Abstract: A watchcase coupling structure including an outer rim and coupling pins adapted to couple a front cap and a rear cap, wherein the coupling pins may be mounted in the outer rim and the rear cap without relying upon a threading-in method. Each of these coupling pins may take various configurations. Specifically, it may be the one which has an eccentricity by an amount corresponding to a margin required to adjust the force with which the packing interposed between the front cap and the rear cap is clamped or the one which is provided on its head with a slant portion to facilitate the operation of mounting. Furthermore, it may be the one which is provided on the front end with a notch or the like or the one which has a flange to prevent the pin from falling off.

Abstract: An hour meter on a tractor for registering the operating time of the tractor connected for receiving a tachometer signal to energize the hour meter circuit and thereby register the time of engine operation of the vehicle responsive to actual operating time of the engine.

Abstract: In a hinged bracelet formed of a plurality of links arranged in several juxtapositioned, longitudinally extending rows, each link is formed of two link parts bonded to one another along a parting plane. Each link has two throughgoing bores extending transversely to the longitudinal direction of the bracelet and spaced from one another in the longitudinal direction. Each bore is formed by a longitudinally open groove provided in at least one of the link parts. The groove faces with its longitudinal opening, the other link part. Each bore accommodates a hinge pin extending transversely to the longitudinal direction of the bracelet.

Abstract: A construction having holder means for supporting and guiding at least one flexible energy-transferring line. The chain construction being attached at one end thereof to a connecting point and at its other end to an energy-consuming or energy-producing apparatus capable of moving in the longitudinal direction of the line. The holder means comprising line support means arranged to co-act with parallel links, adjacent ones of said links being joined together in a manner such that said links can pivot through a pre-determined angle. Each link is provided with a support surface, said surfaces being mutually arranged to so as to lie in one and the same plane when the holder means are oriented in one and the same plane. At pre-determined links there are provided support wheels, the peripheral surfaces of which wheels extend over adjacent support surfaces.

Abstract: A system for controlling the annular nozzle throat area (and hence the tht) of a solid-propellant rocket by means of a pintle or plug the position of which is caused to vary in response to pressure variations within the combustion chamber of the rocket.

Abstract: A combined cycle power plant includes gas and steam turbines, gas turbine afterburners, steam generators, and a digital/analog control system. A megawatt load control system varies a fuel control signal to govern a detected power output according to a reference value, the fuel control signal determining the flow rate of fuel to a gas turbine. An afterburner is connected to heat the exhaust gas from the gas turbine. Both the gas turbine and the afterburner are adapted to use gas and liquid fuels. During gas turbine fuel transfer, the gas and liquid fuel flows are controlled in response to the fuel control signal to compensate power output disturbances that typically result from various nonlinearities of fuel system elements. Afterburner fuel transfer is initiated upon completion of gas turbine transfer.

Abstract: An exhaust gas purifying device wherein exhaust ports in the respective cylinders of an engine communicate with the respective inflow passages of a thermal reactor, and more secondary air flows into the inflow passage at the part of the thermal reactor with sufficient thermal diffusion than into another inflow passage.Further, a taking-out port for the exhaust gas to be recirculated is provided at the exhaust port which communicates with the inflow passage at the part of the thermal reactor exhibiting insufficient thermal diffusion.

Abstract: An air control valve for directing the flow of air from an internal combustion engine driven pump and including differential pressure actuating means includes a pilot valve responsive to engine induction vacuum level to provide induction vacuum, atmospheric air or air from the pump to the actuating means. The pilot valve includes a chamber having openings communicating with the pump and the actuating means, a restricted orifice to atmosphere, a valve element capable of selectively closing either of the openings, a differential pressure motor actuated by induction vacuum and a tube projecting through the actuating means opening into the chamber, the tube being axially positionable by and in communication with the differential pressure motor to co-act with the valve member and openings to supply high pressure air, atmospheric air or induction vacuum to the actuating means according to the level of induction vacuum.

Abstract: An anti-pollution device for treatment of the gases exhausted from a fuel burning internal combustion engine which comprises a reactor housing through which the exhaust gases are circulated from an inlet to an outlet, means for admixing an oxygen containing gas with the exhaust gases during passage through the housing, means for cooling down the gaseous mixture whereby moisture condenses from the moisture vapor contained in the gaseous mixture to form an alkaline medium from the wet nitrogenous gases and in which surfaces contacted by the gaseous mixture under the conditions described within the housing are formed of a metal containing nickel, cobalt or other metal having a catalytic action to convert pollutants to their more highly oxidized state under the conditions to which the hot gaseous mixture is exposed within the housing.

