Abstract:
A system and method for stressing tendons includes a hydraulically actuated puller configured to pull a tendon extending from a structure and a user input configured to receive a user-desired stressing parameter indicating at least one of a desired stressing magnitude and desired stressing distance. A processor is included that is configured to receive the user-desired stressing parameter from the user input and control the hydraulically actuated puller to apply at least one of the desired stressing magnitude and the desired stressing distance to the tendon.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of International Application No. WO 2005US0003769 filed Feb. 4, 2005, published as WO 05076980, and entitled “HYDRAULIC TORQUE WRENCH SYSTEM.” 
       FIELD OF THE INVENTION 
       [0002]    This invention relates to tensioning or stressing tendons extending from a structure and, in particular, to a system and method for automatically stressing mono-strand tendons used in construction processes. 
       DISCUSSION OF THE PRIOR ART 
       [0003]    Concrete is a common building material that is often used to form the primary structural components of many structures. In such structures, mono-strand tendons are often used to strengthen the overall structure. For example, mono-strand tendons are often employed in slab-on-grade foundations, elevated parking garages, multi-story buildings, and large formed tanks to create an active reinforcement system that is generally superior to passive reinforcement systems, such as re-bar. 
         [0004]    To create an active reinforcement system using mono-strand tendons, a tendon is fed through a passage formed in a portion of the structure, a stress is applied to the tendon, and the stressed tendon is secured. To stress the tendons, an operator controls a hydraulic jack that pulls the tendon. Prior to stressing the tendon, the operator must measure the size and length of the tendon and, using the structural design requirements, determine an elongation of the tendon required to maximize reinforcement of the structure as well as the life of the tendon. The operator must then relate the hydraulic pressure of the jack to the stress applied to the tendon so that the user can estimate whether the desired elongation has been achieved. Accordingly, during the stressing process, the operator must monitor the hydraulic jack to determine when it has reached a pre-determined hydraulic pressure that the operator has correlated to an amount of stress that should be applied to the tendon. 
         [0005]    Alternatively, some hydraulic jack systems include mechanical measuring devices that are designed to measure the elongation of the tendon as it is stressed. These mechanical measuring devices typically include a counter that is rotatably incremented by the tendon as it is elongated. In this regard, the counter provides the user with a measure of the elongation. These measuring systems, while eliminating the need for the operator to equate the hydraulic pressure to the elongation of the tendon, require the operator to carefully monitor and control the hydraulic jack during the stressing process. 
         [0006]    Therefore, it would be desirable to have a system and method to reduce the amount of calculations, oversight, and control that an operator must perform during stressing of a mono-strand tendon. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention overcomes the aforementioned drawbacks by providing a system and method for automatically controlling a process for stressing a mono-strand tendon. In particular, a user input is designed to receive a user-desired parameter indicating an amount of elongation to be applied to a tendon. A processor is included that receives the user-desired parameter from the user input and automatically controls a hydraulic jack to accurately stress the mono-strand tendon according to the user-desired parameter. 
         [0008]    In accordance with one embodiment, a system for stressing a tendon is disclosed that includes a hydraulically actuated puller configured to grip a tendon extending from a structure. A user input is included that is configured to receive a user-desired stressing parameter indicating a desired stressing magnitude or a desired stressing distance. A processor receives the user-desired stressing parameter from the user input and controls actuation of the hydraulically actuated puller to apply the desired stressing magnitude or the desired stressing distance to the tendon. 
         [0009]    In accordance with another embodiment, a hydraulic stressing system is disclosed that includes a gripper configured to engage a tendon extending from a structure and a hydraulically actuated puller configured to pull the gripper to elongate the tendon during a stressing process. A sensor is configured to determine an actual elongation of the tendon during the stressing process. A user input is included that accepts a user-selected stressing parameter indicating a desired elongation of the tendon to be achieved during the stressing process. The system also includes a processor that is programmed to receive the user-selected stressing parameter indicating the desired elongation of the tendon from the user input and receive feedback from the sensor indicating the actual elongation of the tendon. Accordingly, the processor controls the stressing process to match the actual elongation of the tendon to the desired elongation of the tendon. 
         [0010]    In accordance with yet another embodiment, a hydraulic stressing system is disclosed that includes a gripper configured to engage a tendon extending from a structure and a hydraulic jack configured to pull the gripper to elongate the tendon during a stressing process. A pump is configured to provide fluid to the hydraulic jack to cause the hydraulic jack to pull the gripper and a pump sensor is provided that monitors an actual pressure applied at the pump. A position sensor is included that is designed to monitor an actual elongation of the tendon during the stressing process. A processor is provided to control the pump to increase the fluid provided to the hydraulic jack according to a desired pump pressure. The processor then receives feedback from the pump sensor indicating the actual pump pressure of the pump as well as feedback from the position sensor indicating the actual elongation of the tendon resulting from the actual pump pressure. Accordingly, the processor calculates whether any slack in the tendon has been removed using the desired pump pressure, the actual pump pressure, and the actual elongation of the tendon. 
