Abstract:
A hydraulic function can be extended and retracted under the control of an electrohydraulic valve unit. An operator movable command lever is movable into extend, center and retract region. A sensor generates a lever position signal. An electronic lever command unit receives the lever position signal and generates a valve command signal. An electronic valve control unit is remote from and communicated with the lever command unit. The electronic valve control unit controls communication of hydraulic fluid to the hydraulic function in response to the valve command signal. A method of generating the valve command signal includes generating a command signal which is proportional to the lever position signal when the lever is moved relatively slowly, and generating a command signal which is based on a maximum excursion of the lever into the extend and retract regions when the lever is moved relatively rapidly. Command signals are transmitted to the valve control unit after a delay time period which is a fraction of a period of the lever movement oscillation.

Description:
BACKGROUND  
         [0001]    The present invention relates to a system and method for processing command signals, such as command signals for an electro-hydraulic control valve which operates a hydraulic device.  
           [0002]    It is known to provide work vehicles, such as agricultural tractors, with a loader having a bucket which is movable by a hydraulic bucket cylinder. It is known to control the bucket cylinder with a conventional electro-hydraulic (EH) selective control valve (SCV), which, in turn, is controlled by an electronic valve controller. Bucket position and movement commands are generated by a control lever which is manipulated by an operator. In some commercially available systems, the position of the lever is monitored by an electronic lever unit which is communicated with the electronic valve controller. For example, in John Deere 7030 tractors, the lever and the electronic lever unit are mounted on an armrest in the tractor cab, and the electronic lever unit is communicated with a remote valve controller via a relatively slow speed serial communications data link.  
           [0003]    In such systems, the response of the EH valve response is dependent upon the sample rate of the control lever position, the serial transmission rate of the serial data link and update rate at which the valve controller updates the valve command signal which is communicated to the SCV.  
           [0004]    Typically, with such a system the actual bucket position and movement will not accurately match the control lever position and movement because of the slow serial communications data link. In addition, delays in the system may result in SCV conditions which conflict with the control lever. In some situations, such as when it is desired to dislodge debris from a loader bucket, an operator may desire to produce a vigorous and rapid SCV response by rapidly moving the control lever. If the transmission rate of the lever position to the EH valve controller is too slow, the SCV will typically not respond as desired by the operator, and the bucket movement may not be abrupt enough to loosen the debris. During a worst case, the transmission of the lever position over the serial communications link may occur when the control lever is near its center position instead of at maximum displaced position. As a result the lever command signal may not match the actual lever position and desired movement of the bucket may not be achieved.  
         SUMMARY  
         [0005]    Accordingly, an object of this invention is to provide a system for vigorously extending and retracting a hydraulic cylinder in a system which slowly transmits command signals which are generated in response to manual movement of a control lever.  
           [0006]    Another object of the invention is to provide such a system wherein the magnitude of the command signals will be a function of the magnitude of the displacements of the lever from its center position.  
           [0007]    A further object of the invention is to provide such a system wherein the timing of command signals is a function of a frequency at which the lever is moved.  
           [0008]    These and other objects are achieved by the present invention, wherein a hydraulic function, such as a loader bucket cylinder, can be extended and retracted under the control of an electrohydraulic valve unit. An operator movable command lever is movable into extend, center and retract regions. A position sensor generates lever position signal. An electronic lever command unit receives the lever position signals and generates a valve command signal. An electronic valve control unit is remote from the lever command unit and receives the command signals via a signal transmission link. The electronic valve control unit controls communication of hydraulic fluid to the hydraulic function in response to the valve command signal. When the lever is moved relatively slowly, the lever command unit generates command signals which are proportional to the lever position signal. When the lever is moved relatively rapidly, the lever command unit generates command signals which are based on maximum excursions of the lever into the extend and retract regions. When the lever first moves from the center region into the extend or retract region, transmission of the command signal is delayed by a time delay which is related to the frequency at which the lever is oscillated back and forth between the extend and retract regions.  
           [0009]    This system provides the operator with better and more consistent control over the electrohydraulic valve. The system overcomes slow-speed or bottleneck digital communications. The system detects when the operator intends to “rattle” the bucket, and generates valve command signals which carry out this intention, despite data link limitations. As a result, performance and repeatability is greatly enhanced. For example, by allowing the operator more control over a loader bucket, the operator can more precisely control the loads. Instead of a random shaking of debris, the load can be scattered over a larger area more precisely and consistently with the controlled abruptness. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a simplified schematic diagram of a loader bucket control system according to the present invention;  
         [0011]    [0011]FIGS. 2A and 2B form a logic flow diagram illustrating an algorithm executed by the lever control unit of FIG. 1. 
     
    
     DETAILED DESCRIPTION  
       [0012]    Referring to FIG. 1, the bucket control system  10  includes a bucket  12  pivotally mounted on the end of a boom  14  which is pivoted on a frame member  16  of a vehicle or loader (not shown). The boom  14  is pivoted by a boom cylinder  18  and the bucket is pivoted by a bucket cylinder  20  connected to the boom and bucket by links  11  and  13 . Electro-hydraulic SCVs  22  control fluid flow to and from the cylinders  18  and  20 . An electronic valve control unit (VCU)  28  provides control signals to the SCVs  22  in response to signals from a boom position sensor  32 , bucket position sensor  32  and a valve command signal from an electronic lever unit  34 .  