Abstract: A hydraulic drive system is disclosed. A power wheel or turbine is supplied with motive fluid from a hydraulic pump driven by an appropriate prime mover. The power wheel has oppositely disposed valve plates which alternately register with cavities disposed around the periphery of the wheel to define isolated pressure chambers. A sequencing valve alternately delivers fluid pressure to the pressure chamber in registry with a valve plate. A drive shaft transversely extends from the wheel and is adapted to be coupled to the driving wheels of a vehicle.

Abstract: A fluid drive composed of three coaxial cylindrical members mounted coaxially within a cylindrical housing. The outer of the three coaxial members is fixedly secured to an output shaft and the inner of the three coaxial members is fixedly secured to an input shaft. The intermediate cylindrical member has vanes for fluid interaction with vanes on the inner and outer cylinders.

Abstract: A pair of hydraulic motors are operatively drivingly connected to a common rotatable member and are employed for transmitting power thereto from a pair of prime movers. A first hydraulic circuit communicates with one of the hydraulic motors and includes a pump driven by one of the prime movers while a second hydraulic circuit communicates with the other of the hydraulic motors and includes a fixed displacement pump and a variable displacement pump driven by the other prime mover. A device associated with the variable displacement pump is responsive to fluid pressures in the first and second hydraulic circuits for automatically varying the output displacement of the variable displacement pump so that a predetermined relationship is maintained between the fluid pressures in the first and second hydraulic circuit.

Abstract: The invention discloses a power-steering mechanism for an automotive vehicle, having a double acting actuator with two pressure chambers separated by an actuator piston. The actuator is connected both to the chassis of the vehicle and to a linkage associated with the direction controlling wheels of the vehicle. The pressure in the actuator chambers are controlled by a distributing valve operated by the steering wheel moved in either direction from a central, idle position. A reaction device adapted to create a return force biasing the steering wheel into its central position includes a circular cam eccentrically mounted on the rotating shaft of steering wheel and subjected to a thrust transmitted by a tappet. The tappet is projecting into a closed compartment to engage a reaction piston submitted to the pressure prevailing in a fluid accumulator. Two plungers are slidably mounted in the compartment and are submitted to the pressure prevailing in the actuator chambers.

Abstract: A fluid pressure amplifier for intensifying fluid pressure, the amplifier comprising a housing including a gas-hydraulic interface piston; a first chamber includes a slave piston mounted for reciprocation therein and for abutting engagement with a work piece. A hydraulic fluid path extends intermediate the interface piston and the first chamber so as to apply hydraulic pressure thereto. A second chamber is disposed in the path intermediate the first chamber and the interface piston and includes a check valve in the path intermediate the second chamber and the first chamber. A third chamber, includes a fluid intensifier piston having a head end and a tail end, the head end being mounted for reciprocation in the third chamber and the tail end being mounted for reciprocation in the second chamber. The head end of the intensifier piston has a larger diameter than the tail end and is exposed to gas pressure while the tail end is exposed, in the second chamber, to hydraulic pressure.

Abstract: An exhaust gas channel system which is arranged in the cylinder head of an internal combustion engine and in the housing of an exhaust gas turbo charger flangedly connected to an exhaust flange disposed along the side of the cylinder head; the exhaust apertures of each cylinder are thereby each arranged in that half portion of the respective cylinder which is disposed nearest the cross center plane of the cylinder head while the exhaust gas channels are constituted exclusively by cast-in walls of the cylinder head, on the one hand, and of the exhaust gas turbo-charger, on the other; the latter is threadably connected to the exhaust flange of the cylinder head by means of a complementary counter-flange matched to the exhaust flange of the cylinder head.

Abstract: Waste heat generated by an internal combustion engine is utilized by an apparatus comprising a supercharger, a turbine drivably engaging the supercharger, a vaporizer, and a condenser. The turbine, the vaporizer and the condenser form a closed loop within which a motive fluid is circulated. The vaporizer is intimately associated with the internal combustion engine, and the motive fluid within the vaporizer is converted to gaseous form by heat transfer from the engine. The vaporized fluid is then used to drive the turbine which, in turn, drives the supercharger, thereby increasing the efficiency of the engine. Spent motive fluid is recovered from the turbine, condensed, and recycled to the vaporizer.

