Patent Publication Number: US-8979425-B2

Title: Screed extender speed control

Description:
TECHNICAL FIELD 
     The present disclosure relates to an extendable screed, and more particularly to an electro-hydraulic control system associated with the extendable screed. 
     BACKGROUND 
     Typically, pavers utilize extendable screed assemblies to widen an effective paving width. The screed assembly includes a main screed and an extendable screed movably attached to the main screed. An electro-hydraulic system is provided to extend or retract the extendable screed relative to the main screed. The electro-hydraulic system includes an on/off switch to move and stop the extendable screed at a desired width of paving. However, during operation, a greater control is required to move and vary the width of paving using the extendable screed. There is a need for improved electro-hydraulic control system to vary the speed of the extendable screed during operation. 
     SUMMARY 
     In one aspect, the present disclosure provides a screed assembly including a main screed, an extendable screed movably attached to the main screed, and a control system for the extendable screed. The control system includes a first input device, a second input device, a third input device, and a controller. The first input device configured to set a speed limit for the extendable screed, and the second input device configured to vary a speed of the extendable screed within the speed limit. Further, a third input device configured to govern a relationship between a speed of the extendable screed and a relative position of the second input device. Based on the inputs received from the first, the second, and the third input devices the controller outputs a command signal to move the extendable screed relative to the main screed. 
     In another aspect, the present disclosure provides a method for moving the extendable screed relative to a main screed. The method includes steps of producing a limiting signal and a control signal from the first input device and the second input device, respectively. The limiting signal is indicative of the speed limit for the extendable screed and the control signal varies the speed of the extendable screed within the speed limit. The method further includes a step of selecting a modulation curve by a third input device for varying a relationship between a speed of the extendable screed a relative position of the second input device. The method outputs a command signal using the controller, based on the limiting signal, the control signal, and the modulation curve to move the extendable screed relative to the main screed. 
     Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a paver having a screed assembly; 
         FIG. 2  is a rear view of the screed assembly of  FIG. 1 ; 
         FIG. 3  is a block diagram of a control system for the screed assembly of  FIG. 1 ; 
         FIG. 4  illustrates a flow chart for a method of moving an extendable screed; and 
         FIG. 5  illustrated an exemplary curve between a speed of the extendable screed and a relative position of a second input device. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure describes a system and method for speed control of an extendable screed, according to an aspect of the present disclosure.  FIG. 1  illustrates a side view of a paver  100 , according to an embodiment of the present disclosure. The paver  100  may be a crawler track type or rubber tire type. The paver  100  includes a screed assembly  102  having a main screed  104  and an extendable screed  106 . The main screed  104  may be connected to an end of a tow arm  108 . The other end of the tow arm  108  may be pivotally connected to the chassis  110  of the paver  100  in a manner for towing the screed assembly  102 . The extendable screed  106  is movably attached to the main screed  104 . In an embodiment, the main screed  104  may include a screed extension carriage  112 , for mounting the extendable screed  106 . The extendable screed  106  may be mounted rearwardly of the main screed  104 . However, the extendable screed  106  may be mounted in front of the main screed  104 . 
     Moreover, the main screed  104  may also include a mechanism to control pavement slope and/or crown of a screed plate carried by the main screed  104 . In an embodiment, the main screed  104  may include two sections, one on each side of a center line of the paver  100 . Accordingly, the extendable screed  106  may be symmetrically mounted to the each section of the main screed  104 . It will be apparent to a person skilled in the art that the screed assembly  102  is symmetrical with respect to the center line of the paver  100 , and the present disclosure will be described with reference to only one section of the main screed  104  and the associated extendable screed  106 . 
     The paver  100  may include a paver operator station  114 , and a screed operator station  115 . The paver operator station  114  is used for controlling various functions in the paver  100  and also few functions associated with the screed assembly  102 , while the screed operator station  115  primarily used to control the screed assembly  102  The paver operator station  114  may include seats  116  for operators. Further, the paver operator station  114  and the screed operator station  115  may include respective user interfaces  118 ,  120 . The user interfaces  118  and  120  may be used for accepting various inputs from the operator and also displaying information to the operator. 
     A rear view of the screed assembly  102  is illustrated in  FIG. 2 . In an embodiment, a hydraulic system  200  is provided for extending and retracting the extendable screed  106  relative to the main screed  104 . The hydraulic means  200  includes a hydraulic cylinder  215  for extending and retracting the extendable screed  106  relative to the main screed  104 . 
       FIG. 3  illustrates a block diagram of a control system  300  for the extendable screed  106 , according to an embodiment of the present disclosure. The control system  300  includes a controller  302 , a first input device  304 , and a second input device  306 . The first input device  304  and the second input device  306  may include the user interface display, dials, rollers, pedals, joy-sticks, switches, lever, push buttons, or the like. The first and the second input devices  304 ,  306  may be incorporated within the user interfaces  118  and  120  for accepting various inputs from the operator. In an embodiment, the first and the second input devices  304 ,  306  may be incorporated within a same device, such as a joy-stick, a user interface display, dials, lever etc. 
     The controller  302  is configured to receive operator control signals, based on the input from the operator, from the first input device  304  and the second input device  306 . The controller  302  may be a microprocessor based system that output a command signal based on the received operator control signals. The command signal is received by an electrohydraulic control valve  308 . The electrohydraulic control valve  308  may be a solenoid actuated valve and configured to control a flow of hydraulic fluid to the hydraulic cylinder  215  to extend and retract the extendable screed  106  relative to the main screed  104 . Further, a position sensor  310  may be provided to measure a linear extension of the hydraulic cylinder  215  and send a position signal to the controller  302 . The position sensor  310  may be one of several well known linear displacement transducers. 
