Real-Time Control of Twist Deformation

Abstract

In many areas of material production and basic manufacturing, it is necessary to impart a known twist contour to a long slender member. Also, in the production of aluminum extrusions, there is typically a high premium on straightness of the product, including “twist straightness.” The current method for the latter is a laborious, trial and error method that greatly limits the speed and accuracy of the process, and inevitably leads to conservative or wasteful design practice. This paper presents a method for placing the process of longitudinal twist deformation under real-time, closed-loop control so as to eliminate the inaccurate and costly iterative processes now used. The basic approach involves measuring the elastic springback in-process using appropriate torque and rate of twist measurements. Given these measurements in real time, a closed-loop twist servo can be constructed. The relevant mechanics of the process will be presented, and several scenarios for control of the twist process will be discussed. In particular, a method that applies the twist over a “long” length of material, but measures the relative twist over a very short distance, has been studied in detail. This control method has been investigated in a series of experiments using a computer controlled, closed-loop twisting machine constucted for this purpose.