Device and arrangement for the mechanical excitation of parts to be acoustically tested with high repetition frequency and constant intensity

Abstract

Electronic-mechanical arrangement for moving a clapper (8) to excite test specimens for an acoustic test, characterized by the following properties: - The clapper is moved purely linearly. The axially movable plunger mechanism (2) is guided at two points by a sliding bushing (3). - Encapsulated design with separate compartments for mechanics and electronics - Use of multiple coil windings (6) either to increase and precisely control the clapper acceleration or to measure the clapper speed or the hammer position in the system - Use of a pressure equalization element (1) to prevent an air pump effect caused by the moving pushrod (2) that carries the clapper. Dirt and moisture are kept away from the mechanism by the pressure equalization element. - Equipping the plunger with a permanent magnet (5) to define the direction of movement via the external magnetic field generated by the coil windings - Simple and separate interchangeability of the coil unit and the plunger as a whole through axial removal of the stator and the plunger against or in the "knocking direction"; thus also interchangeability of the mechanics without removing the entire system (from the production environment) - Use of a ferromagnetic sleeve (4) with thermal coupling to the device housing (7) to enhance the magnetic field, reduce magnetic losses and increase heat dissipation

Description

[0001] The invention relates to a device (“excitation unit”) and an arrangement used therein for the acoustic testing of the properties of test specimens that can be acoustically activated by one or more strikes. A clapper is moved in an electromagnetically controlled manner and delivers strikes of defined energy to the surface of the test specimen. From the emitted acoustic energy of these test specimens, excited to natural vibrations, conclusions can be drawn about the geometric or material properties of the test specimens themselves or their contents – for example, if they are containers – using known methods. Due to the special design of the clapper drive and its bearing, the delivery of strikes in a significantly faster sequence, with defined intensity, and with more efficient utilization of the supplied electrical energy is possible than is currently the case with prior art designs of clapper drives in acoustic excitation units. [Purpose of the invention]

[0002] The invention is based on the objective of increasing and controlling both the transmissible excitation energy and the possible repetition frequency of the delivered impacts by means of a suitable extension and design of the known excitation of the test specimen by means of a mechanical impact. In addition to the improved testing method, this also makes it possible to test heavier and acoustically damping test objects. [State of the art]

[0003] Acoustic resonance analysis is now considered a standard method for verifying the material and geometric properties of test specimens, both as individual parts and as composite elements or structures, but also for measuring secondary effects that influence the resonance of these test specimens, such as measuring the fill level or internal pressure of a closed container by measuring the resonance of the container or its closure itself.

[0004] Due to their material and geometric properties, and also due to these secondary parameters, such as their clamping, the ambient temperature, the available resonance space (fill level), or the pressure to which they are subjected, the test specimens develop one or more characteristic acoustic resonances, the measurement of which allows conclusions to be drawn about these properties, such as material defects, geometric deviations, or the secondary parameters - such as the internal pressure of the container.

[0005] The acoustic signal of the test specimen to be examined can be generated during operation, such as in the case of a motor or pump, or produced by suitable excitation for testing. Typical excitation methods include the free fall of the test specimen onto an impact plate, excitation by a mechanical impulse, such as the clapper of a bell, excitation by an acoustic source such as a loudspeaker or a dynamic, electromechanical vibration exciter, an electrical pulse, or, in the case of ferromagnetic test specimens, non-contact excitation by a magnetic pulse.

[0006] The excitation of vibration by a mechanical impact according to the state of the art is limited in particular by the fact that the generated impact energy, its repeatability and the impact frequency do not meet the requirements for a high-speed test in continuous industrial mass production. Reference symbol list 1 pressure equalization element 2 Pushrod 3 sliding bushing 4 Sleeve 5 permanent magnets 6 magnetic coils 7 cases 8 clappers

Claims

[1] Electronic-mechanical arrangement for moving a clapper (8) to excite test specimens for an acoustic test, characterized by the following properties: - The clapper is moved purely linearly. The axially movable plunger mechanism (2) is guided at two points by a sliding bushing (3). - Encapsulated design with separate compartments for mechanics and electronics - Use of multiple coil windings (6) either to increase and precisely control the clapper acceleration or to measure the clapper speed or the hammer position in the system - Use of a pressure equalization element (1) to prevent an air pump effect caused by the moving pushrod (2) that carries the clapper. Dirt and moisture are kept away from the mechanism by the pressure equalization element. - Equipping the plunger with a permanent magnet (5) to define the direction of movement via the external magnetic field generated by the coil windings - Simple and separate interchangeability of the coil unit and the plunger as a whole through axial removal of the stator and the plunger against or in the "knocking direction"; thus also interchangeability of the mechanics without removing the entire system (from the production environment) - Use of a ferromagnetic sleeve (4) with thermal coupling to the device housing (7) to enhance the magnetic field, reduce magnetic losses and increase heat dissipation [2] Arrangement according to 1., but additionally characterized by a split pushrod that allows the permanent magnet to be replaced - for example, to adapt to different ambient temperature conditions.

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