Abstract: A protection system is provided for a turbine plant to avoid double shock or similar rotor blade operation. A digital computer controller detects excessive blade loading conditions on the basis of governor valve positions and effects bumpless mode transfer from sequential valve operation to single valve operation to avoid excessive blade loading.

Abstract: A method for controlling stress and increasing the load-bearing strength of support members, the support members comprising coal, of a coal mine wherein the method consists essentially of injecting ammonia or hydrochloric acid into the interior portions of the support members.

Abstract: A modular-like system of offshore structures for imparting flexibility to the offshore exploration and production and transportation industries so that exploration, production and development work can take place over a large range of marine depths and operational circumstances with one or more marine vessels.

Abstract: A ribbed sheet of flowable material is positionable on the sides and roof of an air passage of a mine for sealing irregularities in the sides and roof and extends across the air passage to prevent the flow of air therealong. A plurality of air cells are positioned in closely adjacent relation within the confines of the sheet and are inflatable to block the flow of air through the passage.

Abstract: The device features its housing carrying the soil sampling ing socket and the striker arranged coaxially to said socket, and adapted to act thereupon and establish some chambers in said housing, which are alternatively communicated, through the inlet fitting and the piping connected thereto, with a source of compressed air for the striker to perform forward and return strokes. The piping portion immersed in water is essentially a rigid pipe joined with the inlet fitting by way of an axially spring-loaded sleeve whose one end is rigidly connected to said pipe. Arranged along said pipe is another pipe rigidly coupled thereto and serving for used-up gas to discharge from said chambers to the water surface.Such a device is applicable for soil sampling at depths amounting to several scores of meters.

Abstract: A cable guiding and dispensing chute for use with a ground slitting or trenching implement includes two members releaseably secured together to define a J-shaped box-like structure to guide a plurality of cables which are being dispensed from a drum or reel and being placed in a slot in the ground. One of the cable chute members includes a pair of parallel, J-shaped sidewalls having different widths and being interconnected by a first cable guiding web. The second of the cable chute members is pivotally supported by the J-shaped sidewalls and includes a single sidewall component adjacent to and complementary with the smallest of said J-shaped sidewalls to define a chute wall conforming in size and shape with the largest of said J-shaped sidewalls. A plurality of additional cable guiding webs are connected to the second-member sidewall component and project substantially to the largest J-shaped sidewall to define, with said first web, a plurality of cable guiding conduits.

Abstract: The invention relates to an air conditioning system for producing refrigerated air, comprising as many evaporator convectors as there are rooms to be air-conditioned, each evaporator being connected by means of supply and return pipes, to a condensation unit placed outside the rooms that are to be air-conditioned.

Abstract: A centrifugal refrigeration unit which comprises a rotatable shaft carrying two spiral tubular assemblies, one on each end. Each assembly comprises two spiral tubes. At one end the assembly acts as a condenser, and at the other end as an evaporator. Means are provided for directing separate streams of air across the condenser and evaporator assemblies. Numbering the spirals from the condenser end as first, second, third and fourth, and considering the rotation of the shaft clockwise as seen from the condenser end, the first spiral expands outwardly from the shaft in a counterclockwise direction. The second spiral expands outwardly from the shaft in a clockwise direction. The third expands in a counterclockwise direction, and the fourth expands in a clockwise direction. The shaft is hollow and the small ends of the first and fourth spirals are connected through the hollow shaft.

Abstract: Electronic means for selective raising of the needles in circular knitting machines by the selective raising of jacks individually related to the needles in the cylinder needle slots, the jacks being of the rocking type having a fulcrum butt intermediate their ends. Alternate jacks are mechanically rocked to non-needle raising position while intervening jacks are mechanically rocked to needle raising position. A first electromagnet when selectively energized acts upon the intervening jacks at a point above their fulcrum butts to selectively rock selected ones of such jacks to non-needle raising position, while a second electromagnet when selectively energized acts upon the alternate jacks at a point below their fulcrum butts to selectively rock selected ones of such jacks to needle raising position.

