CA1077302A - Earthquake simulator - Google Patents

Abstract

EARTHQUAKE SIMULATOR

Abstract An earthquake simulating machine has a vibrating plat-form mounted in a frame. The platform is driven by a hy-draulic piston which reciprocates the platform through a lever system having a mechanical advantage of about ten to one.
The vibration of the platform is isolated from the frame by shock absorbing bushings which support the lever system.
Shock absorbing feet may be used to support the frame. The hydraulic piston is controlled by a hydraulic circuit and by an electrical circuit which provides the input to the hydraulic circuit. A feedback circuit monitors the output vibration of the platform

Description

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Background and Summar ~ e Invention While almost everyone has experienced an earthquake ~ 15 of moderate strength, which~rattles cups and saucers, very i few people have been subjected to an earthquake comparable to

2 ~ the great San Prancisco earthquake which occurred around the turn of the century and caused considerable damage. Having not experienced a large earthquake, most people would be lnterested in experiencing a demonstration which would resemble as closely as pocsible the real quake wit~out the attendant danger. ~pplicants have succeeded in inventing a vibrating platform machine which will provide the trembling earth sensation required for such an earthquake simulation. When video and audio presentations accompany this trembling earth sensation, and ~he demonstration ;~ is conducted in a closed booth, a very realistic eEfect i5 created ~` ~or the person in the booth.
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It can be appreciated that thcre are several major problems tha-t applican~ had to overcome with theix desicJn tha-t are inherent in such a rnachine.
Perhaps the hardest problem to solve is elimina-ting the transmission of vibra-tion from the earthqu~ke machine to the containing building. Any building which is subjcct to repeated vibration over an extended period of time will develop structural problems which it might not otherwise develop.
If a design depends on anchoring the machine to bedrock to overcome this problem, the installation becomes very expensi.ve and for all practical purposes is limited to ground floor in-stallations. Applicants' design requires no special installa-tion or mounting and is not restricted to use on the ground floor. Applicants' apparatus provides a vibrating surface while transmitting only a greatly attenuated vibration through its frame to the floor.
; Another problem inherent in an earthquake machine is the danger of injuring people by providing too "hard" a shock r during a demonstra-tion,which would possibly damage cartilage o~ the ankle or knee or injure the spine. A "hard" shock is produced in designs which too rapidly accelerate the person experiencing the vibrations produced. Applicants' design prevents against this by producing "soft" shocks.
Injury could also be caused by some designs if the control fails, causing the main driving means to drive the vibrating platform beyond its normal amplitude. This could seriously injure anyone experiencing the demonstration as well - as possibly damaging the machine. ApplicantS' design avoids this possibility.

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In accordance with this inven-tion there is provided a device to vibrate a surface having a frame and means in the frame mounting a plate, the mounting means including a first resilient mount connected to the plate and to a driving lever, the driving lever being connected at one end to a second resilienk mount and the second resilient mount being connected to a damping support connected to the frame. The driving lever is connected at a second end to a driving piston, the piston having a power cylinder capable of reciprocating the piston at a preselected frequency and thereby oscillating the driving lever to oscillate the plate through the first resilient mount. The first and second resilient mounts are positioned to reduce the amplitude of the oscillations of the plate relative to the oscillations of the reciprocating piston. The power cylinder is mounted on a shock absorbing plate having a plurality of layers, at least two of the layers having different vibrational modes, the plate being mounted in the frame. Valve means adapted to control a power source, are connected to the power cylinder to actuate the cylinder at a preselected frequency in response to an input signal. Means are provided for increasing the response sensi-tivity of the power cylinder, and a feedback cylinder is connec-ted to the plate to generate a positional feedback signal for comparison with an input signal. The frame has shock absorbing means to absorb vibration transmitted to it.
A preferred embodiment of the invention will now be described with reference to the accompanying drawings.

