Abstract:
A servo-control circuit for use in an electro-hydraulic system capable of mulating dynamic conditions for a controlled load vs. time history.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention. 
     The present invention relates generally to servo-control circuits and, more particularly, to such circuits for use in electrohydraulic systems capable of simulating dynamic conditions for a controlled load vs. time history. 
     2. Description of the Prior Art. 
     A need has existed for some time for a system to simulate the dynamic effects on aircraft members during a typical catapult launch from an aircraft carrier. Such a system would enable scientists and engineers to experiment with such aircraft in a laboratory environment under controlled conditions. The present invention fills this long felt need. 
     SUMMARY OF THE INVENTION 
     The present invention provides a circuit for driving a servo-amplifier which in turn drives a mechanical linkage mechanism attached to an aircraft member. The circuit electronically simulates a controlled load vs. time history for an aircraft holdback fitting fracture when the required catapult load is reached. 
     Accordingly, one object of the present invention is to simulate a controlled load vs. time history. 
     Another object of the present invention is to simulate the dynamic effects on an aircraft member during a typical catapult launch. 
     Another object of the present invention is to reduce response time. 
     One other object of the present invention is to decrease expense and increase reliability. 
     Other objects and a more complete appreciation of the present invention and its many attendant advantages will develop as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a schematic diagram of a specific embodiment of the present invention. 
     FIG. 2 illustrates a plurality of signals generated by the circuit of FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning to FIG. 1 where simulator circuit 10 is illustrated, a one Hertz clock-pulse generator 12 is connected to a three-bit binary counter 14 via line 16. Three bit binary counter 14 is connected to NAND gate 18 via lines 20, 22, and 24. The driver signal output from NAND gate 18 on line 26 is illustrated in FIG. 2b while the clock signal on line 16 is illustrated in FIG. 2a. It is noted that the driver signal on line 26 is a seven second pulse of amplitude A followed by a one second zero voltage level. 
     The driver signal on line 26 is connected to summing signal generator 28 via line 30. Summing signal generator 28 includes inverter 32, inverter 34, potentiometer 36, integrator 38, limiter 40 and integrator reset circuit 42 as well as interconnection lines 44, 46, 48, 50, 52, 54, 56, 58 and 60. Line 62 comprises the output of summing signal generator 28 upon which the summing signal illustrated in FIG. 2(f) appears. It is noted that the first seven seconds of the signal on line 30 (FIG. 2b) causes integrator 38 to develop a ramp output signal on line 60. The slope of the ramp output signal on line 60 may be adjusted by varying potentiometer 36. Limiter 40 is preset to limit the output on line 62 to a specific d-c voltage level. Thus, as illustrated in FIG. 2f potentiometer 36 adjusts the slope of the ramp signal output on line 60 so that the ramp signal reaches the specific d-c voltage level set by limiter 40 after four seconds. Then the output is limited on line 62 to the specific d-c voltage level set by limiter 40. The trailing edge of the seven second pulse of the driver signal on line 30 (FIG. 2b) causes integrator reset circuit 42 to reset integrator 38 back to a zero voltage. This is also illustrated in FIG. 2f. 
     The trailing edge of the seven second pulse of the driver signal on line 64 (FIG. 2b) also fires monostable multivibrator 66 for a time period of 120 milliseconds. The output of monostable multivibrator 66 appears on line 68 and is illustrated in FIG. 2c. 
     The driver signal on line 68 (FIG. 2c) inputs monostable multivibrator 70 via line 72. The trailing edge of the driver signal on line 68 (FIG. 2c) fires monostable multivibrator 70 for a time period of 500 milliseconds. This five hundred millisecond pulse is inverted by inverter 74 and appears as a summing signal on line 76. This summing signal appearing on line 76 is illustrated in FIG. 2e. Monostable multivibrator 70 is connected to inverter 74 via line 78. 
     The driver signal on line 68 also inputs pulse shaper filter 80 via line 82. Pulse shaper filter shapes the 120 millisecond square pulse on line 68 into a spike or steep ramp function pulse. This spike pulse appears on line 84. Line 84 inputs potentiometer 86 which may be utilized to adjust the spike pulse level. The level adjusted spike pulse appears as a summing signal on line 88 and is illustrated in FIG. 2d. 
     Potentiometer 92 may be utilized as a d-c voltage offset adjustment. The output of potentiometer 92 appears on line 94 as a summing signal. 
     Summing junction 90 sums the summing signals appearing on lines 76, 62, 88, and 94 with the sum appearing on line 96 which inputs output amplifier 98. Output amplifier 98 outputs a servo-driver signal on line 100 which is illustrated in FIG. 2g. The signal on line 100 drives a servo-amplifier (not shown) which in turn actuates a mechanical linkage that is attached to an aircraft member. 
     The signal illustrated in FIG. 2g is utilized to simulate the dynamic effect on the aft fuselage structure of an A4 aircraft during a typical catapult launch. In particular, to simulate the holdback fitting fracture which occurs when the required catapult load is reached. 
     FIG. 2g illustrates the load vs. time history for the holdback fitting fracture. First, a slow four second ramp to 12,500 pounds is developed. Then, a holding time of three seconds follows terminated by a 120 millisecond pulse to reach the nominal breakaway failing load of 28,500 pounds. The final event is to simulate the actual breaking of the fitting by commanding an instantaneous zero load. This is accomplished by actually developing a negative load. This negative load is not actually felt by the aircraft member since the mechanical linkage will not support a compression load. The signal in FIG. 2g develops a high negative load to give the servo amplifier a large negative error signal. 
     It is noted that the clock pulse signal illustrated in FIG. 2a is a one Hertz signal. However, for different applications different frequencies may be utilized. Also, the time periods associated with monostable multivibrators 66 and 70 are mere matters of design choice. Such time periods may vary for other applications. 
     From an inspection of FIG. 2, it is noted that for every eight cycles of the clock pulse signal (FIG. 2a) the servo driver signal (FIG. 2g) is repeated. 
     It will be appreciated by those skilled in the art that the complete circuit diagram of FIG. 1 includes such suitable and necessary biasing voltage sources as are usually provided in simulator circuits. Such biasing is not shown in FIG. 1. 
     Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described herein.