subroutine would then completely prevent any liftcrane movements that might impinge on the prohibited area thereby highly enhancing the safety of the liftcrane operation. This could be accomplished by having the liftcrane operator first move the crane to a boundary in one direction and indicate by the control panel that this is a first boundary, and then move the crane through non-prohibited area to a second boundary and indicate by the control panel that this is a second boundary. These boundary positions would be recorded by sensors and stored as data in the operating routine. Thereafter, during each cycle of the operating routine, the routine would check the crane movement against the boundaries of the prohibited area and refuse to execute any command that would cause the crane to encroach on the prohibited area. 
     Another subroutine can provide for use of a counterbalancing system. Such a counterbalancing system is described in copending U.S. application Ser. No. 07/269,222, entitled &#34;Crane And Lift Enhancing Beam Attachment With Movable Counterweight&#34;, filed Nov. 9, 1988,U.S. Pat. No. 4,953,722 and incorporated herein by reference. 
     Another advantage of the present invention is that the operation and safety features of the liftcrane can easily be adapted for the different requirements of different countries. For example, in the Netherlands an exterior warning light must be provided when the liftcrane is in the free-fall mode. This can readily be provided by the routine by the addition of several lines of code (refer to Appendix I, lines 2000 to 2095). 
     The flexibility of the control system of this embodiment finds particular advantage when used in conjunction with the closed loop hydraulic system of this embodiment of the invention. Most liftcranes use an open loop system which have the inherent disadvantages, as mentioned above. This embodiment uses a closed loop hydraulic system operating under the programmable control system. 
     Referring to FIG. 3, there is represented an engine 80 in this embodiment of the invention. The engine 80 can produce 210 horsepower. The engine size is chosen to be suitable for the size the liftcrane which in this case is rated at 50 tons. For different sizes of liftcranes, different sizes of engines would be used. 
     The engine 80 drives a plurality of main pumps 82. In this embodiment, there are six main pumps, each associated with one of the major mechanical subsystems of the liftcrane. Each of the pumps drives an actuator (motor) associated with its mechanical subsystem. Each of the six actuators is connected to its corresponding pump by a pair of hydraulic lines to form the closed loop. This enables application of hydraulic force to the actuators in either direction. A reservoir 102 is connected to the engine 80 outside of the closed loops between the pumps 82 and the six mechanical subsystems. 
     The actuators in the major mechanical subsystems include the following: A swing motor 104 controls the swing (movement of the upper works in relation to the lower works). A boom hoist motor 105 raises and lowers the boom. A rear hoist motor 106 controls the rear hoist drum and the front hoist motor 107 controls the front hoist drum. A left and right crawler motors 108 and 110 control the tractor crawlers, respectively. Additional mechanical subsystems may be powered either by use of an auxiliary pump, such as a fan pilot pressure pump 130, or by diverting flow from one or more of the main hydraulic pumps. This embodiment uses this former method to power the crawler extenders and gantry. These mechanical subsystems are connected to actuators associated with them by a solenoid valve 134. 
     One of the drawbacks normally associated with the multiple closed loop liftcrane system is the inability to bring a large percentage of the machine&#39;s pumping ability to bear on a single mechanical subsystem where high speed is required. This embodiment overcomes this drawback by means of the diverting valve assembly 150. The diverting valve assembly 150 operates to combine the closed loops of two or more pumps with a single actuator so that the operation of the mechanical subsystem associated with the actuator can take advantage of more than just the single pump normally associated with it. Consequently, the closed loop hydraulic system of the present invention is able to duplicate performance of an open loop system while also providing the advantages of the closed loop system. 
     In the present embodiment, the diverting valve assembly 150 provides the ability to direct a large percentage of the liftcrane&#39;s total pumping capacity to either the main or the whip hoist. The diverting valve assembly 150 also provides the ability to direct a substantial percentage of the liftcrane&#39;s total pumping capability to several of the auxiliary mechanical subsystems. The diverting valve assembly 150 also has the ability to combine several of the pumps to provide charge or pilot flow sufficient to operate large cylinders. 
     The ability to operate the diverting valve assembly 150 in the manner described is facilitated by this embodiment. The operation of the diverting valve assembly 150 to meet or exceed the levels of performance associated with an open loop system is provided by the routine described herein. As a result, the present embodiment can provide a high level of performance combined with economy and efficiency. Moreover, the present embodiment provides new features to augment an operator&#39;s skill and efficiency and also can provide a higher level of safety heretofore unavailable in liftcranes. 
