Constant force centralizer

Abstract

A constant force device has at least a first non-constant axial force driving the first set of arms and a second non-constant axial force driving the second set of arms, where the two sets of arms are offset from one another by 90°. Each of the non-constant axial forces is converted to a radially extending force by the interaction of a force guide and actuator. The force guide is attached to the inner mandrel of the constant force device and is shaped to produce an essentially constant radially extending force through the entire range of motion of the arms. Typically each arm of the pair of arms has a pivoting arm and a telescoping arm where the joint between the pivoting arm and telescoping arm has one or more wheels to reduce friction as the constant force device moves through the tubular. Generally the first pair of arms is opposed to and overlaps by some distance the second pair of arms where the second pair of arms is 90° offset from the first pair of arms. Additional features may include friction reducing members at the joint between the telescoping arm and the pivoting arm, an extension lock, extension limiters, and rotating force guides.

What is claimed is: 
     
         1 . A constant force tool comprising,
 a pivoting force arm,   an axial biasing device,
 wherein the axial biasing device exerts an axially directed force upon the pivoting force arm, 
   a force guide mounted on a mandrel,
 wherein the force guide interacts with the pivoting force arm to convert the axially directed force to a radially directed force. 
   
     
     
         2 . The constant force tool of  claim 1  further comprising a telescoping arm wherein a first end of the telescoping arm is pivotally attached to the pivoting force arm. 
     
     
         3 . The constant force tool of  claim 2  further comprising at least one wheel mounted at the pivotal attachment between the pivoting force arm and the telescoping arm. 
     
     
         4 . The constant force tool of  claim 1  wherein, the axial biasing device is a spring. 
     
     
         5 . The constant force tool of  claim 1  wherein, the radially directed force is substantially constant. 
     
     
         6 . The constant force tool of  claim 1  wherein, the radially directed force is constant within about 10% of the maximum radially directed force. 
     
     
         7 . A constant force tool comprising,
 a pivoting force arm,   an axial biasing device,
 wherein the axial biasing device exerts an axially directed force upon the pivoting force arm, 
   a force guide rotatably mounted on a mandrel,
 wherein the force guide interacts with the pivoting force arm to convert the axially directed force to radially a directed force. 
   
     
     
         8 . The constant force tool of  claim 7  further comprising a telescoping arm wherein a first end of the telescoping arm is pivotally attached to the pivoting force arm. 
     
     
         9 . The constant force tool of  claim 8  further comprising a wheel mounted at the pivotal attachment between the pivoting force arm and the telescoping arm. 
     
     
         10 . The constant force tool of  claim 7  wherein, the axial biasing device is a spring. 
     
     
         11 . The constant force tool of  claim 7  wherein, the radially directed force is substantially constant. 
     
     
         12 . The constant force tool of  claim 7  wherein, the radially directed force is constant within about 10% of the maximum radially directed force. 
     
     
         13 . A constant force tool comprising,
 a pivoting force arm,   an axial biasing device,
 wherein the axial biasing device exerts an axially directed force upon the pivoting force arm, 
 further wherein the axially directed force is converted to a radially a directed force, and 
   an extension limiter.   
     
     
         14 . The constant force tool of  claim 13  wherein, the extension limiter prevents the pivoting force arms from extending past a predetermined maximum. 
     
     
         15 . The constant force tool of  claim 13  further comprising a telescoping arm wherein a first end of the telescoping arm is pivotally attached to the pivoting force arm. 
     
     
         16 . The constant force tool of  claim 15  further comprising at least one wheel mounted at the pivotal attachment between the pivoting force arm and the telescoping arm. 
     
     
         17 . The constant force tool of  claim 13  wherein, the axial biasing device is a spring. 
     
     
         18 . The constant force tool of  claim 13  wherein, the radially directed force is substantially constant. 
     
     
         19 . The constant force tool of  claim 13  wherein, the radially directed force is constant within about 10% of the maximum radially directed force. 
     
     
         20 . A constant force tool comprising,
 a pivoting force arm,   an axial biasing device,
 wherein the axial biasing device exerts an axially directed force upon the pivoting force arm, 
 further wherein the axially directed force is converted to a radially a directed force, and 
   a pivoting force arm lock.   
     
     
         21 . The pivoting force tool of  claim 20  wherein, the pivoting force arm lock prevents the pivoting force arms from extending prior to a predetermined event. 
     
     
         22 . The pivoting force arm tool of  claim 21  wherein, the predetermined event is exceeding a predetermined pressure differential. 
     
     
         23 . The constant force tool of  claim 21  further comprising a telescoping arm wherein a first end of the telescoping arm is pivotally attached to the pivoting force arm. 
     
     
         24 . The constant force tool of  claim 23  further comprising a wheel mounted at the pivotal attachment between the pivoting force arm and the telescoping arm. 
     
     
         25 . The constant force tool of  claim 21  wherein, the axial biasing device is a spring. 
     
     
         26 . The constant force tool of  claim 21  wherein, the radially directed force is substantially constant. 
     
     
         27 . The constant force tool of  claim 1  wherein, the radially directed force is constant within about 10% of the maximum radially directed force. 
     
     
         28 . A constant force tool comprising,
 a first pivoting force arm,   a second pivoting force arm,
 wherein a first end of the first pivoting force arm and a first end of the second pivoting force arm extend toward each other from a first end of a mandrel and from an opposing second end of the mandrel, 
 further wherein the first pivoting force arm is circumferentially offset from the second pivoting force arm, 
   a first axial biasing device that exerts a first axially directed force upon the first pivoting force arm,   a second axial biasing device that exerts a second axially directed force upon the second pivoting force arm,   a first force guide mounted on the mandrel,
 wherein the first force guide interacts with the first pivoting force arm to convert the first axially directed force to a substantially constant first radially directed force, and 
   a second force guide mounted on the mandrel,
 wherein the second force guide interacts with the second pivoting force arm to convert the second axially directed force to a substantially constant second radially directed force. 
   
     
     
         29 . The constant force tool of  claim 28  further comprising a telescoping arm wherein a first end of the telescoping arm is pivotally attached to the first pivoting force arm. 
     
     
         30 . The constant force tool of  claim 29  further comprising a wheel mounted at the pivotal attachment between the first pivoting force arm and the telescoping arm. 
     
     
         31 . The constant force tool of  claim 28  wherein, the axial biasing device is a spring. 
     
     
         32 . The constant force tool of  claim 28  wherein, the substantially constant first radially directed force is constant within about 10% of the maximum first radially directed force. 
     
     
         33 . The constant force tool of  claim 28  wherein, the substantially constant second radially directed force is constant within about 10% of the maximum second radially directed force.