         [0013]    An operator generates bucket command signals by manipulating a control lever  36 . Control lever  36  may be moved from a centered or neutral position into an “extend” range of positions and into a “retract” range of positions, corresponding to extension and retraction, respectively, of the bucket cylinder  20 . Lever position sensor  38  provides a lever position signal to lever unit  34 . Lever unit  34  provides a lever command signal to VCU  28  via a data link  40 , such as a serial data communication bus. Conventional rotary potentiometers could serve as the sensors  30 ,  32  and  38 .  
         [0014]    The lever unit  34  periodically, such as every 20 milliseconds, executes an algorithm  100  represented by FIGS. 2A and 2B. The conversion of this flow chart into a standard language for implementing the algorithm described by the flow chart in a digital computer or microprocessor, will be evident to one with ordinary skill in the art.  
         [0015]    In step  102  unit  34  reads and stores the current lever position value generated by sensor  38 . From a lookup table stored in a memory of unit  34 , step  104  determines a Normal Desired Command value which is preferably proportional to the lever position value read in step  102 .  
         [0016]    Step  106  determines the movement oscillation frequency F at which the lever  36  moves back and forth between its retract and extend regions. This is accomplished by using two software timers (not shown), each associated with one of the extend and retract regions. When the lever  36  moves out of either the extend and retract regions, then a) the timer associated with that region is reset and b) the value of the other timer is read and stored. Each timer is periodically decremented when the lever is not in the region associated with that timer. Ultimately, if the lever  36  is repeatedly moved back and forth between regions, the unit  34  will determine and store the total cycle time of a round trip of the lever. The inverse of this cycle time is the lever frequency F.  
         [0017]    Step  108  compares the lever frequency F to a threshold, such as 1 Hz. If lever frequency F is not greater than 1 Hz, step directs the algorithm to step  110 .  
         [0018]    Step  110  determines whether the lever  36  is in a center region, the retract region or the extend region. Step  110  directs the algorithm to step  112  if lever  36  is in the extend region, to step  114  if lever  36  is in the retract region and to step  116  if lever  36  is in the center region.  
         [0019]    Step  112 , from the stored lever positions from step  102 , determines and stores the maximum lever position Emax in the extend region, which corresponds to the farthest the lever  36  has moved into the extend region  1   
         [0020]    Step  114 , from the stored lever positions from step  102 , determines and stores the maximum lever position Rmax in the retract region, which corresponds to the farthest the lever  36  has moved into the retract region.  
         [0021]    Step  116  determines whether the lever  36  was previously in the retract, center or the extend region. Step  116  directs the algorithm to step  118  if lever  36  was previously in the retract region, to step  120  if lever  36  is previously in the extend region and to step  122  if lever  36  was previously in the center region.  
         [0022]    Step  118  calculates an average maximum retract region command value, Amax(r) as an average of the current maximum retract region lever position value Rmax, multiplied by a scaling factor C, and a stored previous Amax(r) value as follows:  
           Amax ( r )=[ Rmax +(( C− 1)× Amax ( r ))]÷ C,    
         [0023]    where the scaling factor C is preferably set to a value of 4.  
         [0024]    Step  120  calculates an average maximum extend region command value, Amax(e) as an average of the current maximum extend region lever position value Emax, multiplied by the scaling factor C, and the stored previous Amax(e) value as follows:  
           Amax ( e )=[ Emax +(( C− 1)× Amax ( e ))]÷ C.    
         [0025]    Following steps  112 ,  114 ,  116  or  118 , step  122  sets the NEW COMMAND value equal to the Normal Desired Command (from step  104 ) and directs the algorithm to step  170 .  
         [0026]    Thus, when lever  36  is being moved relatively slowly, steps  110 - 122  operate to generate a new command signal, NEW COMMAND, which is essentially proportional to the position of lever  36 .  
         [0027]    Returning to step  108 , if lever frequency F is greater than 1 Hz, step  108  directs the algorithm to step  130 .  
         [0028]    Step  130  determines a time delay value Td as a function of the lever frequency F, as follows Td=(1/F)/K, where K is an empirically determined constant, such as 8. As a result, the more rapidly the lever  36  is moved back and forth, the shorter will be the time delay value. Td is preferably a fraction of the period of the back and forth movement of lever  36 . It was found that when the lever  36  was moved at a high rate of speed a K value of 4 caused the command signal to be sent to VCU  28  well after the lever  36  had reached its maximum position. It was found that a K value of 8 worked well with both fast and slow rates of lever movement.  
         [0029]    Step  132  determines whether the lever  36  is in a center region, the retract region or the extend region. Step  132  directs the algorithm to step  140  if lever  36  is in the extend region, to step  150  if lever  36  is in the retract region, and to step  160  if lever  36  is in the center region.  