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Description oE the Dr~ ings _ _ Figure 1 is an overall view of the machine.
Figure 2 is a sicle vi~w, as viewed from the lony side.
Figure 3 is a side view as viewed from the short side.
Figure 4 is a cutaway top view as taken along lines 4-4 of Figure 2.
Figure 5 is a cu-taway short side view as taken along lines 5-5 of Figure 4.
lC Figure 6 is a detailed view o~ the collar and hinge pin assembly taken along lines 6-6 of Figure 5.
Figure 7 is a schematic o~ the signal generating and feedback circuit.
~ Figure S is a schematic of the hydraulic circuit.
Figure 9 is a partial sectional view of the sandwich plate~
Description of the Preferred Embodiment Applicants' design incorporates a hydraulic drive/power - system (Figure 8) which is controlled by an electrical system to vibrate a plat~orm. Eydraullc, electric and pneumatic systems could be used interchangeably to provide the drive power or control for the machine without deviating from the concepts of the invention.
The hydraulic drive system has a source of hydraulic 25 - fluid under pressure, an intexface oircuit to regulate pressure r an electrically controlled hydraulic valve, and a main drlve piston.
An electrical (Figure 7) system is used to control the hydraulic drive system. The electrical system has an input 10>~'~3~

d~vic~ Eor readiny in t-ne alnp:Litude and :Erequency oi the de-sired shock pattern, a platform Eeeclback posltion, an electronic logic control which evalua-tes the inpu~ and feed-back signals and generates -the signal which operates the ~Iydraulic valve, and an optional D.C. power supply for the elec-tronic logic control.
The mechanical structure of the machine (Figure 13 has a tubular frame with shock absorbing machine feet and a steel plate on which is mounted a multiple layer, shock absorbing sandwich sub-plate. This sandwich sub-plate has layers of materials with di-Eferent vibrational qualities which reduces the amount of shock transmitted to the frame.
Brackets extending upward from the frame provide the mounting~
points for the driving arms which in turn provide the mountiny points for the pla-tform. Between the brackets and the driving arms, and between the driving arms and the platform are ~ spacers which absorb and dampen the vibration generated by the ; driving arms.
By slightly binding the platform mounting, a snaking 20- effect or sideways motion may also be achieved when the plat-form is vibrated. ~his is desirable,as a snaking effect is sometimes evident in a real earthquake. A snaking effect could be achieved by providing another drive system and another channel of the present control system~ This latter method would be more expensive, but would provide additional means of controlling the magni-tude of the effect.
The platform mounting points are offset inboard of the driving arm mounting poin-ts (Figure 2). This offset en-.

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3~2 - ables the clrivincJ arms to work with a lever ac-tiorl in driy;i,ncJ
plat:Eor.m, w:i.th the dr:ivincJ arm Tnounting po:int acting as the fulcrum. This great:ly reduces the deElection a-t -the bracXet for ~ny desired plat~orm deflection tusually about fifty microns.) The shock and vibration transmitted to the ~rame is directly related to the vertical deflection -transmi-tted by the mounting bràcket. The lever action design coupled with the shock absorbing spacers are extremely effective in great-ly reducing the vibration transmitted by the bracket to theframe. The deflection measured by a seismograph placed on . the platform while simulatlng an earthquake intensity of 6 : on the MercalliScale is approximately fifty times that measured by the same seismograph when placed on the tubular frame. The attenuated vibration induced in the frame is isolated from the floor by the use of shock absorbing machine feet. These feet.
are of the conventlonal type used to isolate large machines which tend to vibrate and transmit vibration.

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As shown in Figure 1, the earthquake simulator 20 has a tubular metal frame 22 having four shock cushioning machlne ,, feet 24 attached by bolts 26 at the corners. A metal plate.28 is bolted with bolts 30 to the center of the frame 22 and is us~d for mounting the sandwich plate 32. The sandwich plate 32 is made up of a plate of Delrin (TM) 34.or any other similar plastic between two metai plates 36 and 38, which are bolted tog~ther with bolts 39 and mounted on the metal plate 28.
This sandwich plate 32 reduces the transmission of shock and vibration from the main drive piston 4~ mounted thereon to ~7t7~02 the frame 22 bec~use oE the cli~f~rent vibratiQnal modes of the ma-terial compr.ising the sandwich p:late 32 and the decoupling ef:Eect of using separate bolts 39 to fas-ten the plastic plate 34 to each o:E the metal plates 36 and 38 as shown in Figu~e 9.
The sandwich plate 32 is stud mounted to the metal plate 28 with four stud and nut assemblies 42, as shown in Figure 1. These stud and nut assemblies 42 are adjustable to allow for proper leveling of the main drive piston 40 in re].ation to the driving arms 44, as shown i.n Figure 2.
Four brackets 46 are bolted to the frame 22 and extend upward to provide the mounting points for the driving arms 44. These brackets 46 are preferably flexlble to lS partially absorb the shock and vibration induced by the driving arms 44; ordinary st~el strap has been found to have sufficient flexibility, but other materials could be used.
- The driving arms 44 are connected to the brackets 46 by bushings 48 and bolts 50 and 51. The platform 52 is -- connected to the driving arms 44 by bushings 54 and bolts 56, 57.
- As can be seen from Figure 5, the mounting bushings 54 for the platEorm 52 are offset inboard of the moun-ting bushings 48 for the driving arms 44. This offset allows the driving arms 44 to work in a lever type action gearing down -- .

