Patent Publication Number: US-2009222176-A1

Title: Loader

Description:
BACKGROUND AND SUMMARY 
     The present invention relates to loaders operable to execute digging tasks or to transport and handle loads, wherein such loaders are mobile and each includes a device such as a bucket or attachment mounted onto a boom arm. Moreover, the present invention relates to arrangements for controlling such loaders. Furthermore, the invention also concerns methods of controlling such loaders and their boom arms. Additionally, the invention relates to software executable on computing hardware for implementing the methods in the aforesaid loaders. 
     Loaders are known. They are often each implemented as a four-wheeled vehicle with two substantially parallel boom arms pivotally mounted at their proximate ends towards a front region of the vehicle. A counterweight is often included at a rear region of the vehicle. Each boom arm is coupled at its distal end to a pivoting arrangement to which a device such as a bucket is coupled. Optionally, the bucket is demountable and the loader is configured to be able to accept other types of tools or attachments, in operation, such a loader is controlled by an operator or driver seated in a cabin of the vehicle. The operator or driver is provided in the cabin with controls for raising and lowering the boom arms as well as adjusting angle of the pivoting arrangement to which the bucket is coupled. Thereby, the driver is able to, for example, scoop a load, for example cement or building bricks, into the bucket and adjust an inclination of the bucket to retain its load, lift the bucket upwardly, and then drive the vehicle to another location for delivering the load held in the bucket. Alternatively, the driver can employ the bucket for digging operations, for example digging trenches and holes. 
     In view of a magnitude of physical forces required for such loaders to function, it is contemporary practice to employ hydraulic actuators, for example hydraulic cylinder actuators, for raising and lowering the boom arms, and also for adjusting an inclination angle of the pivoting arrangement associated with the bucket or attachment. Pressurized hydraulic oil for operating the hydraulic actuators is provided from a hydraulic pump coupled to an engine of the vehicle. Moreover, flow of pressurized hydraulic oil to and from the hydraulic actuators is regulated via hydraulic valves coupled appropriately to the aforesaid controls included in the cabin. As will be elucidated later, it has become contemporary practice to include sensors operable to sense orientation of the boom arms as well as orientation of the pivoting arrangement coupled to the bucket or attachment; signals provided by such sensors are coupled to a feedback arrangement employing signals from the controls in the cabin as reference signals. 
     Known loaders of a type described in overview in the foregoing will now be further elucidated. In a granted U.S. Pat. No. 4,844,685, there is described a loader including an electronic bucket positioning and control system. The loader employs a hydraulically-controlled boom arm assembly and bucket. The boom arm assembly includes a pair of boom arm lift hydraulic actuators, and a pair of bucket lift hydraulic actuators. Each hydraulic actuator includes a cylinder housing together with a piston rod movable in respect of its cylinder. Moreover, each piston includes therein a position sensor implemented as a linear potentiometer comprising a resistance strip for providing an electrical signal indicative in operation of a degree to which the piston rod is extended or retracted in respect of its corresponding cylinder. 
     In a published U.S. Pat. No. 4,923,362, there is described a boom arm and bucket system for a loader. The system includes a bucket leveling valve operable to maintain a desired orientation of the bucket as the boom arm is raised and lowered. The system employs first rotary angular sensors mounted at proximate ends of the boom arms whereat they are pivotally mounted to a vehicle body of the loader. Moreover, the system further employs second rotary angular sensors to sense an inclination of the bucket relative to the boom arm. The rotary angular sensors are conveniently implemented as potentiometers. Signals from the first and second angular sensors are coupled to an electronic feedback unit, for example implemented using computing hardware operable to execute software instructions, which compares the signals with reference signals generated from operator controls included within a cabin of the loader. In the system, the inclination angle of the bucket is directly and simply derivable from the signals generated from the first and second rotary angular sensors. 
     Of importance with regard to loaders described in the foregoing is ease of use and reliability. In view of a degree of power which operators of such loaders are able to control to execute various digging or lifting operation, it is vitally important that actuator sensors and their associated control systems are robust, for example to wear and debris generated in operation. A failure or inaccuracy in an actuator sensor implemented as a potentiometer can cause such a loader to function potentially erratically with a risk of damage to property or personnel. 
     Thus, two problems which are encountered with contemporary loaders concern robustness in use as well as dynamic handling characteristics. The first problem concerns robustness of the rotary angular sensors which can be conventionally addressed by employing a better quality of sensor. The second problem relates to reducing a risk of loads being manipulated by loaders unintentionally falling with associated potential problems of personal injury as well as damage to property; this second problem is conventionally addressed, for example as described in a European patent application EP 0 597 657, by controlling a rate at which hydraulic oil is applied or extracted from hydraulic actuators employed to actuate loader boom arms and associated buckets. 