Abstract: A pattern mechanism for a knitting machine which is adapted to selectively control longitudinal movement of needles in their slots. The needles are provided with jacks in operating relationship thereto for moving the needle in a longitudinal direction. A separate butt element is carried by the jack and is movable relative to the jack both longitudinally and transversely in at least two alternate modes. One of the modes provides lesser longitudinal free movement of the butt element relative to the jack body than the other of the modes. All of the butt elements carried by a series of jack bodies are cammed to the mode which permits greater longitudinal free movement. Selected ones of the butts are moved to the mode providing lesser longitudinal free movement so that only the jack bodies carrying the selected butt elements will be elevated by a raised cam.

Abstract: An automatic clothes washing machine of a single-tub construction with water level sensing and liquid extraction features includes scoop conduits arranged symmetrically within the sump chamber of a reversely tapered tub i.e., divergent from top to bottom. Each scoop conduit has an opening in its end adjacent the outer wall of the sump chamber and is connected to a discharge line along the axis of the tub. When the tub spins, liquid is forced radially outwardly and downwardly and exits through the scoop conduit openings into the discharge line while maintaining a dynamic balance of the tub. Liquid level control is regulated by a pressure sensitive valve means communicating with an air dome in an agitator portion of the tub.

Abstract: A cylinder lock comprising an outer cylinder enclosing a hollow rotatable inner cylinder which, in turn, encloses a plurality of locking discs turnable with the key of the lock. Between the outer cylinder and the peripheral edges of the locking discs there is a locking bar locking the inner cylinder to the outer cylinder. This bar is movable from a position locking the inner cylinder, in which position the bar is located partly in a groove in the inner wall of the outer cylinder to a position releasing the inner cylinder. In the latter position the locking bar is received in a channel formed jointly by locking bar notches in the peripheral edges of the locking discs when the discs are brought to a certain position. The groove in the inner wall of the outer cylinder is provided with a lateral step, so that a deep groove portion and a shallow groove portion are formed.

Abstract: A door lock having two escutcheon plates clamped against the sides of a door, two mortise cylinders mounted in coaxial relation in the escutcheon plates and each having a rotatable key plug and an actuating arm on the inner end of the plug, a bolt slidable between extended and retracted positions, and a toggle joint bolt-operating mechanism actuated by the actuating arms on the key plugs. This mechanism includes a bolt link pivotally connected to the inner end of the bolt, and an actuating link between the ends of the key plugs having abutment means for coupling and uncoupling of the arms and the actuating link which is urged in toward the locked and unlocked positions by a toggle spring movable into oppositely over-center positions. The abutment means comprise two spaced tabs defining a slot into which the actuating arm is eccentrically extended and retracted during rotation of the key plug through full locking and unlocking revolutions.

Abstract: Two or more doors leading to a single room are provided with electrically operated locks which are energized by depressing a button in the room. All of the locks are de-energized by opening either of the doors, so that access to the room is available through either of the door openings when the room is not occupied.

Abstract: In a magnetic lock of the type having at least one tumbler pin pivotally supported on a mounting plate and a locking plate having an opening arranged to receive one end of the tumbler pin when an opposite end of such pin is attracted by a permanent magnet device carried by a key, the improvement wherein the opposite end of the tumbler pin is formed with a transversely enlarged head portion and the mounting plate is formed with abutment devices arranged to engage with the head portion to insure that the one end of the tumbler pin accurately "points" towards the opening of the locking plate.

Abstract: The device covers the ignition lock which is conventionally mounted on the vehicle steering column and comprises a lock housing and a C-shaped band received by the lock housing which together cooperate to form a shroud or cover for the ignition lock. The housing has a pair of latching devices for receiving the band and locking the band relative to the housing. The latching devices are operated from a key lock which permits release of the latching devices. The housing is positioned so that the key lock faces the vehicle dashboard so that there is little space between the key receiving lock and the dashboard thereby making it difficult for an unauthorized person to "jimmy" the lock open using a prying device or the like.

Abstract: The feed mechanism for a pilger or Mannesmann rolling mill is driven by an electrical linear motor which is controlled on the basis of two pulse trains. One train is derived from the rolls, the other one from the reciprocating motor. The control is carried out to distinguish between a constant speed phase during a rolling pass, an acceleration phase for advancing the feed mechanism and a deceleration phase to obtain reversal ahead of re-engagement of the bloom by the rolls for the next rolling step.