     Referring to FIG. 4, there is depicted a schematic diagram of a control system for a second preferred embodiment of the present invention. In FIG. 4, a set of liftcrane mechanical subsystems 200 may be operated by a set of operator controls 202 located in an operator&#39;s cab 203. The set of operator controls 202 includes analog controls 206, digital controls 208, and mode selection controls 210. The set of operator controls 202 is connected to a programmable controller 212 which includes a CPU 214 capable of running an operating routine for the operation of the liftcrane mechanical systems. As in the previous embodiment, the analog controls 206 and the digital controls 208 (including the mode selection controls 210), respectively, are connected to an interface 218 to transfer information about the desired operation from the set 202 of operator controls to the CPU 214. As in the previous embodiment, sensors 222 associated with the set 200 of mechanical subsystems monitor the status thereof and provide information back to programmable controller 212. The sensors 222 include both analog sensors 224 that connect to the programmable controller 212 via the interface 218 to monitor a set 225 of mechanical subsystems, and limit switches 226 that connect to the programmable controller 212 via the interface 218 to monitor another set 227 of mechanical subsystems. In this embodiment, the analog sensors 224 include both pressure transducers 228 and position-speed sensors 230. The pressure transducers 228 and position-speed sensors 230 may be used to monitor separate sets 231 and 232, respectively, of mechanical subsystems or, for certain mechanical subsystems, the pressure transducers 228 and position-speed sensors 230 may be used in conjunction with a single mechanical subsystem to augment the control and performance thereof. (Thus, as used herein, mechanical subsystems monitored by pressure sensors and position-speed sensors need not necessarily be separate mechanical subsytems). Mechanical subsystems that may utilize both pressure sensors and position-speed sensors include the swing and each of the hoists. 
     The addition of pressure sensors in the second preferred embodiment allows for improved liftcrane operation over the previous embodiment in which only position-speed sensors are used. In particular, the second preferred embodiment provides for improved liftcrane operation by having the capability to combine, either simultaneously or alternately, both pressure control as well as position-speed control in performing certain functions. This is particularly useful for example for any liftcrane function in which two or more lines are used together. This would include functions such as clamshell, pile driving, tagline, magnet and grapple. 
     For example, in performing clamshell work in a prior liftcrane, the operator must support the load with one line and maintain slight tension on the other by the simultaneous control of two or more separate handles and two brake pedals in the cab. Smooth, efficient operation of a clamshell can be relatively difficult requiring a high degree of skill and coordination on the part of the operator. With this second preferred embodiment of the present invention, by using a pressure sensor on the pump connected to the hoist drum, the controller can, when required, command the pump to maintain a fixed, low tension (pressure) hoist on one line and then instantly revert to full power capability for the remainder of the clam operating cycle. Thus, operation is simplified. 
     With respect to the other functions, similar advantages obtain. For each, the simultaneous control of two separate mechanical subsystems in which one is operated in response to a pressure sensed allows for benefits associated with simplification of operation, increased safety, and greater efficiency. For example, with magnet work, a cable is maintained to steady the magnet. The operation of this steadying cable can be managed by the controller to maintain a fixed pressure to steady the magnet. Similarly, in pile driving operations, one of the lines can be put under pressure control while the other is operated to move the pile driver. 