     For aforementioned loaders, although loader operating performance has been enhanced, there is still a need for further improvements in loader performance, for example operating safety when manipulating and transporting loads, to satisfy exacting requirements demanded by contemporary users and operators of such loaders; such operating performance is a technical problem pertinent to the present invention which the present invention seeks to at least partially solve. 
     It is desirable to provide a loader with improved operating performance and operating robustness. 
     According to a first aspect of the present invention, there is provided a loader comprising a vehicle including a structural frame and at least one elongate boom arm, said at least one elongate boom arm being pivotally mounted substantially at its first end to the structural frame and having at its second end an assembly for receiving in operation one or more tools, said loader further including actuators operable to actuate said at least one boom arm and its associated assembly, and also including a control unit provided with user operable controls for controlling in operation position and orientation of the at least one boom arm and its associated assembly, characterized in that said actuators integrally incorporate therein magnetic actuator sensors operable to sense longitudinal extension of said actuators and thereby generate actuator feedback signals indicative of said longitudinal extension, wherein said control unit is operable to process said actuator feedback signals in a feedback control to render said position and orientation of said at least one boom arm and its associated assembly adjustable using said user operable controls. 
     The invention is of advantage in that the magnetic actuator sensors integrally incorporated within the actuators are capable of imparting improved operating performance and safety of operation to the loader. 
     Optionally, in the loader, the magnetic actuator sensors integrally incorporated within the actuators are each operable to sense relative positions of a piston and its associated cooperating cylinder of its corresponding actuator. Such a manner of including the actuator sensors is susceptible to increasing robustness of the actuator sensors and improving their sensing accuracy. Moreover, such magnetic sensors are found in practice to be highly robust and reliable and provide signals suitable for implementing the aforementioned feedback. 
     Optionally, in the loader, the actuators include a first actuator operable to actuate said at least one boom arm to vary its pivotal angle relative to the structural frame, and a second actuator operable to actuate said assembly to vary its pivotal angle relative to substantially the second end of said at least one boom arm. Such allocation of the first and second actuators is effective at providing a degree of isolation between local feedback loops controlling the boom arm and the assembly, thereby simplifying control and improving stability. 
     Optionally, the vehicle comprises an engine operable to provide actuation power for said actuators, said engine including an engine rotation rate sensor adapted to generate a rotation rate signal indicative of a rotation rate of said engine in operation, wherein said control unit is arranged to receive said rotation rate signal for adapting said feedback control in response to said rotation rate signal. Inclusion of the rotation rate sensor is capable of enabling the control unit to provide more stable feedback control in response to variations in engine rotation rate and hence available actuation power. 
     Optionally, in the loader, the control unit is operable to apply a mathematic translation to the actuator feedback signals to generate translated signals indicative of an inclination angle of the one or more tools and a height of the one or more tools, said translated signals being compared in the control unit with signals from the user operable controls to provide in operation said feedback control. Isolation of the control for inclination of the one or more tools relative to the control for height of the one or more tools is susceptible to rendering the loader easier to control and hence potentially safer in operation. 
     Optionally, in the loader, the feedback signals are operable to provide substantially a first order dynamic measure of angular orientations of the at least one boom arm and its associated assembly and one or more tools. Such first order dynamic response enables potentially more feedback to be applied to the loader and its assembly, irrespective of changes in their dynamic characteristics in response to varying loads being applied thereto in operation. 
     Optionally in the loader, the control unit is operable to enable the user: (a) to record one or more sets of preferred angular orientations of at least one boom arm and its associated assembly corresponding to preferred positions and orientations of the one or more tools, and (b) to invoke the one or more sets of orientations for operating said one or more tools for moving them to one or more of the preferred positions. Providing the one or more sets of preferred angular orientations and preferred position is susceptible to rendering the loader faster and easier for the user to operate, thereby potentially increasing efficiency of operation of the loader, for example when implementing repeated digging operations. 
     Optionally, in the loader, the vehicle includes an inertia! sensing unit for sensing at least one of inclination, acceleration, deceleration and vibration of said vehicle and thereby generating an inertial signal, said sensing unit being in communication with said control unit for receiving said inertial signal such that said control unit is operable to modify at least one of angular orientation and height of said one or more tools in response to said inertial signal for retaining a load borne in operation by said one or more tools more securely. Inclusion of the inertial sensing unit is capable of increasing operating safety of the loader, thereby more safely retaining and handling loads borne in operation by the loader, for example over uneven or inclined terrain. 