Abstract: A stretch-forming machine in which a work piece is clamped at either end to hydraulic tensioning actuators, the actuators being pivotally supported at the ends of control arms that move the actuators through predetermined arcuate paths relative to a stretch die. The movement of the control arms wraps the work piece around the die while the actuators adjust for differences in the path of the work piece ends and the arcuate path of the control arms. The actuators stress the work piece to maintain it under controlled tension. The actuators are controlled as a function of arm position by cables extending between the center of the die and the pivotal supports of the actuators on the control arms. The cables wrap around the surface of the die as the control arms swing through their arcs. Linear transducers generate output signals that correspond to any changes in length of the cables between the die and the pivot points on the control arms due to the movement of the control arms relative to the die.

Abstract: There is provided a prestressed universal rolling mill of a type in which a housing is divided into three parts, i.e., an upper cross beam carrying a top horizontal roll, an intermediate frame carrying vertical rolls and a lower cross beam carrying a bottom horizontal roll, and these three parts are clamped together by means of tension bars, whereby after the clamping force on the housing has been released, the tension bars are rotated to simultaneously move the upper and lower cross beams the same distance in different directions, thereby making it possible to readily adjust the position of the top and bottom horizontal rolls and making the construction of the roll stand itself compact and rigid.

Abstract: A method and apparatus are provided for use in converting readily- available steel tubing blanks into components having enhanced mechanical properties suitable for use in pressure vessels and the like, and more particularly the invention provides further apparatus and a method to convert such components into pressure vessel bodies.

Abstract: A sheet metal bending brake apparatus adapted to make complex bends in a sheet metal workpiece, comprising a frame, a fixed holding bar mounted adjacent of said surface, a movable holding bar mounted on said frame movable between a forward clamping position in opposed clamping relationship with the fixed bar and a rearward and downward position below the plane of the fixed surface, a bending brake element adjacent the fixed jaw adapted to contact sheet metal held between the same, said bending element adapted to rotate 180.degree., or more, around a point adjacent the jaws, the movable holding bar being coordinated with the bending brake to release from the holding position before the bending brake has rotated 180.degree..

Abstract: Press apparatus including a blank holding ram and a drawing ram which are reciprocally driven such that the holding ram can hold a blank of material while the drawing ram moves relatively to the holding ram to perform a drawing operation on the blank. Stops are provided for limiting the movement of the holding ram with pressure fluid cushions being arranged in the drive train for the holding ram so as to accommodate a dwell phase with the holding rams against the stops during the drawing operation.

Abstract: Method and apparatus for automatically straightening elongated and at least partly rotationally symmetrical workpieces by applying a sequence of straightening strokes to a workpiece at each of a plurality of straightening stations to counteract a deformation until the measured instantaneous values of the deformation fall within a predetermined deformation tolerance. The depth of the straightening strokes is determined by the difference between the measured instantaneous values of the deformation and the mean of the maximum and minimum values of the deformation.

Abstract: The forging press has a horizontal drive shaft on which is carried an eccentric body linked to a vertical force-transmitting block whose lower surface lies at an angle to the horizontal and flushly engages the top of a horizontally reciprocal wedge whose bottom surface lies on the hammer. Interfitting ridges and grooves interconnect the wedge, the force-transmission block, and the hammer so that the hammer hangs from the wedge and the wedge from the force-transmission block. A spindle threaded into the wedge is rotatable to establish its horizontal position, and, therefore, to set the relative position of the force-transmission block in the hammer. At its other end this spindle is provided with a piston reciprocal in a horizontally extending hydraulic chamber which is maintained under a predetermined pressure. The threshold at which the wedge may slip to the side and protect the hammer from overloading is established by the pressure in this hydraulic cylinder.

Abstract: A mounting for a long horizontally disposed reciprocal ram of a can forming machine. The ram which carries a punch or mandrel at one end and is connected to a reciprocating drive at its other end is supported intermediate its ends from the machine framework by a plate which slides in a guideway. The plate, which extends parallel to the ram longitudinally thereof has a fixed connection at one end with the ram which is suspended beneath the plate. The plate which runs on guideways becomes very hot and is free to expand longitudinally independently of the ram since it has creep-accommodating connections through high thermal resistors with the ram at longitudinally spaced points which freely permit such expansion and resist transmission of heat into the ram.

Abstract: Billet material is extruded through a die having a plurality of die apertures thereby to produce simultaneously a plurality of extruded products such as wire. In one embodiment, the die has a conical mouth with a first die aperture at the apex thereof and with a plurality of radially equispaced second die apertures located forwardly of the first die aperture, the second die apertures having bevelled entries at the inlet ends thereof communicating with the conical mouth. In another embodiment, the die has multiple aperture groupings arranged therein, each grouping having a central die aperture and a plurality of peripheral die apertures radially equispaced about the central die aperture.