         [0030]    Step  140 , from the stored lever positions from step  102 , determines and stores the maximum lever position Emax in the extend region, which corresponds to the farthest the lever  36  has moved into the extend region.  
         [0031]    Steps  142  and  144  operate to repeatedly increment the send delay counter until the counter value reaches a value representing the time delay Td calculated in step  130 . When the time period Td has expired, then step  144  directs the alg to step  146 , which sets the NEW COMMAND value equal to the previously determined average maximum command value for the extend region, Amax(e). From step  146  control passes back to step  170 . As a result of steps  130  and  142 - 144 , the timing of the sending of command signals will be a function of a frequency at which the lever is moved.  
         [0032]    If step  132  determines that the lever  36  is in the retract region, control passes to step  150 .  
         [0033]    Step  150 , from the stored lever positions from step  102 , determines and stores the maximum lever position Rmax in the retract region, which corresponds to the farthest the lever  36  has moved into the retract region.  
         [0034]    Steps  152  and  154  operate to repeatedly increment the send delay counter until the counter value reaches a value representing the time delay Td calculated in step  130 . When the time period Td has expired, then step  154  directs the alg to step  156 , which sets the NEW COMMAND value equal to the average maximum command value for the retract, Amax(r). From step  156  control passes back to step  170 .  
         [0035]    As a result of steps  146  and  156 , the magnitude of the command signals will be a function of the magnitude of the displacements of the lever from its center position.  
         [0036]    If step  132  determines whether the lever  36  is in a center region, control passes to step  160 .  
         [0037]    Step  160  sets the NEW COMMAND value equal the OLD COMMAND value from previous operation of step  174 .  
         [0038]    Step  162  resets the send time delay counter value to zero.  
         [0039]    Step  164  determines whether the lever  36  was previously in the retract, center or the extend region. Step  164  directs the algorithm to step  166  if lever  36  was previously in the retract region, to step  168  if lever  36  is previously in the extend region and to step  102  if lever  36  was previously in the center region.  
         [0040]    Step  166 , as described with respect to step  118 , re-calculates the average maximum retract region command value Amax(r).  
         [0041]    Step  168 , as described with respect to step  120 , re-calculates the average maximum extend region command value Amax(e).  
         [0042]    Following steps  122 ,  166  or  168 , the algorithm proceeds to step  170 .  
         [0043]    Step  170  directs the algorithm to step  172  if the command value is unchanged (NEW COMMAND=OLD COMMAND) and if more than 50 milliseconds have elapsed since a command value was previously transmitted to the VCU  28 , else to step  180 . A software timer or counter “Transmit Timer” is utilized to determine the elapsed time since a command value was previously transmitted.  
         [0044]    Step  180  directs the algorithm to step  172  if Transmit Timer indicates that a full second has elapsed since a command value was previously transmitted to the VCU  28 , else to step  182 .  
         [0045]    Step  172  sends NEW COMMAND to the VCU  28 , which in turn, causes the valve unit  22  to extend or retract the bucket cylinder  12 .  
         [0046]    Step  174  sets the OLD COMMAND equal to the NEW COMMAND.  
         [0047]    Step  176  resets the Transmit Timer so the transmit timer can monitor the time expired since the operation of step  172 .  
         [0048]    After steps  180  or  176 , step  182  increments the Transmit Timer and returns the algorithm to step  102 .  
         [0049]    As a result, when lever  36  is being moved relatively slowly, steps  110 - 122  and  170 - 172  operate to transmit to VCU  28  a new command signal which is essentially proportional to the position of lever  36 .  
         [0050]    However, if the operator rapidly moves the lever  36  back and forth, steps  130 - 172  operate to cause control unit  34  to send to VCU  28  command signals which are based on maximum extend and retract positions of the lever  36 . This assures that the bucket  12  will be vigorously shaken despite slow signal transmission rates between the electronic lever unit  34  and the remote VCU  28 . The command signals will be a function of both how fast the operator is moving the control lever and also of how far away from the center the lever moves. The frequency or timing of the command signals will be a function of the frequency at which the lever is moved, and the magnitude of the command signals will be a function of the magnitude the displacements of the lever from its center position.  
         [0051]    The algorithm will attempt to transmit maximum command signals in phase with the actual lever position. For example, when the operator wishes to “shake” debris from a loader&#39;s bucket, the operator will rapidly actuate the control lever. Upon detection of rapid lever motion, the algorithm will begin transmitting a valve command based on an average peak lever position and only when the lever is near it&#39;s peak position.  
         [0052]    Steps  170 ,  180  and  182  operate to prevent transmission of a new command to VCU  28  for 1 second if the command is unchanging.  
         [0053]    Step  170  operates to transmit a new command to VCU  28  every 50 milliseconds if the command is changing.  
         [0054]    While the present invention has been described in conjunction with a specific embodiment, it is understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, this invention is intended to embrace all such alternatives, modifications and variations which fall within the spirit and scope of the appended claims.