     According to a second aspect of the present invention, there is provided a control system including a control unit control unit adapted to control operation of a loader, said loader comprising a vehicle including a structural frame and at least one elongate boom arm, said at least one elongate boom arm being pivotally mounted substantially at its first end to the structural frame and having at its second end an assembly for receiving in operation one or more tools, said system further including actuators operable to actuate said at least one boom arm and its associated assembly, and also including the control unit provided with user operable controls for controlling in operation position and orientation of the at least one boom arm and its associated assembly, characterized in that said actuators integrally incorporate therein magnetic actuator sensors operable to sense longitudinal extension of said actuators and thereby generate actuator feedback signals indicative of said longitudinal extension, wherein said control unit is operable to process said actuator feedback signals in a feedback control to render said position and orientation of said at least one boom arm and its associated assembly adjustable using said user operable controls. 
     Optionally, in the control system, the magnetic actuator sensors are each operable to sense relative positions of a piston and its associated co-operating cylinder of its corresponding actuator. 
     According to a third aspect of the present invention, there, is provided a method of controlling operation of a loader, said loader comprising a vehicle including a structural frame and at least one elongate boom arm, said at least one elongate boom arm being pivotally mounted substantially at its first end to the structural frame and having at its second end an assembly for receiving in operation one or more tools, said loader further including actuators operable to actuate said at least one boom arm and its associated assembly, and also including the control unit provided with user operable controls for controlling in operation position and orientation of the at least one boom arm and its associated assembly, wherein magnetic actuator sensors operable to sense longitudinal extension of said actuators are integrally incorporated into said actuators, said method comprising steps of: 
     (a) generating actuator feedback signals indicative of said longitudinal extension; 
     (b) processing said actuator feedback signals in said control unit to implement a feedback control to render said position and orientation of said at least one boom arm and its associated assembly adjustable using said user operable controls. 
     Optionally, when implementing the method, the magnetic actuator sensors are each operable to sense relative positions of a piston and its associated co-operating cylinder of its corresponding actuator. 
     Optionally, in the method, step (b) further comprises steps of: 
     (c) applying a mathematical translation to the actuator feedback signals to generate translated signals indicative of an inclination angle of the one or more tools and a height of the one or more tools; and 
     (d) comparing said translated signals in the control unit with signals from the user operable controls to provide in operation said feedback control. 
     Optionally, in the method, said actuator feedback signals are operable to provide substantially a first order dynamic measure of angular orientations of the at least one boom arm and its associated assembly and one or more tools. 
     Optionally, the method includes further steps of: 
     (e) measuring using a rotation rate sensor a rotation rate of an engine of said vehicle and generating a corresponding rotation rate signal; and 
     (f) adapting said feedback control in response to said rotation rate signal to enhance stability of said feedback control. 
     According to a fourth aspect of the invention, there is provided software on a data carrier executable on computing hardware of a control unit of a loader for implementing the method according to the third aspect of the invention. 
     It will be appreciated that features of the invention are susceptible to being combined in any combination without departing from the scope of the invention as defined herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       By way of example only, embodiments of the present invention will now be described with reference to the accompanying drawings wherein: 
         FIG. 1  is a schematic illustration of an embodiment of a loader pursuant to the present invention, the loader including an actuated boom arm pivotally mounted at its proximate end to a vehicle body of the loader and pivotally coupled at its distal end to an assembly dismountably couplable to, for example, a bucket or other similar type of tool; the schematic illustration further depicts a feedback control arrangement operable to control the boom arm and its associated assembly and bucket; 
         FIG. 2  is a schematic geometrical representation of the boom arm and the assembly of the loader illustrated in  FIG. 1 ; 
         FIG. 3  is a schematic illustration of the loader depicted in  FIG. 1  in operation when manipulating a load retained within a load retaining tool of the loader; 
         FIG. 4  is a cross-sectional illustration of a hydraulic actuator employed within the loader depicted in  FIGS. 1 and 3  for actuating the boom arm of the loader or the assembly and its associated bucket of the loader; and 