     In the second preferred embodiment of the present invention, improved, smoother swing operation is provided by having pressure sensors that provide output signals to the programmable controller. In this embodiment of the invention, the pump associated with the swing can be operated to maintain a commanded pressure (i.e. &#34;torque output&#34;). This allows a standard displacement pump to be used as a free-coasting swing pump and provides for smoother operation of the swing. In FIG. 5, there is depicted a schematic of one embodiment of a portion of the liftcrane control and hydraulic system for the swing. A control handle 234 is located in the operator&#39;s cab. The control handle 234 includes a lever 236 movable across a range of positions. The control handle 234 is a part of the operator controls and accordingly the control handle 234 provides an output 235 to the programmable controller 212. A swing motor 238 is connected to the upper works and lower works (neither shown) to effect the relative movement therebetween. The swing motor 238 is driven by a pump 240 to which it is connected by first and second hydraulic lines 242 and 244 (i.e. a closed loop 246). Two pressure sensors are associated with the swing motor 238. These pressure sensors are preferably pressure transducers. A first pressure sensor 248 is connected to the first hydraulic line 242 and a second pressure sensor 250 is connected to the second hydraulic line 244. The first and second pressure sensors 248 and 250 are connected to the programmable controller 212 to provide feedback signals 252 and 254 thereto indicative of the pressure on each side of the closed loop 246 connected to the swing motor 238. The routine run on the programmable controller 212 compares these feedback signals with the signal 235 obtained from the control handle 234. The routine on the programmable controller then generates an output 256 to the pump 240 to modify the operation of the pump, if necessary to effect the desired operation of the swing. As a further advantage, this same pump can be operated instead with displacement-type operating characteristics. Selection of torque- or displacement-type operating characteristics can be made by the operator by means of a mode selection switch in the cab. When used with displacement-type operating characteristic, the feedback signals 252 and 254 are either not taken into account or factored down and the pump 240 is operated directly in response to the input signal 235 from the control handle 234. Although this operation of the swing in displacement mode does not provide for free coast, it may be more suitable for certain operations such as precise, small-displacement movements of the swing. Thus, the pump can be operated in either mode depending on what is most suitable for the task. The programmable controller 212 allows for the switching from torque control to displacement control at the touch of a button. 
     Referring to FIG. 6, there is depicted a schematic of one embodiment of a portion of the liftcrane control and hydraulic system for the hoist. A control handle 260 is located in the operator&#39;s cab. The control handle 260 includes a lever 262 movable across an infinite range of positions. The control handle 260 is a part of the operator controls and accordingly the control handle 260 provides an output 264 to the programmable controller 212. A hoist motor 266 is connected to the hoist drum (not shown) to effect the operation thereof. The hoist motor 266 is driven by a pump 268 to which it is connected by first and second hydraulic lines 270 and 272 (i.e. a closed loop 274). Two pressure sensors are associated with the hoist motor 266. A first pressure sensor 276 is connected to the first hydraulic line 270 and a second pressure sensor 278 is connected to the second hydraulic line 272. The first and second pressure sensors 276 and 278 are connected to the programmable controller 212 to provide first and second pressure feedback signals 280 and 282 to the programmable controller 212 indicative of the pressure on each side of the closed loop 274 connected to the hoist motor 266. In addition, a position-speed sensor 284 is responsive the movement of the hoist. The position-speed sensor 284 is connected to the programmable controller 212 to provide a feedback signal 286 thereto, indicative of the movement or position of the hoist. The routine on the programmable controller 212 compares the three feedback signals 280, 282, 286 and the signal 264 obtained from the control handle 260. The routine then generates an output 288 to the pump 268 to modify the operation of the pump, if necessary, to effect the desired operation of the hoist. 
     With this embodiment of the present invention, the programmable controller 212 can operate the hoist to synchronize brake release and pump displacement at the onset of a hoist or a lower command. This enables clam operation, for instance, to be performed with a &#34;single stick&#34;. 
     The versatility of this control system is demonstrated by the following example. One commonly performed liftcrane operation involves lifting a load with the boom and moving it to another location. This involves the steps of lowering the hoist to engage the load, lifting the load by tensioning the hoist, applying a brake to the hoist to fix the load at the height at which it has been raised, moving the load to the desired location by operation of the swing and/or the boom, releasing the brake and then lowering the load. In closed loop hoist systems when the brake is released prior to lowering the load, the load can slip or shift until sufficient pressure is induced into the hoist motor to exactly compensate for the weight of the load. This slipping or shifting can be an undesirable operating characteristic. This undesirable operating characteristic can be eliminated by this embodiment of the present invention. The liftcrane operating routine run on the controller includes the following steps: The operator in the cab manipulates the controls to hoist the load and set the brake. Operation of the appropriate controls by the operator sends signals from the controls to the programmable controller. The operation of the mechanical subsystems related to the hoist and brake are under the control of the programmable controller that carries out these operations. Upon sensing the engagement of the hoist brake, data is stored in memory indicative of a reading of the pressure sensors 276 and 278 connected to the hoist drum motor 266 at the time when the brake is engaged. This data reading is stored while the brake is engaged including during the time when the brake is engaged and the load is being moved laterally by the swing or by movement of the boom. During the period of time when the brake is engaged and the load is being moved, the pressure previously applied to the hoist motor 266 dissipates. However, when the operator operates the controls to signal to the programmable controller to release the brake, before the brake is actually released, the pressure reading stored in memory is compared to the pressure reading sensed at the hoist motor 266 by the operating routine on the programmable controller. If the pressure reading at the hoist is not equal to the reading stored in memory, the programmable controller, following the operating rountine, commands pressure to be applied to the hoist motor 266 to duplicate the pressure that was applied thereto immediately at the time the brake was engaged. When the pressure at the hoist motor 266 is sensed to be equal to the value in memory, the brake is disengaged. In this manner, unless the load changes during movement, there should be no slipping or shifting of the load when the brake is released. If the load has changed and the memory setting is too high, the position-speed sensor will detect any misdirection and the routine will operate the pump as soom as the brake is released to correct it. 
