Abstract: In order to provide a vibration testing apparatus which can have a large diameter without introducing undesirable rigid vibration modes, the vibration testing apparatus 1 comprises a support 2, at least one electromagnetic vibration generator 12 mounted on the support, the mounting comprising an annular body 5 and a head expander 10, the annular body being supported by bearings located around the periphery of the annular body 5.

Abstract: An armature for an actuator for applying vibration to a body along an axis, the armature having at least two parallel wound helical windings on the axis, and a terminal arrangement connected to the ends of the windings for selective connection of the windings to two external A.C. drivelines, the terminal arrangement being switchable between a relatively low impedance mode, with at least two of the windings connected electrically in parallel, and a relatively high impedance mode, with two of the windings or two groups of parallel-connected windings connected in series.

Abstract: A switch-mode power amplifier circuit using high power, low distortion waveforms is connected to an electromagnetic load to provide a high degree of control over the load. The circuit comprising a plurality of half-bridge networks having outputs combined at a summation point. The half-bridge networks are switched to provide power outputs sequenced to generate an interlaced output at the summation point which is operably connected to the load so that for a given switching frequency of the networks the operational frequency of the circuit is increased. The sequencing of the half-bridge outputs to generate an interlaced output facilitates the reduction of the switching frequency of individual switching components within the half-bridges while at least maintaining the overall operational frequency of the circuit. For N half-bridges operating at ƒkHz, the overall operational frequency of the circuit is NƒkHz.

Abstract: An armature for an electromagnetic vibration generator is suspended at its periphery by a plurality of circumferentially spaced flexure members each connected to the vibrator stator by means of an anchoring bracket having a floating part connected to the outer end of the flexure member and a stationary part connected to the stator. The brackets are provided with recesses in each of which is located a resilient member of elongate form. The recesses have closed ends so as to reduce the tendency of the material of the resilient members to migrate during operation of the vibration generator as well as to provide rotational stiffness for the complete armature suspension assembly.

Abstract: An electromagnetic vibration generator or shaker comprises an armature suspended from a stator and having a coil carried by the armature located in an air gap in the stator. A D.C. magnetic field is produced across the air gap and when an alternating current is fed through the armature coil the armature virbrates along its longitudinal axis. According to the invention the armature is suspended at its periphery by a plurality of suspension members which are arranged in pairs and allow free movement of the armature along its axis of vibration. However the two members of each pair are arranged at an angle to each other and exhibit a stiffness to lateral movement of the armature so as to restrain turning forces acting on the armature in either direction of rotation.

Abstract: An armature structure for an electrodynamic shaker comprises an armature support and an armature coil assembly mounted on the support. The coil assembly includes a cladding, or alternatively a spine, of a carbon fibre material. Preferably the carbon fibres extend generally longitudinally of the armature, that is to say in its direction of motion.

Abstract: Vibration testing apparatus comprises a vibration generator coupled to a horizontal slip plate by means of a driver bar, having limbs which embrace opposite sides of the slip plate. The lower limb of the driver bar is separable from the remainder of the driver bar so as to enable the vibration generator and the remainder of the driver bar to be pivoted away from the slip plate without lateral displacement of the slip plate along its horizontal axis.