         FIG. 5  is an optional modification to the loader illustrated in  FIG. 1 , wherein an inertial sensor unit, for example a configuration of accelerometers and inclination sensors, is included within a vehicle of the loader; dynamic measurement signals from the inertial sensor unit are beneficially employed to adapt control of the boom arm and the assembly for the bucket so as to increase retention of a load within the bucket, for example under braking situations or when the vehicle is negotiating uneven or unstable terrain. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , there is shown an embodiment of the present invention, namely a loader indicated generally by  10 . The loader  10  includes a vehicle denoted by  20 , the vehicle  20  being provided with four wheels, an engine  25  providing in operation motive power to one or more of the wheels, a control cabin for accommodating an operator or driver of the vehicle  20 , one or more hydraulic pumps coupled to the engine  25  and optionally a counterbalance weight; the vehicle  20  is also illustrated in  FIG. 3 . Moreover, the loader  10  comprises a boom arm and bucket arrangement which will be elucidated in further detail with reference to  FIG. 1 . 
     The boom arm and bucket arrangement is mounted to a robust mounting member  30  of the loader  10 ; the mounting member  30  serves as a support or structural frame for the boom arm and bucket arrangement. As illustrated in  FIG. 3 , the mounting member  30  is substantially located at a forward region of the loader  10  substantially in front of the aforesaid control cabin. Moreover, the boom arm and bucket arrangement comprises a boom arm  40  having a proximate end pivotally mounted at a pivot  50  onto the mounting member  30 , and also a distal end pivotally coupled to the aforesaid bucket as shown. The boom arm  40  is elongate and includes a bend portion therealong. There is also included a first hydraulic actuator  60  pivotally mounted at its first end by way of a pivot  70  to the mounting member  30 . The pivot  70  of the actuator  60  is located at a distance below the pivot  50  of the boom arm  40  as illustrated. The actuator  60  is mounted at its second end to a pivot  80  included on an interface member  90 . The interface member  90  is itself attached to the boom arm  40  at a position substantially corresponding to the aforesaid bend portion of the boom arm  40 . Towards the distal end of the boom arm  40  is included a first elongate assembly member  200  pivotally coupled at its first end via a pivot  210  to the boom arm  40 . The first assembly member  200  is further coupled at its second end via a pivot  220  to a second elongate assembly member  230  and also to a first end of a second hydraulic actuator indicated by  300 . The second assembly member  230  is coupled at its second end via a pivot  240  to a first region of a tool interfacing member  250 . The tool interfacing member  250  further includes a pivot  260  disposed in a spaced apart manner from the pivot  240 , the pivot  260  being operable to pivotally couple the tool interfacing member  250  to the aforesaid distal end of the boom arm  40 . The aforementioned second actuator  300  is pivotally mounted at its second end to a pivot  270  disposed spatially substantially midway between the pivots  240 ,  260  as illustrated. 
     The tool interfacing member  250  is adapted to releasably interchangeably receive a variety of tools and related devices. For example, the interfacing member  250  is shown in FIG.  1  coupled to the aforesaid bucket denoted by  310 ; the bucket  310  includes a base panel  320  for holding and retaining a load in operation within the bucket  310 . 
     The boom arm  40  and its associated components are controlled in operation from a control assembly denoted by  400 . The control assembly  400  includes an electronic control unit  410 ; the unit  410  is conveniently implemented using electronic hardware, for example by way of computing hardware operable to execute software instructions or dedicated hardware such as one or more application specific integrated circuits (ASICs). The assembly  400  has associated therewith an operator control console indicated by  420 ; the console  420  is coupled to the electronic control unit  410  as illustrated and will be elucidated in further detail later. The electronic control unit  410  is connected to first and second hydraulic control valves  430 ,  440  associated with the first and second hydraulic actuators  60 ,  300  respectively. The first hydraulic valve  430  includes hydraulic feed pipes or hoses  500  for injecting and extracting hydraulic oil from the first actuator  60  for actuating the first actuator  60  in operation. Similarly, the second hydraulic valve  440  includes hydraulic feed pipes or hoses  510  for injecting and extracting hydraulic fluid from the second actuator  300  for actuating the second actuator  300  in operation. 
     The vehicle  20  includes a rotation rate sensor  460  rotationally coupled to a rotating engine shaft of the engine  25  which drives the aforementioned one or more hydraulic pumps operable to provide pressurized hydraulic oil to the valves  430 ,  440 . The rotation rate sensor  460  generates in operation a rotation rate signal  470  indicative of a rotation rate, namely RPM, of the engine shaft. The rotation rate signal  470  is coupled to the control unit  410 . In operation, the control unit  410  modifies one or more of its feedback parameters, for example feedback loop gain, to improve feedback control stability in response to variations in available hydraulic power available to drive the actuators  60 ,  300 . 