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the total travel of the main clrLve piston ~0 ln the r~-tio oE the length of the drivincl arms ~ -to the amount o~ the offse-t. This ratio is appro~imately -ten -to on~ in the preferred embodiment of applicants' device but o-ther ratios coulcl be used to provide different ope~a-ting charac-teristics.
If -the control mal~unctions and drive p:iston 40 is driven to its maximum extension, the gearing down will maintain the increased amplitude in the same order as the desired vibration. The machine would not be damaged. Bushings 48 and 54 are rubber bumper shock spacers which cushion and dampen the vibration of the platform 52 as well as providing the elastic pivot points for levers 44.
The main drive pis-ton 40 is mounted on the sandwich plate 32 and connects to the driving arms 44 by means of a collar 60, as shown in Figure 6. Collar 60 is threaded onto the shaft 61 of the main drive piston 40 and fixed by lock nut 62, as shown in Figure 5. Collar 60 has freely rotatable pins 64 which fit through holes 66 in -the driving arms 44.
The pins 64 allow ~he collar 60 to move up and down at a fast rate without bending arms 44 or developing excess heat ~ due to friction.
The simulator 20 is powered by the compressor 67 which operates drive piston 40. Power to drive piston 40 is controlled by control valve 68~ The action of the compressor 67 t valve 68 and piston 40 is regulated by the pressure regu:Latin~ circuit 69. Piston 40 is preferably a ~C~'773~

do~lble act:incJ hydraulic p:iston. ~ double acting hydraulic piston model r~ulsxlDK obtained Erom She~Eer Corporation has been found to operclte satisEactorily a~ pis~on 40. Control valve 68 is preferably a East acting servo valve. ~ servo valve model DSV~fS-600-S obtained Erom Parker ~IanniEin has been found to operate satisEactorily as con-trol valve 68.
In the preferred embodimen-t, the pressure requlating circuit 69 has a pressure accumulator 70, an on-off solenoid valve 72 and a pressure gauge 74. The accumul.ator 70 prevents sudden losses in hydraulic pressure being applied to the piston 40 as it responds to the command - variations of servo valve 6B. The pressure gauge 74 is used to monitor the hydraulic pressure during operation.
The hydraulic pressure is normally 350 p.s.i. Also shown : 15 are bleeder lines 76, 77 which are "teed" into a single return line 78 by a Tee connection 80. These are used when first setting up the machine to bleed the main drive piston 40. Needle valves 81, 82 are included in each bleeder line 76, 77 for "dithering" the servo valve system and thereby improving the performance characteristics of the - simulator 20. "Dithering" is accomplished by adjusting the needle valves 81, 82 to a constant level of pressure drop so that the double action drive piston 40 is in an agitated condition and thusly more sensitive to a change in input pressure supplied by control valve 68. This reduces the response time of the drive piston 40 as the pressure 8.

