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1、A Closed Loop Feedback Method for a Manual BarStraightenerRobert J. Miklosovic, Zhiqiang GaoDepartment of Electrical and Computer EngineeringCleveland State UniversityCleveland, Ohio, USAAbstractAutomation of a unique manually controlled industrial bar straightener is proposed. A continuous-time clo
2、sed loop model is constructed in Simulink for an event-driven process through the use of asynchronous timers. The system is simulated with linear and nonlinear PD controllers. A nonlinear filter,called the tracking differentiator, is introduced as an alternative to a linear approximate means of prov
3、iding accurate derivative feedback in the presence of noise. In both cases, the nonlinear techniques outperformed their linear counterparts while retaining tuning simplicity.I. BACKGROUNDPrecision straightening of a cylindrical metal bar is largely based on the ability to precisely measure its geome
4、try. A few fundamental measurements and how each influences the tolerance specification on straightness should first be understood. Methods for measuring roundness and straightness are covered to lay the groundwork for the problem formulation. The basic operation of the machine is outlined in Sectio
5、n II, and its fundamental limitations and need for automation are discussed. Section III addresses the task of closing the loop through block diagrams and the role of new hardware in the process. Section IV contains descriptions of all of the blocks that are modeled in Simulink. The linear and nonli
6、near controller designs are discussed in Section V, the system is simulated in Section VI, and concluding remarks are made in Section VII.A. Measuring RoundnessRoundness is a quantity derived from comparing the shape of a cross-sectional area at one distinct point along a cylinders length against a
7、circle. A round metal bar that is arbitrarily long with respect to its diameter has to be checked for roundness in many locations lengthwise and averaged to insure overall consistency. Roundness is approximated by rotating the work piece one revolution in a Vee block while measuring the surface with
8、 an indicator. Taking the difference between the minimum and maximum indicator readings in this case is referred to as the total indicator reading (TIR) 1.B. Measuring StraightnessStraightness is a quantity derived from comparing the axial centerline of a specific section of a cylinders length again
9、st a straight line. A simple method for approximating straightness is by rotating the bar one revolution between two Vee blocks that are a fixed distance (d) apart, while measuring in the center with an indicator. The distance that the axial centerline of the part deviates from a theoretically strai
10、ght centerline directly below the indicator equals the extent to which the part is bowed, or warped, over length d. The maximum and minimum indicator readings (IX and IN) are physically represented in Fig.1. From this, TIR is derived as:TIR= IX IN = (R + |Bow|)-(R |Bow|) =2*|Bow| (1)Deviations in ro
11、undness, outside diameter (OD) size, and finish can adversely affect the measurement.Figure 1. Max. and min. indicator readings of a bowed partC. StraighteningThe straightening process, which can be broken into steps, simply involves correcting any error while checking for straightness. First, the p
12、art is measured for straightness. Then, it is rotated so that the bow is oriented 180 degrees away from the Vee blocks with the maximum indicator reading facing upwards. Finally, a counter-bending force replaces the indicator and straightens the work piece against the Vee blocks.II. MACHINE OPERATIO
13、NThe straightener to be automated uses a non-contact ultrasonic sensor in place of the indicator and rollers in place of the Vee blocks in an effort to minimize contact wear. The part slowly spirals through the machine. The indicator reading becomes a continuous sinusoid at the sensors output, havin
14、g a peak-to-peak value equal to the TIR each revolution. TIR is sampled from the sensor output and calculated each revolution, making the sample period of one revolution the minimum time between consecutive bends (YSP). TIR is the plant output (Y) to be controlled. When the part is straightened, the
15、 machine stops rotation with the bow facing upwards, but the part continues to feed lengthwise while an air cylinder counterbends the part over a period of time. This bend time (BT) is the control variable (U). Fig. 2 illustrates this operation.Figure 2. The straightener to be automatedA. Process Li
16、mitationsThere are aspects of the process that can limit the controllers performance and slow it down by extending YSP. Each is observed and taken into consideration when producingan accurate simulation model:1. The ultrasonic sensor introduces RFI noise into its. The use of a feedback filter is essential.2. A rough part surface finish adds distortion to the sensor output.3. An out-of-round part superimposes harmonics on the s