     The first and second actuators  60 ,  300  include internally therein position sensors  600 ,  610  for sensing in operation position of pistons of the actuators  60 ,  300  relative to their cylinders, namely measures of effective length of the actuators  60 ,  300  between their pivots  70 ,  80 ,  220 ,  270 . The position sensors  600 ,  610  are preferably incorporated into the actuators  60 ,  300  in a manner as depicted in  FIG. 4  which will be further elucidated later. On account of the position sensors  600 ,  610  being mounted within their respective actuators  60 ,  300 , they are well protected from potential damage and degradation due to outdoor environmental conditions. Moreover, mounting the sensors  600 ,  610  within the actuators  60 ,  300  also enables better dynamic operating characteristics for the loader  10  to be achieved as will be described in further detail later. Position signals  740 ,  750  derived from the sensors  600 ,  610  respectively are conveyed in operation to the electronic control unit  410 . 
     The aforementioned console  420  includes first and second operator-adjustable controls  700 ,  710 ; conveniently, the controls  700 ,  710  are implemented as continuously moveable joy-sticks or levers although other implementations are possible. In operation, the first and second controls  700 ,  710  give rise to first and second reference signals  720 ,  730  representative of desired height and inclination tilt angle of the bucket  310  respectively. These reference signals  720 ,  730  are conveyed to the electronic control unit  410  which is operable to, in a complex manner, compare the reference signals  720 ,  730  with the position signals  740 ,  750  and thereby generate appropriate output signals  760 ,  770  to control the first and second valves  430 ,  440  respectively. 
     In comparison to contemporary known loaders described in the foregoing, the electronic control unit  410  is operable to perform more complex signal processing on account of the signals  740 ,  750  from the position sensors  600 ,  610  not being directly indicative of angular orientation of the boom arm  40  and the bucket  310 . 
     In overview, the loader  10  is operable in dynamic situations to function in a different manner to known contemporary loaders. When applying feedback in general to mechanical systems, it is known that it is more difficult to stabilize such feedback when the system in an open-loop state is susceptible to exhibiting complex multiple pole-zeroes in its frequency response. Such feedback problems are further confounded when the mechanical systems exhibit back-lash, namely “dead regions” in spatial response. Moreover, such feedback is even more difficult to optimize when system characteristics are susceptible to temporally change; for example, the boom arm  40  has elasticity and is susceptible to elastically deforming and thereby functioning as a spring denoted by K in  FIG. 2 . Substantially at the distal end of the boom arm  40  is included the bucket  310  together with its associated members  200 ,  230 ,  250  which collectively form a mass denoted by M in  FIG. 2 . This mass M is susceptible to variation depending upon a weight of a load  1200  carried in the bucket  310 . 
     A pressure of hydraulic oil provided from the one or more pumps to the valves  430 ,  440  is also a factor affecting responsiveness of the actuators  60 ,  300 , namely response time constants exhibited by the loader  10 . In order to improve user handling performance of the loader  10 , the control unit  410  is operable to vary one or more of its feedback parameters, for example one or more of its feedback loop gains, or one or more of its feedback loop time constants, in order to improve handling responsiveness and stability of the loader  10 . 
     Conventionally, to address a potentially variable open-loop system response, two approaches are possible: 
     (a) vary the feedback applied in response to changes in open-loop characteristics of a system to be controlled, namely characteristics of the boom arm  40  and its associated distal mass M; or 
     (b) apply a form of feedback which can cope with a full range of open-loop characteristics of the system to be controlled, namely characteristics of the boom arm  40  and its mass M. 
     Whereas the approach (a) represents further complexity in that dynamic response characteristics of the boom arm  40  and its mass M need to be periodically evaluated, the approach (b) results in sluggish performance which is manifest in sluggish and inaccurate response to adjustments of the first and second controls  700 ,  710  adversely affecting efficiency of use of the loader  10  and potentially reducing operating safety. 
     The inventors of the present invention have surprisingly found that the implementation of the loader  10  depicted in  FIG. 1  potentially offers considerable advantages in comparison to contemporary loaders described in the foregoing. By employing the feedback signals  740 ,  750  derived directly from the position sensors  600 ,  610  in the actuators  60 ,  300 , there is provided a direct form of feedback which is susceptible to being of a relatively lower-order system response. Such a low order system response results in the feedback being more stable and responsive. Thus, the configuration of the actuators  60 ,  300  and the control assembly  400  depicted in  FIG. 1  is capable of providing the operator of the first and second controls  700 ,  710  with more accurate and faster feedback control. Moreover, the loader  10  as depicted in  FIG. 1  would be superficially less attractive to employ in view of the complexity of signal processing required to be implemented in the control assembly  400 . 
     Referring to  FIG. 2 , there is shown a simplified geometrical representation of the loader  10  illustrated in  FIG. 1 . A parameter “a” represents a length of the first actuator  60  between its associated pivots  70 ,  80 . Moreover, a parameter “b” represents a spatial distance between the pivots  50 ,  70 . Furthermore, a parameter “c” represents a distance between the pivots  50 ,  80 . Thus, the pivots  50 ,  70 ,  80  define a triangle which, in operation, is susceptible to having its parameter “a” varied as the first hydraulic actuator  60  is actuated. At the pivot  50 , there is subtended an angle θ as illustrated. This angle θ can be described using geometry as in Equation 1 (Eq. 1): 
     