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b~l:i.ldup rate is constant ~or clny pclrticulclr control v~lv~ 68, but the requ:ire~ input pressure to trigger the drive piston 40 is reduced from the non-ditherillcJ level, hence reducing the time delay from the control valve 68 initiating a move command to -the -triggerillc3 of. the drive piston ~0.
"Dithering" also increases the accuracy capabilities of the simula-tor 20 in following any input vibration pattern as the overall system sensitivity oE the simulator 20 is increased.
A more sophisticated "dithering" can be applied to the drive piston 40 by using a valve arrangement to respond to changes of pressure which would further decrease the overall system Fesponse time. This sophisticated "dithering"
would be useful in scientific applications requiring a much more accurate reproduction of the desired vibration pattern.
"Dithering" could also be used in an electrically operated simulator 20 where tne drive piston 40 would react to voltage levels by applying a float voltage to the drive piston 4n.
Similarly, a pneumatic control system could be "dithexed"
to enhance simulator 20 performance.
A regulated supply of pressurized hydraulic fluid from regulating circuit 69 is used to operate the main power piston 40 by the fast acting servo control valve 68.
.When it is desired to raise the platform, the con-trol valve 68 receives an "up" signal from the electronic control 84 which causes the control valve 68 to open the line of 73~, pressuri~ed fluid to the "up" cy:Linder of piston ~0. This causes the shaft of the piston ~() to extend, thereby raising the platEorm. When it is desired to lower -the platform, the con-trol valve 68 receives a "down" signal from the electronic control 84 which closes the line of fluid to the "up" cylinder and opens the line o~ fluid to the "down" cylinder oE the piston 40, thereby driving the platform downward.
By mounting the platform 52 in a slight bind, a slight sideways motion or snaking effect is produced as well as the up and down motion when the platform 52 is operated.
This is desirable as a slight ~aking effect can be felt in most earthquakes. A separate driving means could also be used to drive in the horizontal plane. Control of the 1~ snaking effect prod-tced by the separate drive means could be added by using another channel in the input signal or by multiplexing and decoding in the same channel. Feedback could be provided by a piston similar -to that presen-tly used for the up and down motion. By controlling -the snaking effect, a more accurate representation of an earthquake could be produced for precise scientific applications of the machine. This increased control over the snaklng effect, however, is not normally noticeable to people experiencing an earthquake demonstration.
The acceleration of the platform in its excursion up and down is controlled by the use of a single main drive piston 40 and the hydraulic control system 69. The 10 .
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accelera tion coulcl also be mclde varlable by adding more control valves similar to valve 68, by USin~J a multi-orifice control valve, or by providing for means -to ~xhaust the fluid from the oppos;ng side oE the main power pis-ton 40 while supplying the fluid -to the driving cylinder. By varying the acceleration, subtle niceties (desirable in scientific applications) could be added to enhance the already realistic effect possible with the preEerred - emboaiment.
The electronic logic 84 is depicted ln ~igure 7 and is one of many such circuits -that could be employed in the invention. The various electronic components which are used can be purchased commercially from any electronic parts suppliex. ~pplicants have chosen to use National Semi-Conductor and Fairchild Mfg. Company components and the part numbers used are of those manufacturers.
The input signal is generated by a tape reade~, a signal generator, or any other source 86 which could -- :
supply the waveform of the vibration to be reproduced by the machine. This input signal is fed into an active filter 88, (National Semi-Conductor p/n LM310) which eliminates any signals of a frequency higher than 10 hz. from the ; input. Thls output i5 then conditioned and amplified by a signal conditioner 90, (Nat. Semi-Conductor p~n Lkl741) before being fed into a comparator 92 (Nat. Semi-Conductor p/n LM741). The comparator 92 compares this input signal 11 .

10773~2 with the signal yener~ted by the platform feedback sensing element 94, which is directly proportional to the position of the platform 52, and produces a signal which is proportional to the difference between the desired position and the actual position of the platform 52. The output of the comparator 92 is amplified by a power amplifier 96 (Fairchila p/n 791) and supplied to the control valve 68 to bring the actual position of the platform 52 to the desired position. The electronic control logic 84 is thereby continuallyrcomparing and correcting the actuaL
position of the platform 52 with the desired position which ensures an accurate reproduction of the desired waveform.
A simple toggle switch (not shown) similar to a light switch is mounted in the electronic control box 84 -and is used to turn the power off and on.
~ Also not shown is an optional 28 V.D.C. power supply which converts llOV. A-C to supply power for the logic control circuitry, if 28 V.D.C. is not otherwise avaiLable.
It can be appreciated by one skilled in the art that there are many modifications which could be made to the specific form or arrangement of parts herein described without departing from the concept of the invention. -,

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A device to vibrate a surface having a frame, means in the frame mounting a plate, the mounting means including a first resilient mount connected to the plate, the resilient mount being connected to a driving lever, the driving lever being connected at one end to a second resilient mount and the second resilient mount being connected to a damping support connected to the frame, the driving lever being con-nected at a second end to a driving piston, the piston having a power cylinder capable of reciprocating the piston at a pre-selected frequency and thereby oscillating the driving lever to thereby oscillate the plate through the first resilient mount, the first and second resilient mounts being positioned to reduce the amplitude of the oscillations of the plate re-lative to the oscillations of the reciprocating piston, the power cylinder being mounted on a shock absorbing plate hav-ing a plurality of layers, at least two of the layers having different vibrational modes, the plate being mounted in the frame, valve means adapted to control a power source, the valve being connected to the power cylinder to actuate the cylinder at a preselected frequency in response to an input signal, means increasing the response sensitivity of the power cylinder, and a feedback cylinder connected to the plate to generate a positional feedback signal for comparison with an input signal, the frame having shock absorbing means to absorb vibration transmitted to the frame.