         [0011]    Various other features of the present invention will be made apparent from the following detailed description and the drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a perspective view of a hydraulic tensioning system in accordance with the present invention engaged with a tendon; 
           [0013]      FIG. 2  is a schematic diagram of the hydraulic and electronic systems of the hydraulic tensioning system of  FIG. 1 ; 
           [0014]      FIG. 3  is a plan view of a user interface of the hydraulic tensioning system of  FIG. 1 ; and 
           [0015]      FIG. 4  is a flowchart setting forth the steps for stressing a tendon using the hydraulic tensioning system of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]    Referring to  FIGS. 1 and 2 , a hydraulic tensioning system  10  includes a power unit  12  and a puller  14 . The power unit  12  has a hydraulic pump  16 , which may be a fixed displacement pump, driven by an electric motor  18  to supply hydraulic fluid under pressure through a valve  20 , which may also be manually operable or, as shown, a four-way, two-position valve operated by two solenoids  21 ,  23 . The pump  16  draws fluid from a reservoir tank  22 , to which fluid is returned from the puller  14  by the valve  20 . In the position of the valve  20  illustrated in  FIG. 2 , fluid under pressure from the pump  16  is directed to a retract port B of the puller  14  and from an advance port A of the puller  14  to the tank  22 . When the valve  20  is shifted by the solenoids  21 , 23  to its other position, fluid under pressure from the pump  16  is directed to the advance port A of the puller  14  and from the retract port B of the puller  14  to the tank  22 . The system  10  also includes a pressure relief valve  24  that prevents the pressure in the retract line from exceeding a preset limit. 
         [0017]    The power unit  12  also includes a pressure transducer that acts as a pump pressure sensor  26  to produce an electrical signal representative of pump pressure, which is provided to a microprocessor that acts as a controller  28 . The pressure sensor  26  measures the pressure upstream of the valve  20  and provides feedback to the controller  28  to determine the cycling set points of the solenoids  21 ,  23  and the valve  20  during normal system operation. 
         [0018]    The controller  28  also receives feedback from a user input  30  and supplies information to a display  32 , for example liquid crystal display (LCD) screen, that is configured to display user-desired parameters input through the user input  30  or other information output from the controller  28 . In particular, the controller  28  monitors operator inputs from the user input  30 , torque wrench pressure as measured by the pressure sensor  26 , and a variety of other system status indicators and sensors to control the system  10  and provide outputs to the display  32 . The controller  28 , user input  30 , and display  32  may all be considered part of the power unit  12 , although they may be connected to the power unit  12  and to each other by cables that can be unplugged. 
         [0019]    Referring now to  FIGS. 2 and 3 , the controller  28  controls operation of the pump motor  18  and the valve  20  solenoids  21 ,  23  based on user-desired parameters received from the user input  30 . The user input  30  typically includes multiple buttons. In particular, a menu button  35  is included to allow an operator to toggle between various display modes, select particular data sets to be displayed on the display  32 , and select between automated or manual tensioning processes. Two other buttons  36 ,  37  include “UP” and “DOWN” arrows, respectively, and can be used for a variety of purposes. For example, when operating in the manual mode, the UP button  36  and the DOWN button  37  provide feedback to the controller  28  indicating the direction the operator desires the puller  14  to actuate. On the other hand, when in the automated mode, as will be described with respect to  FIG. 4 , the UP button  36  and the DOWN button  37  are used to input desired stressing parameters that the controller  28  uses to automatically control the system  10 . In this regard, it is contemplated that during a setup process, when the operator is inputting the desired stressing parameters, the display  32  will show the current stressing parameter as a particular value, for example, a numerical indication of the desired pounds per square inch (PSI)  39  shown in  FIG. 3 . Following the setup process, the display  32  may then be used to display the current operating conditions calculated by the controller  28  during the automated stressing process. Finally, a power button  38  is included that operates to turn the system  10  off and on. Alternatively, it is contemplated that the user input  30  may be modified to include additional keys or even a complete computer keyboard for setting input parameters, calibrating, or making other settings for the system  10 . 
         [0020]    Referring again to  FIGS. 1 and 2 , the puller  14  may be of any suitable type. However, it is contemplated that the puller  14  is designed for extremely rugged and heavy-duty service, for example, having a metal body  40  that houses a hydraulic cylinder  42  and a piston  44  that is slideably received in the cylinder  42  to reciprocate axially as hydraulic fluid is introduced to the cylinder  42  at either the advance A or retract B lines. The piston  44  drives a gripper  45  back and forth to pull a post or tendon  46 . 