Abstract: An apparatus is disclosed for testing the traction properties of pneumatic tires. A frame is provided having a plurality of structural members. A suspension system having upper and lower arms each having first and second ends is rotatably attached to the frame at the first ends of the upper and lower arms. A hub assembly having a triaxial force transducer mounted therein is attached to the second ends of the suspension system by means of a pair of spherical bearings. An aperture extending through a rear wall of the hub assembly, through the triaxial force transducer and through a front wall of the hub assembly supports a driven axle for applying driving or restraining torque to a pneumatic tire mounted on the front surface of the hub assembly.

Abstract: The output of an oxygen sensor is fed in parallel to the inputs of amplifiers having amplification in different portions of the sensor output range and having different gain. The amplifier outputs are combined in a summing circuit. The result is to smooth out the characteristic of the measurement and to produce a signal that can drive an indicator to provide a meaningful indication in terms of air number. The temperature of the oxygen sensor must be regulated or compensated for for good results.

Abstract: A method and device for contactless measuring of the thickness of layers, particularly of insulating layers on metallic parts whereby a contactless pneumatic servo-mechanism approaches to and maintains a measuring head at a predetermined distance from the layer and whereby the thickness of the layer is ascertained by a measuring pick-up located in the measuring head.

Abstract: A fluid pressure comparison apparatus including a pressure responsive member displaceable by the difference between two pressure sources being compared to vent fluid from one of the sources, when its pressure is greater than the other, through a port whose aperture is varied by the displacement of the pressure responsive member. The flow of vented fluid is measured in one of many possible ways to determine the excess pressure. The measurement may be displayed on an indicator or applied to control associated equipment. Various arrangements embodying the apparatus may be used for flow indication, flow control, leakage detection and indication and as warning or control equipment. The pressure responsive member is shown as a nylon reinforced rubber diaphragm but the nature of the member will depend on the absolute as well as the relative values of the pressures compared.

Abstract: A testing apparatus for cigarettes or the like has a rotary drum having axially parallel flutes for cigarettes, at least one ring-shaped carrier which is adjacent to one end and is driven at the speed of the drum about an axis which makes a small acute angle with the axis of the drum so that successive increments of the carrier approach the respective end of the drum during travel toward a testing station and move away from the drum during travel beyond the testing station. The carrier supports engaging elements in the form of pins or elastic sleeves which engage the adjacent ends of cigarettes during travel past the testing station. The pins can penetrate into relatively soft fillers of cigarettes and thereby cause a transducer to produce signals which are used for segregation of the respective cigarettes. The sleeves can engage the ends of wrappers of cigarettes during travel past the testing station to admit into the fillers a pressurized testing fluid or to draw a testing fluid through the fillers.

Abstract: A pipeline closing head, for use in testing a pipeline after it has been laid on a submerged bed by subjecting the pipeline temporarily to internal pressure through the use of filling and emptying balls, is constituted by a hollow cylindrical body having a crowned closing element at one end and containing, at its other end, an air tight chamber housing the filling and emptying balls. Ducts and control valves through which fluid is supplied to said chamber to activate the filling and emptying balls and supply fluid pressure to the interior of the pipeline are housed within the cylindrical body so that they do not overhang the closing head, which may slide along a conventional ramp for the pipeline.

Abstract: A pulse reflection type ultrasonic thickness meter having an ultrasonic transducer which supplies an ultrasonic pulse wave to an object to be measured and receives an echo pulse from the object and a counter which counts the time difference between the transmission of the ultrasonic pulse wave and the echo pulse. In this case, a switching circuit is provided which controls the counter in such a manner that a power source is disconnected from the counter during a non-measurement time period.

Abstract: An electro-dynamic shaker and a pendulum system which has a resonant frequency lower than the lower limit of the frequency band of ordinary floor vibrations are fixedly mounted on a base plate. The pendulum system comprises a pendulum, damper and a differential transformer for detecting the relative displacement between the pendulum and the output shaft of the shaker. The detected relative displacement is compared in a control device with an input signal, the difference obtained by the comparison being used as a negative feedback signal to correct the input signal to be fed to the shaker to thereby stably produce minute vibration.