Device and Method for Ascertaining Mechanical Properties of a Test Body

Abstract

The invention relates to a device for ascertaining mechanical properties, for example, the natural frequency, the damping or the natural vibration mode of a test specimen containing ferromagnetic material components, in particular a brake pad for a motor vehicle. An electromagnetic actuator, in particular an electromagnet, is provided for exerting a magnetic attractive force onto the test specimen so that the actuator exerts a force impulse that imparts the test specimen with vibrations whose spectrum of vibration contains at least one natural frequency vibration of the test specimen.

Claims

1. A device (10) for ascertaining mechanical properties of a test specimen (1) containing ferromagnetic material components, comprising: an electromagnetic actuator (2) configured to exert one or more force impulses of a magnetic force of attraction onto the test specimen (1) so that the test specimen (1) vibrates and a vibration spectrum of such vibrations contains at least one natural frequency vibration of the test specimen (1).

2. The device (10) according to claim 1, further comprising a holding device (11), wherein the electromagnetic actuator (2) is held in or on the holding device (11) and suspended opposite from the test specimen (1) prior to activating the electromagnetic actuator (2).

3. The device (10) according to claim 2, wherein the electromagnetic actuator (2) is held on the holding device (11) with at least one damping element (9).

4. The device (10) according to claim 1, further comprising a transport mechanism for transporting several test specimens (1) arranged one after the other through the device (10), and wherein the electromagnetic actuator (2) exerts the magnetic force of attraction onto the test specimen (1) cyclically.

5. The device (10) according to claim 4, wherein the transport mechanism is made of a non-ferromagnetic material.

6. The device (10) according to claim 1, wherein the actuator (2) has an actuation head (3) configured for introducing the force impulse into the test specimen (1).

7. The device (10) according to claim 1, further comprising a sensor unit (5) for optically and/or acoustically detecting the natural frequency vibrations of the test specimen (1) that is excited due to application of the one or more force impulses onto the test specimen (1).

8. The device (10) according to claim 7, wherein the sensor unit (5) has a force sensor (7) configured to measure a force-over-time function during application of the one or more force impulses.

9. The device (10) according to claim 1, further comprising a control unit (6) configured for controlling the actuator (2) and/or for synchronizing the sensor unit (5) with the introduction of the one or more force impulses into or onto the test specimen (1).

10. The device (10) according to claim 1, further comprising an evaluation means (8) configured for comparing, calculating and/or checking data that has been measured by the sensor unit (5) and/or data that has been stored.

11. The device according to claim 1, wherein the electromagnet actuator (2) has an actuation head (3) that is substantially dome-shaped or pyramid-shaped.

12. A method for ascertaining mechanical properties of a test specimen (1) containing ferromagnetic material components, comprising: exerting a magnetic force of attraction onto the test specimen (1) with an electromagnet actuator (2) or electromagnet in order to introduce a force impulse into the test specimen (1) so as impart the test specimen (1) with vibrations whose spectrum contains at least one natural frequency vibration of the test specimen (1); and optically and/or acoustically detecting the natural frequency vibration(s) of the test specimen (1) upon excitation of the test specimen (1) with the force impulse from the electromagnet actuator (2) or electromagnet.

13. The method according to claim 12, wherein the test specimen (1) is substantially free of vibration before the electromagnetic actuator (2) or electromagnet is actuated.

14. The method according to claim 12, wherein natural frequencies that belong to a natural vibration of the test specimen (1) are measured and the measured natural frequencies are compared to reference values.

15. The method according to claim 14, further comprising determining a compressibility parameter of the test specimen (1) by comparing the measured natural frequencies to reference values of natural frequencies for other test specimen with known compressibility parameters.

16. The method of claim 15, wherein the test specimen (1) is a brake pad for a motor vehicle.

17. The method of claim 12, further comprising transporting several test specimens arranged one after the other to be vibrated by exerted magnetic force from the electromagnetic actuator or electromagnet, wherein the magnetic force of attraction is exerted onto the test specimens cyclically.

18. A device for determining mechanical properties of a brake pad for a motor vehicle, comprising: an electromagnetic actuator or electromagnet to exert a magnetic force of attraction onto the brake pad by a force impulse to impart the brake pad with vibrations having a spectrum of frequencies that contains at least one natural frequency vibration of the brake pad; a holding device that includes at least one damping element to suspend the electromagnetic actuator or electromagnet in position spaced apart from the brake pad; and a sensor unit to optically and/or acoustically detect the natural frequency vibrations of the brake pad while the brake pad is vibrated in response to the magnetic force impulses exerted thereon by the electromagnetic actuator or electromagnet.

19. The device of claim 18, wherein the sensor unit is a sensor selected from the group consisting of: a microphone and a laser vibrometer.

Description

DESCRIPTION OF THE DRAWINGS

[0057] In this context, the following is shown, at times schematically:

[0058] FIG. 1 the device for ascertaining mechanical properties of a test specimen in a first position a) in a side sectional view and b) in a sectional view from the top,

[0059] FIG. 2 the device as shown in FIG. 1 a) in a second position, and

[0060] FIG. 3 a schematic circuit diagram of the device as shown in FIG. 1.

DETAILED DESCRIPTION

[0061] For the sake of clarity, identical components or those having the same effect are provided with the same reference numerals in the figures of the drawing shown below.

[0062] FIG. 1 shows a device 10 for ascertaining mechanical properties, for instance, the natural frequency, the damping or the natural vibration mode, of a test specimen 1 containing ferromagnetic material components, especially a brake pad for a motor vehicle. An electromagnetic actuator 2, especially an electromagnet 4, is provided for exerting a magnetic force of attraction onto the test specimen 1.

