外文翻譯---一種節(jié)能的液壓疲勞試驗機

1、An Electric-power-saving Hydraulic Fatigue-testing Machine Mechanical hydraulic-pulsator machine with three control loops has been constructed. Stability of control is 0.5 percent of the range. Consumption of electric

2、power is about one third of electro-hydraulic machine by A. Ohta and E. Sasaki ABSTRACT An hydraulic fatigue-testing machine combin- ing a mechanical hydraulic pulsator and a closed-loop control system has been const

3、ructed as a trial. The dynamic capaci- ties for load and stroke ranges are 1 MN superposed by a mean load ranging from 0 to 1 MN and 5 ram, respectively, over a frequency range from 3.3 to 10 Hz. The consumption of e

4、lectric power and tooting water for this machine is about one third of the servo-controlled electro-hydraulic machine. The stability of this control system is 0.5 percent of the range. Some experimental results are pr

5、esented to demon- strate the excellent stability of load during fatigue testing. Introduction Hydraulic and resonant-type fatigue-testing machines are used for high-load fatigue tests.l, 2 The resonant- type machine c

6、an be run with a small amount of electric power; however it cannot be run in a high- damping condition of specimens, or long stroke and high-load fatigue test. The hydraulic-type machines can be run in these conditio

7、ns. Thus, the hydraulic fatigue-testing machines are used for high-load and long-stroke fatigue tests. This type of machine is usually divided into two categories: one is the servo- controlled electro-hydraulic mach

8、ine2; and the other is the mechanical hydraulic pulsator. 1-3 The servo- controlled electro-hydraulic fatigue-testing machine 2 has a closed-loop cont“0! system, and this continu- ously corrects the differer/ce of t

9、he load or elongation signal from the command signal. Therefore, the servo-controlled electro-hydraulic machine can be operated in an arbitrary waveform of the load or elongation under limited-frequency conditions.

10、That is, it can produce not only a sinusoidal waveform but also a random waveform in accordance with a com- mand signal generator. The machine of this type, however, needs large amounts of electric power and water

11、for cooling of oil, so it is expensive both in A. Ohta and E. Sasaki are Researcher and Chief of Fatigue 2nd Laboratory, respectively, Second Fatig~e Laboratory, Fatigue Testing Division, National Research Institute fo

12、r Metals, 2-3-12, Nakameguro, Meguro-ku, Tokyo 153, Japan. Original manuscript submitted: August 15, 1974. Revised version ~e- calved: ]une 24, 1976. construction and in operation. In case a laboratory does not have

13、a sufficiently large electric supply sys- tem, this kind of machine cannot be equipped. On the other hand, the mechanical hydraulic pulsator ma- chine 3 needs less electric power and less water for cooling than the

14、servo-controlled electro-hydraulic machine does. However, this machine has an open- loop control system. That is, once the amplitude value of load has been set at the beginning of the test, this value is not control

15、led automatically. More- over, the mean value of load is kept only within 5 percent of load range by an action of two oil-pressure switches which are connected through the mechani- cal-pulsator unit by means of a rota

16、ry valve con- nected to the working cylinders. This on-off control system cannot maintain the set value at the beginning of the test because of the change in the compliance of the specimen and the change in the tempe

17、rature of the oil. Therefore, an operator has to correct manually the load that changes every minute with the advance of fatigue testing. Further, this machine could only be used for constant-load fatigue tests of s

18、inusoidal wave. Thus, in order to obtain a low consumption of elec- tric power as well as good stability in control, an hydraulic fatigue-testing machine equipped with a mechanical hydraulic pulsator and a closed-lo

19、op con- trol system was constructed as a trial. This paper reports the principle of the system and the excellent performance of this machine. Control System As mentioned above, this machine was constructed based on t

20、he load-generating mechanism of the me- chanical hydraulic pulsator. 1-3 This mechanism gen- erates the alternating load and the mean load inde- pendently. Namely, it consists of two parts: a me- chanical hydraulic p