     Referring again to FIG. 4, the second preferred embodiment also includes a direct connection 290 between a set 292 of operator controls and a set 294 of mechanical subsystems to enable this set of mechanical subsystems to be operated directly by the operator controls 292 instead of being operated through the programmable controller 212. The mechanical subsystems which may be operated outside the control of the programmable controller include the boom pawl and the right and left and front and rear diverting valves. These mechanical subsystems are operated directly instead of through the programmable controller because their operation is not considered to be specifically enhanced or benefitted by computer control. The selection of mechanical subsystems operated directly may be made depending upon considerations associated with the specific use of the liftcrane. Although operation of this set 292 of mechanical subsystems is not under the programmable controller 212, switches associated with their operation may be connected to the programmable computer 212 to provide an output 296 thereto in order to provide an indication of the operation of one or more of this set 292 of mechanical subsystems. 
     In this second preferred embodiment of the present invention, a remote control panel 300 is also included. The remote control panel 300 is connected to the liftcrane by a tether cable (not shown) so that certain of the mechanical subsystems of the liftcrane can be controlled remotely, e.g. by an operator standing outside of the cab. Preferably the tether is disconnectable from the liftcrane so that the remote control panel 300 can be removed when not in use, if desired. In this second preferred embodiment, the remote control panel 300 may be used to operate certain mechanical subsystems through the programmable controller 212 and also operate certain other functions directly. Accordingly, the remote control panel 300 is connected both to the programmable controller 212 by a line 304 as well as to a set 302 of mechanical subsystems. In this embodiment, the mechanical subsystems that can be controlled directly by the remote control panel include the crawler extension, part of the gantry raising system, and the counterweight pins. The mechanical subsystems controlled by the remote control panel through the programmable controller include the boom hoist, movable counterweight and carrier and the movable counterweight beam, as disclosed in the aforementioned co-pending application, Ser. No. 07/269,222, U.S. Pat. No. 4,953,722 incorporated herein by reference. The selection of which mechanical subsystems are operated by the remote control panel through the programmable controller depends on the specific design of the liftcrane manufacturer with a consideration of the purposes for which the liftcrane will used. 
     The second preferred embodiment also includes an operator&#39;s display system connected to the programmable controller. An operator&#39;s display 310 is positioned in the cab 203 and conveys to the operator information about the status of the liftcrane mechanical subsystems. The display 310 can be a monitor of the CRT or LCD type, or the like, selected for heavy duty use. The display 310 is capable of presenting information from any of the sensors or operator controls 202 which are connected to the programmable controller 212. For example, the display 212 can show to the operator air pressure, charge pressure, engine oil pressure, main hydraulic system pressure, fuel level, battery voltage, engine water temperature, engine speed, hoist drum speed, etc. 
     Referring to FIG. 7, there is depicted a flow chart of the routine 318 that may be run on the programmable controller 212 of the second preferred embodiment of the present invention. The routine 318 is similar to the routine 48 of the previous embodiment. Like the previous routine, the routine 318 of the second embodiment includes sections of code for reading the data from the operator controls 202 and the sensors 222 and outputting commands for the mechanical systems 200. The routine of the second embodiment includes a CALL MACHINE subroutine 320 that calls the SET COMMANDS section 322 which in turn calls the REVISE COMMANDS section 324 that in turn calls a SET OUTPUTS section 326. The SET OUTPUTS section 326 returns control to the CALL MACHINE section 320 so that the routine operates in a loop and runs each of these sections in each cycle of the loop. In this preferred embodiment, the CALL MACHINE subroutine is written in Basic and the other three sections are written in machine code. A copy of the routine of the second embodiment is included in Appendix II. 
     It is intended that the detailed description herein be regarded as illustrative rather than limiting, and that it be understood that it is the claims, including all equivalents, which are intended to define the scope of the invention. ##SPC1##