Patent Application
20070271762
Referring to
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.
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.
Referring now to
Referring again to
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.
Referring now to
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.
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.
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.
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.
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.
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.