21、ulsator which has a smaller cross section and a longer stroke than the actuator and generates alternating oil pressure by the reciprocation of a plunger, and a small oil pump that supplies a Experimental Mechanics I 3

22、7 in volume with the elongation or the shrinkage of a specimen, becomes negligibly small and the pressure is regarded to be constant for a short period of time. For the compensation of a decrease in pressure of this

23、cylinder which follows from a leakage of oil with a lapse of time, a servo-valve is actuated by the com- mand of a signal from a servo-amplifier, which is equivalent to the difference of the output signal of a pressu

24、re transducer inserted in the upper cylinder from the value Pc set at the beginning of test in the constant-pressure setting unit. The alternating component of pressure, Pa sin ~t, in the lower cylinder is excited by

25、 a mechanical hy- draulic pulsator. This is composed of a pulsator cylinder on a rocking-arm which rocks with a rota- tion of a crankshaft. The pulsator ram bobs up and down with the movement of the rocking arm, mak

26、es the volume of cylinder alter, and excites the alter- nation of oil pressure. The alternating oil pressure excited in this manner reaches the lower cylinder through the pipeline and applies the alternating load to

27、 the specimen. The amplitude of this alternating oil pressure, Pa, is determined by the position of the plunger on the rocking arm. The closer the position takes to the fulcrum of the rocking arm, the smaller the amp

28、litude becomes. Thus, when Pa has to vary, the pulsator cylinder is moved on the rocking arm by the run of a servo-motor. The value of amplitude detected through peak detecting circuits is compared with the value whi

29、ch has been previously set in an amplitude-value-setting unit at the beginning of test. Then the load amplitude is kept constant by the ac- tion of the servo-motor run by the amplified signal of the difference in thi

30、s comparison. As for the mean-load control, the output signal of the mean value, Pro, is compared with the value that has been previously set in a mean-value-setting unit. The servo-valve supplies the oil pressure, P

31、t, in the lower cylinder which corresponds to the difference signal in this comparison only of the mean value. Flow rates of the servo-valves that are used for the control of mean load, Pro, and of constant pressure,

32、 Pc, are very small as compared with that of the servo-valve which is used for the usual servo-con- trolled electro-hydraulic machine and continuously corrects the difference of the load or elongation signal from the

33、 command signal of a sinusoidal waveform or a random waveform. As mentioned above, this machine has three control loops: for constant pressure, amplitude value and mean value. Each control circuit has a proper inte-

34、 grating circuit to avoid the interference between each other. So far, the control system was explained as for the load control. An elongation control can be conducted by interchanging a load cell with an extensomete

35、r. When a program test is required, the amplitude and mean-value-setting units could be replaced by suit- able programmed signal generators. Peak-detecting Circuit The peak-detecting circuit is shown in Fig. 3. An i

36、nput signal branches off in two: one is used for the detection of the upper peak, and the other, the lower peak. The upper-peak value is detected as follows. Diode D1 allows current to flow only in one direction to c

37、harge a holding capacitor C1 - D2 provides feed- back for A1 after a peak is detected. And C1 holds the upper-peak value of the signal. 4 In this situation, when the upper peak of the signal becomes small, the d-c v

38、oltage does not follow it. So, to reset this value, an FET switch SWl is closed by a synchronized pulse eT1 from the mechanical hydraulic pulsator. Then eupl value is reset to --~Yrnax at each cycle. Before cup1 is r

39、eset, this voltage has been transmitted to the holding capacitor C2 by a synchronized pulse er2. Thus, the upper-peak value responses with a de]ay of a quarter cycle. Now, the lower-peak value is detected in the same

40、 manner as in the upper-peak detector by re- e rl _, er2 - en~ I ,oK .-~ : i ~oK er2 ~OK F J_ e~p IOK elpl -L eLp J~ lOOK lOOK 50 K 1 ( 3 0K 50 K ~ OK 2~ eamp= eup ~ ~p emea.n = eup ~ etp 2 Fig. 3--Peak