         [0021]    A position sensor  48  is included within the body  40  and is positioned to monitor the tendon  46  as it is pulled from a structure  50  and elongated by the system  10 . The sensor may preferably be a linear variable differential transducer or displacement transducer. In this regard, a feedback line  52  is included to allow the sensor  48  to provide feedback to the controller  28  in order to determine when the system  10  has sufficiently stressed the tendon  46  according to the user selected parameters input through the user input  30 . 
         [0022]    Referring now to  FIG. 3 , an automated process  60  for stressing or tensioning a tendon using the above-described system starts  62  upon receiving user-desired stressing parameters and/or tendon characteristics  64 . As previously described, this information may be input through a user interface to indicate the final parameters the user desires upon completion of the stressing or tensioning process. These parameters may take various forms and may include, for example, a desired stressing magnitude or a desired stressing distance. In particular, the parameters may simply include a desired elongation that the operator whishes to achieve at the outcome of the stressing process or may include a desired pressure to be applied to the tendon and/or the characteristics of the tendon. In the latter case, the operator provides the characteristics of the tendon and construction, and relies upon the controller to calculate the desired elongation that would be appropriate for a tendon having the characteristics indicated by the operator. In any case, upon receiving these parameters  64 , the controller determines the specific control parameters  66  required to achieve the desired outcome. 
         [0023]    Before initiating the stressing process, the system determines whether the stress level currently applied to the tendon is negative  68 . This may be achieved by analyzing the feedback provided to the controller by the pressure sensor monitoring the pressure of the hydraulic fluid in the system. The controller can engage the motor to cause the pump to increase the pressure in the system slightly. In this regard, if the increased pressure results in movement of the tendon without sufficient resistance, the controller will determine that the stress level was negative  70  as a result of slack in the tendon. The controller will then incrementally increase the pressure in the system until the tendon provides adequate resistance indicating that the slack has been removed  72 . 
         [0024]    Once all of the slack in the tendon has been removed  72  or if there is initially no slack in the tendon  74 , the controller resets the current tendon displacement reference point to zero  74 . In this regard, any feedback previously received from the position sensor monitoring the displacement of the tendon through the puller is disregarded. This allows the controller to control the system based on a highly accurate measurement of tendon elongation that would otherwise include errors due to the inclusion of feedback provided during the removal of slack from the tendon. 
         [0025]    With the reference displacement point set reset  76 , the system can begin stressing the tendon  78 . During the stressing process, the controller continually determines whether the current stress applied to the tendon meets the desired stressing parameters entered by the operator  64  by first determining if the stress applied and/or elongation achieved is less than the desired stress/elongation  80 . This determination  80  may be performed using the positioning feedback provided by the sensor monitoring the elongation of the tendon and/or using the current pressure applied to the tendon. In the latter case, the controller may use the characteristics of the tendon entered by the operator to determine whether, under the pressure levels currently being applied, the tendon should be sufficiently stressed along with the actual elongation measured by the positional sensor. Regardless of how the current stress level and/or elongation is determined, if the controller determines that the current stress being applied has not achieved the desired stress/elongation  82 , the system continues increasing the stress applied to the tendon  78  until the current stress applied/elongation achieved is not less than the desired stress/elongation  84 . 
         [0026]    Once the current stress applied/elongation achieved is not less than the desired stress/elongation  84 , the controller determines if the current stress/elongation is greater than the desired stress/elongation  86 . If so  88 , the controller reverses the system to reduce the stress applied to the tendon  90  and then determines whether the current stress/elongation is neither less than the desired stress/elongation  80 ,  84  nor greater than the desired stress/elongation  86 . If so  92 , the system has sufficiently stressed to tendon according to the user-desired stressing parameters  64  and the controller automatically ends the stressing process  94 . 
         [0027]    Therefore, a system and method for automatically stressing/tensioning mono-strand tendons is achieved. The system is capable of applying a predetermined/user-selected tension to a tendon with increased accuracy over prior art systems that rely on the operator to continuously monitor the stressing process and determine when the desired elongation has been achieved. Furthermore, the present invention is significantly more accurate than prior art systems that do not account for removing any slack in the tendon before initiating the stressing process. 
         [0028]    The present invention has been described in terms of the preferred embodiments, and it should be appreciated that many equivalents, alternatives, variations, and modifications, aside from those expressly stated, are possible and within the scope of the invention. Therefore, the invention should not be limited to a particular described embodiment.