     In an embodiment, the first input device  304  may be configured to set a speed limit for the extendable screed  106 . Various sensors associated with the first input device  304  may produce an operator control signal, such as a limiting signal indicative of a speed limit of the extendable screed  106 . In an embodiment, the speed limit of the extendable screed  106  may include discrete values, such as low speed, medium speed, and high speed. In another embodiment, the speed limit of the extendable screed  106  may be selected from various continuous values with a gradual increase from the low speed to a maximum speed. In an embodiment, the second input deice  306  may be configured to vary a speed of the extendable screed  106  within the speed limit. The second input device  306  may produce another operator control signal, such as a control signal to vary the speed of the extendable screed within the speed limit. In an embodiment, the control signal may be based on a relative position of the second input device  306  set by the operator. The relative position of the second input device  306  may include a rotational, linear, or angular position of the second input device  306 , such as a dial, roller, pedal, joy-stick, lever etc., with respect to an initial position. 
     The controller  302  may include a system memory  312  and a processor  314 . The system memory  312  may include for example, but not limited to, a Random Access Memory (RAM), a Read Only Memory (ROM), flash memory, a data structure, and the like. The system memory  312  may store a computer executable code to compute the speed of the extendable screed  106  based on the limiting signal, and the control signal received from the first input deice  304  and the second input device  306 , respectively. The system memory  312  may be operable on the processor  314  to compute the speed of the extendable screed  106 . In an embodiment, the processor  314  may be configured to compute the speed of the extendable screed  106  as a percentage of the speed limit in response to the relative position of the second input device  306 . In an embodiment, the speed of the extendable screed  106  may be linearly proportional to the relative position of the second input device  306 . For example, at 50% relative position of the second input device  306 , the speed of the extendable screed  106  is substantially equal to 50% of the speed limit. 
     In another embodiment, the speed of the extendable screed  106  may be non-linearly proportional to the relative position of the second input device  306 . In an embodiment, the control system  300  may further include a third input device  316  configured to govern a relationship between the speed of the extendable screed  106  and the relative position of the second input device  306 . The third input device  316  device may include a dial, user interface display, switch, push button etc. Further, the third input device  316  may be also incorporated with the second input device  306 . In an embodiment, a linear or a non-linear relationship may be achieved by modification of a modulation curve governing the relationship between the speed of the extendable screed  106  and the relative position of the second input device  306 . 
     Moreover, it may be understood to a person skilled in art that the controller  302  may be integrated with various input and output devices associated with the other operations of the paver  100 , such as travel, steering, braking etc. The controller  302  may also include a display unit to display various parameters associated with the paver  100 , such as travel speed, slope, height, and extension of the screed assembly  102 . 
     INDUSTRIAL APPLICABILITY 
     The control system  300  described above allows the operator to controllably vary the speed of the extendable screed  106  within the set speed limit. Moreover, the control system  300  may also allow selecting the modulation curve to further control the variation in the speed of the extendable screed  106  within the speed limit. 
       FIG. 4  illustrates a method  400  for moving the extendable screed  106 . In step  402 , the operator may set the speed limit, for example low speed, medium speed, or high speed using the first input device  304 . The first input device  304  may produce the limiting signal and sends to the controller  302 . In an embodiment, the limiting signal may limit an output of a pressurized hydraulic fluid source, such as a hydraulic pump. Accordingly, a pressure and a volume of the hydraulic fluid which enters the hydraulic cylinder  215  limit a maximum speed of the extendable screed  106 . 
     In the following step  404 , the operator may produce the control signal using the second input device  306  to vary the speed of the extendable screed  106  within the speed limit, the maximum speed. According to an aspect of the present disclosure, at step  406 , the operator may select the modulation curve using the third input device  316  to vary the relationship between the speed of the extendable screed  106  and the relative position of the second input device  306 . In the following step  408 , the controller may receive the limiting signal, the control signal, and the modulation curve to output the command signal. In an embodiment, the command signal may control the electrohydraulic control valve  308  to vary the flow of pressurized hydraulic fluid to the hydraulic cylinder  215 . 
       FIG. 5  illustrated an exemplary curve  500  between the speed of the extendable screed  106  and the relative position of the second input device  306 . Along X-axis, the relative position of the second input device  306  may vary from 0% to about 100%. Along Y-axis, the speed of the extendable screed  106  may increase from zero to a maximum speed. Further, based on the input received from the first input device  304  the speed limit for the extendable screed  106  may be set to two or more values, whereas in this case  502 ,  504 , and  506  represent low speed, medium speed, and high speed respectively. 
     In an embodiment, the operator may select the low speed limit  502  using the first input device  304 . Following the same, the operator may change the relative position of the second input device  306  to vary the speed of the extendable screed  106  within the low speed limit  502  along a substantially linear curve  508 . Moreover, the operator may also select a modulation curve  510  using the third input device  316  to vary the speed of the extendable screed  106 . The modulation curve  510 , as illustrated, may be parabolic and positioned outwardly with respect to the linear curve  508 . Thus, when the operator moves the second input device  306  to 50%, the speed of the extendable screed  106  may be greater than 50% of the low speed limit  502 . In another embodiment, the modulation curve  510  may be positioned inwardly with respect to the linear curve  508 . This gives the operator better speed control for the extendable screed  106  during operation. 
     Although the embodiments of this disclosure as described herein may be incorporated without departing from the scope of the following claims, it will be apparent to those skilled in the art that various modifications and variations can be made. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.