       
         
           
             
               
                 
                   θ 
                   = 
                   
                     
                       cos 
                       
                         - 
                         1 
                       
                     
                      
                     
                       ( 
                       
                         
                           
                             c 
                             2 
                           
                           + 
                           
                             b 
                             2 
                           
                           - 
                           
                             a 
                             2 
                           
                         
                         
                           2 
                            
                           
                               
                           
                            
                           bc 
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   Eq 
                   . 
                   
                       
                   
                    
                   1 
                 
               
             
           
         
       
     
     On account of the bend portion of the boom arm  40 , an orientation θd of the distal end of the boom arm  40  at the pivot  260  is described by Equation 2 (Eq. 2): 
       θ d =θ+θ 0   Eq. 2 
     wherein θ0 is a constant angular offset. In a similar manner, an angle γ associated with the bucket  310  as illustrated can be determined from geometrical analysis. The elongate member  200  has a length denoted by a parameter “e” between its associated pivots  210 ,  220 . Moreover, a distance between the pivots  210 ,  260  is denoted by a parameter “d”. Furthermore, a distance between the pivots  220 ,  240  is denoted by a parameter “f. Additionally, a distance between the pivots  240 ,  260  is denoted by “g”. All four parameters “d”, “e”, “f and “g” are substantially constant as they are determined by the lengths of their associated members  200 ,  230 ,  250  or portion of the boom arm  40 . The second actuator  300  is operable to substantially modify a spatial distance denoted by a parameter “h” between the pivots  220 ,  260  to affect changes in the angle γ. The angle γ can be substantially computed from Equation 3 (Eq. 3): 
     
       
         
           
             
               
                 
                   γ 
                   = 
                   
                     
                       
                         cos 
                         
                           - 
                           1 
                         
                       
                        
                       
                         ( 
                         
                           
                             
                               d 
                               2 
                             
                             + 
                             
                               h 
                               2 
                             
                             - 
                             
                               e 
                               2 
                             
                           
                           
                             2 
                              
                             
                                 
                             
                              
                             dh 
                           
                         
                         ) 
                       
                     
                     + 
                     
                       
                         cos 
                         
                           - 
                           1 
                         
                       
                        
                       
                         ( 
                         
                           
                             
                               g 
                               2 
                             
                             + 
                             
                               h 
                               2 
                             
                             - 
                             
                               f 
                               2 
                             
                           
                           
                             2 
                              
                             
                                 
                             
                              
                             gh 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   Eq 
                   . 
                   
                       
                   
                    
                   3 
                 
               
             
           
         
       
     
     Thus, an inclination angle α of the bucket  310  can be computed from Equations 2 and 3 as combined in Equation 4 (Eq. 4): 
     
       
         
           
             
               
                 
                   α 
                   = 
                   
                     
                       θ 
                       1 
                     
                     + 
                     
                       
                         cos 
                         
                           - 
                           1 
                         
                       
                        
                       
                         ( 
                         
                           
                             
                               c 
                               2 
                             
                             + 
                             
                               b 
                               2 
                             
                             - 
                             
                               a 
                               2 
                             
                           
                           
                             2 
                              
                             
                                 
                             
                              
                             bc 
                           
                         
                         ) 
                       
                     
                     + 
                     
                       
                         cos 
                         
                           - 
                           1 
                         
                       
                        
                       
                         ( 
                         
                           
                             
                               d 
                               2 
                             
                             + 
                             
                               h 
                               2 
                             
                             - 
                             
                               e 
                               2 
                             
                           
                           
                             2 
                              
                             
                                 
                             
                              
                             dh 
                           
                         
                         ) 
                       
                     
                     + 
                     
                       
                         cos 
                         
                           - 
                           1 
                         
                       
                        
                       
                         ( 
                         
                           
                             
                               g 
                               2 
                             
                             + 
                             
                               h 
                               2 
                             
                             - 
                             
                               f 
                               2 
                             
                           
                           
                             2 
                              
                             
                                 
                             
                              
                             gh 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   Eq 
                   . 
                   
                       
                   
                    
                   4 
                 
               
             
           
         
       
     
     wherein θ 1  is another angular offset constant. The parameters “a” and “h” are dependent on actuation of the actuators  60 ,  300  respectively. It is desired that the inclination angle α is a direct simple function of position of the control  700  and not substantially influenced by adjustment of the control  710 . 
     Moreover, from further geometrical analysis, a substantial height H of the bucket  310  above a ground level, for example as denoted on an axis  1030  in  FIG. 3 , can be computed from Equation 5 (Eq. 5): 
     
       
         
           
             
               
                 
                   H 
                   = 
                   
                     
                       H 
                       0 
                     
                     + 
                     
                       L 
                        
                       
                           
                       
                        
                       
                         sin 
                          
                         
                           ( 
                           
                             θ 
                             - 
                             
                               π 
                               2 
                             
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   Eq 
                   . 
                   
