机械外文翻译调直机的反馈方法.docx

1、机械外文翻译调直机的反馈方法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 conti

2、nuous-time closed 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

3、 means of providing 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 mea

4、sure its geometry. 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 outl

5、ined in Section 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 li

6、near and nonlinear 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 len

7、gth against a 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 th

8、e surface with 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 cylinder

9、s length against 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 theor

10、etically straight 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)De

11、viations in roundness, 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

12、. First, the part 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. MA

13、CHINE OPERATIONThe 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

14、 output, having 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 str

15、aightened, the 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 automate

16、dA. Process LimitationsThere 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

17、 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 sensor output sinusoid, placing a bound on the minimum steady state error that is achievable.4. Inconsistent material density produces false measurements. Th

18、e measured focal length of atransducer is dependent on the density of the material that is being measured 2. The unit cannot measure accurately in the presence of a time-variant material density (i.e. hard spots). Although unavoidable, it can be detected, since TIR changes monotonically.5. An incons

19、istent OD causes vertical shifts in the sensor output. A differential TIR measurement cancels these affects.6. A twisted part condition is detected when the angular position of the maximum indicator reading slowly moves with each revolution. This condition is created when the part is not straightene

20、d at the precise angular location and occurs because of the quantization affect of the digital readout used by the operator. The new controller will use a continuous signal and the part can be straightened 30 to 45 degrees ahead of the twist when encountered.B. The Need for AutomationReplacement of

21、the operator with electronic hardware is beneficial in several ways. The cost of the electronics is much less than the ongoing hourly wage and schedule of an operator. The limitations associated with the digital readout are eliminated, which helps the machine to straighten faster with more precision

22、. The process can be drastically sped up to produce more. Though the minimum sample time is one revolution, it does not need to be slow enough for human comprehension. A Programmable Logic Controller (PLC) can make several calculations and test the result against a set of rules many times faster tha

23、n a human being.C. Research MethodologyThe focus is split between modeling and control design, since this is a new control problem. The process is manually controlled rather than being strictly manual in operation, meaning the machine needs only a new controller. There is no need for a complete mech

24、anical overhaul, so the best method of straightening is not researched. Typical of a small company, time and money are limited. Gao and Huang 3 presented a new error-based control design framework including such innovations as a nonlinear tracking differentiator and a nonlinear proportional-integral

25、-derivative (NPID) control method. These methods prove to be powerful and simple to tune, which make them ideal for use in an industrial environment.III. A CLOSED LOOP SOLUTIONThe task of automation can begin once the process is well defined. A straightforward system block diagram is developed, and

26、each block is modeled in Simulink. Aspects of the hardware configuration are carefully considered.A. From Open Loop to Closed LoopThe open loop multi-input-multi-output (MIMO) block diagram, in Fig. 3, represents the manually controlled process. The operator calculates TIR and monitors the angular p

27、osition (􀀀 P) of the bow with each revolution. When Y approaches a specified limit, the operator sets BT proportional to Y and itsrate, and then pushes a button (BP) to straighten the part. The bend timer creates a pulse triggered by BP that counter-bends the part for BT minutes. This event

28、 forces the part to have a specific rate for a period of time. After the event, the part takes on a new rate and the process perpetuates. Therefore, Y is apiece-wise continuous function of time. The operators involvement in the process is represented as a block in Fig. 4.Figure 3. Open loop block di

29、agramFigure 4. Operator blockRearranging the blocks and breaking each function down into smaller more-manageable blocks reduces the representation to a usable closed loop, single-input-singleoutput (SISO) form. Fig. 5 shows how a SISO plant is obtained by combining the process with the task of sampl

30、ing the TIR, since it can be consistently computed.Figure 5. SISO plant blockThe plant has a variable-width pulse as the input (U) and the sampled TIR (Y) as the output to be controlled. The incoming changing position of the work piece is modeled as an unknown rate disturbance (D). The closed loop S

31、ISO block diagram is shown in Fig. 6.Figure 6. Closed loop block diagramB. Hardware ConfigurationDepicted in Fig. 7, an encoder and a PLC are the only hardware needed for automation. The encoder feeds the angular position of the part back to the controller, and the PLC handles all of closed loop fun

32、ctions outside of the process.Figure 7. Hardware configurationFig. 8 depicts the hardware layout for plant data acquisition during manual operation. The PLC is also used to calibrate a strip chart recorder, shown in Fig. 9, which simplifies calibration for the operator and removes room for error during data acquisition. Using the PLC for both data acquisition andcontrol keeps costs lower.Figure 8. Open loop data acquisition configurationFigure 9. Chart recorder settings for a .006” TIR signalIV. MODELINGSimulation modeling involves the construction of Si