                       
                   
                    
                   5 
                 
               
             
           
         
       
     
     wherein H 0  is a height offset constant and the angle θ is as defined in Equation 1 such that the angle θ is substantially a function of a length of the first actuator  60 , and L is an effective length of the boom arm  40  from its proximate end to its distal end. 
     Equations 1 to 5 can be summarized by Equations 6 (Eqs. 6): 
       α= F   1 ( S   1   ,S   2 );  H=F   2 ( S   1 )  Eqs. 6 
     wherein S 1 , S 2  correspond to the position signals  740 ,  750  respectively. Measures of the inclination angle α and the height H derived from the position signals  740 ,  750  are compared with corresponding reference signals  720 ,  730  in the electronic control unit  410  and the signals  760 ,  770  appropriately adjusted to minimize a difference between the sensed inclination angle α and the reference signal  720 , and also to minimize a difference between the measured height H and the reference signal  730 . By doing so, the operator adjusting the controls  700 ,  710  will find that the control  700  responsively and accurately determines the inclination angle α of the bucket  310 , and the control  710  responsively and accurately determines the height of the bucket  310 . 
     It will be appreciated that the electronic control unit  410  can either employ computations to solve Equations 6 in real time, or otherwise employ pre-calculated look-up tables. 
     Operation of the loader  10  will now be further elucidated with reference to  FIG. 3 . It is found ergonomically optimal that tilt and height of the bucket  310  are independently adjustable by the operator, thereby potentially reducing a risk of accident. It is highly desirable that the control  710  only adjusts height of the bucket  310  so that its contents, namely the load  1200 , do not fall out of the bucket  310  when the boom arm  40  is adjusted in position. As illustrated in  FIG. 1 , the base panel  320  of the bucket  310  has a slight front upwardly-curved lip for assisting in retaining the load  1200  within the bucket  310 . In  FIG. 3 , the aforesaid counterbalance is denoted by 1000. Dynamic mechanical characteristics of the loader  10  are not only affected by a weight of the load  1200  carried within the bucket  310  but also, to a lesser extent, by a weight of the counterbalance  1000 . When the bucket  310  is provided with an extension  1020  as illustrated in  FIG. 3 , it is especially desirable that accurate control of the inclination angle α is achieved. 
     The loader  10  is susceptible to function in both a transportation mode as well as a digging mode. In the transportation mode, the member  250  is beneficially provided with a fork arrangement as depicted in  FIG. 3 ; this fork arrangement can either be additional to the bucket  310  or in substitution thereof. In the transportation mode, the electronic control unit  410  is configured to be able to maintain a substantially constant inclination angle α in response to different heights H selected by the operator using the control  710 ; in other words, parallelism of the work piece is maintained in operation. For enhancing safety, a table of lifting capacities as a function of lifting height H can be stored in the electronic control unit  410 ; the electronic control unit  410 , for purposes of enhancing operating safety, can intentionally limit the height H demanded by the operator using the control  710  so that the loader  10  is not operated beyond its safe range of operation. Optionally, the electronic control unit  410  is operable to inform the operator when the unit  410  intentionally limits operation to the limited height H. As a further refinement, the electronic control unit  410  can be configured to limit a rate at which the load  1200  is lowered, namely a rate at which H is reduced, so as to avoid shock damage to the load  1200 . 
     Conversely, in the digging mode of operation, limits to a range of heights H through which the bucket  310  is capable of being manipulated are stored in memory of the electronic control unit  410 , for example a highest position and a lowest position. Similarly, maximum and minimum inclination angles α achievable for the bucket  310  can also be stored in the electronic control unit  410 . These limits can be stored as preset positions which the operator can invoke by pressing appropriate control switches or similar. For example, there can be provided a “return to dig” control to enable the operator to rapidly invoke a stored and therefore memorized digging position for the bucket  310 . 
     A further refinement to the loader  10  is illustrated in  FIG. 5 . The vehicle  20  of the loader  10  is further provided with an inertial sensor unit  5000 . In its simplest implementation, the sensor unit  5000  is operable to measure inclination of the vehicle  20 , for example when operating over uneven or sloping terrain. A vehicle inclination indicative signal present in an output signal  5010  from the sensor unit  5000  is beneficially, for example in the aforementioned transportation mode of operation, applied to modify the reference signal  720  controlling the inclination angle α of the bucket  310  so as to generate via a summing function  5020  a modified reference signal  5030  for use in controlling the first and second actuators  60 ,  300 . By appropriately modifying the desired inclination angle α, operating safety of the loader  10  is potentially improved when operating over inclined or uneven terrain. As a further modification, the sensor unit  5000  also includes one or more accelerometers and wheel sensors for measuring forward or reverse speed of the vehicle  20  and also a rate of deceleration or acceleration demanded by the aforesaid operator when operating the loader  10 . In response to the acceleration and deceleration, and also in response to a direction of travel of the vehicle  20 , namely forward or reverse, the desired inclination angle α of the bucket  310  can be momentarily modified so as to retain the load  1200  more safely within the bucket  310 . For example, when the vehicle  20  is traveling in a forward direction and is subject to deceleration, the inclination angle α is beneficial momentarily increased during deceleration so that the load  1200  is less likely to be ejected from the bucket  310 . Similarly, when the vehicle  20  is traveling in a reverse direction and is subject to acceleration, the inclination angle α is beneficial momentarily increased during acceleration so that the load  1200  is less likely to be ejected from the bucket  310 . Such compensation of the inclination angle α in response to measurement signals provided from the sensor unit  5000  is optionally selectable by the operator in a situation where the operator deliberately accelerates the vehicle  20  rapidly backwards for dislodging and hence depositing the load  1200 . Furthermore, when the sensor unit  500  includes accelerometers, a measurement of an unevenness of a terrain over which the vehicle  20  is traveling can be ascertained in order to automatically reduce the height H at which the load  1200  is carried and/or increase the inclination angle α so as to reduce a risk of accident or unintentional dropping of the load  1200 . As elucidated in the foregoing, inclusion of the rotation rate sensor  460  enables the control unit  410  to modify one or more feedback parameters influencing the signals  760 ,  770  and thereby improving stability and hence operating safety of the loader  10 . 
     It will be appreciated from the foregoing that the present invention is not only capable of providing the operator of the loader  10  with more precise and stable control of the load  1200 , but is also capable of increasing operator safety, both when the loader  10  is stationary and when transporting the load  1200  between locations. Such enhancement would not be contemporarily anticipated in that more comprehensive feedback around configurations of mechanical components would be perceived to be a logical approach to improving performance. 
     In order that the present invention is comprehensively described, implementation of the actuators  60 ,  300  will elucidated with reference to  FIG. 4 . In  FIG. 4 , a cross-sectional view of the actuators  60 ,  300  is provided. Each actuator  60 ,  300  comprises a first end substantially circular housing eye  2000  comprising a central mounting hole  2005 , and also a second end substantially circular housing eye  2010  also comprising a central mounting hole  2015 . The first end housing eye  2000  is attached to a proximate end of a piston rod  2020 . Substantially at a distal end of the piston rod  2020  is included a piston  2030  implemented as an annulus surrounding the piston rod  2020 . The piston rod  2020  has formed therein an elongate central hole as shown, the central hole having an opening at the distal end of the piston rod  2020 . Moreover, the second housing eye  2010  is attached to a proximate end of a cylinder  2040 , the cylinder  2040  having at its distal end an integral annular collar providing a hydraulic seal to an outer surface of the piston rod  2020 . An outer annular surface of the piston  2030  is operable to provide a hydraulic seal to an inner surface of the cylinder  2040  as illustrated. Thus, in operation, the first housing eye  2000  together with its piston rod  2020  and its piston  2030  are capable of sliding relative to the cylinder  2040  and its associated second housing eye  2010 . In the cylinder  2040 , the piston  2030  is operable to define first and second chambers  4000 ,  4010  which are preferentially supplied with hydraulic oil under pressure in order to actuate the piston  2030  and hence the piston rod  2020  relative to the cylinder  2040 . 
     The aforesaid sensors  600 ,  610  are implemented for each actuator  60 ,  300  by way of a magnetic transducer  3000  provided with a robust electrical connection  3010  at a peripheral surface of the second housing eye  2010 . The aforesaid signals  740 ,  750  are derived via the electrical connections  3010  of the actuators  60 ,  300  respectively. The transducer  3000  includes a central shaft  3020  adapted to be accommodated within the aforesaid central hole of the piston rod  2020 . Substantially at the distal end of the piston rod  2020 , at an inside surface of the central hole thereof, an annular magnetic component  3030  is included. In operation, the magnetic component  3030  slides together with the piston rod  2020  relative to the central shaft  3020  thereby modifying a magnetic characteristic of the transducer  3000 . Such modification of the magnetic characteristics of the transducer  3000  provides a measure of relative position of the piston rod  2020  relative to the central shaft  3020  and hence an indication of a length of the actuator between its housing eyes  2000 ,  2010 . Either changes in inductance or change in magnetic field strength experienced by the transducer  3000  are used to generate the signals  740 ,  750 . Use of magnetic sensing is found to be especially robust in practice, especially in view of the cylinder  2040  being operable to provide magnetic shielding for the transducer  3000 , and relatively insignificantly affected by trace hydraulic oil and other debris arising within the actuators  60 , 300  during prolonged periods of use. 
     Modifications to embodiments of the invention described in the foregoing are possible without departing from the scope of the invention as defined by the accompanying claims. 
     Expressions such as “including”, “comprising”, “incorporating”, “consisting of, “have”, “is” used to describe and claim the present invention are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural. 
     Numerals included within parentheses in the accompanying claims are intended to assist understanding of the claims and should not be construed in any way to limit subject matter claimed by these claims.