[0063] This magnetic force of attraction is dimensioned in such a way that the test specimen 1 is attracted in the direction of the actuator 2, so that, due to the magnetic force of attraction, the actuator 2 exerts a force impulse onto the test specimen 1. The force impulse imparts the test specimen 1 with vibrations whose spectrum contains at least one natural frequency vibration of the test specimen 1.

[0064] As can be seen in FIGS. 1 and 2, the actuator 2 is arranged so as to be suspended opposite from the test specimen 1 by means of a holding means 11. In the present embodiment, the actuator 2 is fastened with a screw 12 to the holding means 11, so that the actuator 2, in its operating position, is suspended above the components or test specimens 1 that are to be checked.

[0065] The actuator 2 is also held on the holding device 11 by means of two damping elements 9. These damping elements 9 can be configured as washers in order to damp the vibrations generated by the force impulse inside the device 10, so that a high level of stability is ensured for the device 10 during operation.

[0066] The actuator 2 has an actuation head 3 that serves to introduce the force impulse into the test specimen 1. Due to its impact momentum, this actuation head 3 produces a flat, continuous spectrum. The actuation head 3 can be configured so as to be essentially dome-shaped or pyramid-shaped. The duration or mode of the excitation spectrum results from the weight and stiffness of the actuation head 3 as well as from its structure.

[0067] The use of actuation heads 3 made of various materials makes it possible to adapt the exciter spectrum to the frequency range that is to be examined.

[0068] The actuation head 3 can essentially be made, for example, of steel or plastic or rubber.

[0069] The holding device 11 having the actuator 2 can be used in an existing industrial production line for purposes of the quality assurance of components in that the device is arranged, for example, on a transport mechanism, especially a conveyor belt.

[0070] At the point in time of the activation of the actuator 2, the magnetic force of attraction acts upon the test specimen 1, attracting it in the direction of the suspended actuator 2, in other words, upwards, as shown in FIG. 2. If the magnetic force of attraction has been properly dimensioned, the test specimen 1 strikes the actuation head 3 of the actuator 2 so that the force impulse is exerted onto the test specimen 1, and mechanical excitations are introduced into the test specimen 1. The duration of the impact of the test specimen 1 against the actuation head 3 is relatively short and falls within the hundredth of a second or millisecond range.

[0071] Since the actuator 2 is arranged so as to be suspended, free vibrating conditions exist for the test specimen 1 when the test specimen 1 comes into contact with the actuator 2. After all, the test specimen 1 is brought into a so-called floating state at the point in time of the force impulse. In this floating state, the test specimen 1 is dynamically isolated from the physical environment and is not in contact with any other surfaces. For this reason, there is no need for a suspension or for elastic placement of the test specimen 1 by means of foam pads or the like.

[0072] The use of an electromagnet 4 to excite the natural frequencies in the test specimen 1 is advantageous since the magnitude of the magnetic force of attraction as well as the duration of the activation can be set in such a way that, although the test specimen 1 is attracted towards the actuation head 3, it is prevented from adhering to the electromagnet 4. Moreover, the control of the electromagnet 4 prevents the test specimen 1 from striking the actuation head 3 multiple times.

[0073] When it comes to industrial production processes, the device 10 can be integrated very easily and effectively even into existing production lines. Normally, such production lines have a transport mechanism to transport several components arranged one after the other.

[0074] By means of the actuator 2 of a device 10 that has been integrated in this manner, the magnetic force of attraction needed for a force impulse is exerted onto the test specimen 1 to be analyzed. During this time, the other test specimens 1 that are still present on the transport mechanism are moved along by means of the transport mechanism. After the force impulse onto the test specimen 1 has been executed, the actuator 2 is de-energized, so that the test specimen 1 drops back onto the transport mechanism and is conveyed further before the next test specimen is magnetically attracted.

[0075] Owing to the cyclical application of the magnetic force of attraction onto the test specimens 1, they can be continuously conveyed further by the transport mechanism. A prerequisite for this is that the distance between adjacent test specimens 1 has to be selected in such a way that the test specimens 1 do not collide with each other, for example, if the next test specimen 1 is already passing the device 10 while an analysis of a test specimen 1 is still ongoing.

[0076] In order to avoid measuring errors and malfunctions during the analysis, the transport mechanism can be made of a non-ferromagnetic material.

[0077] As the schematic view depicted in FIG. 3 shows, a sensor unit 5 serves to optically and/or acoustically detect the natural frequencies of the natural frequency vibrations of the excited test specimen 1. The measurement of the vibration of the test specimen 1 can be carried out by means of a sensor unit 5 such as, for instance, a vibration sensor, especially a microphone or a laser vibrometer. The trigger of this sensor 5 can be synchronized with the start of the force impulse. For this reason, the device 10 can have a control unit 6 for controlling the actuator 2 and/or for synchronizing the sensor unit 5 with the introduction of the force impulse into the test specimen 1.

[0078] In addition, the sensor unit 5 can have a force sensor 7 to measure a force function. This force sensor 7 can be connected in series to the actuator 2 in order to detect the force function during the force impulse. The measurement of the force signal provides information about the force and the spectrum of the force impulse. For example, the signal from the microphone or laser vibrometer can be mathematically reconciled with the signal of the force sensor 7 in order to correct for uneven excitations.

[0079] For purposes of evaluating the measured data, an evaluation unit 8 is provided in which the measured data is compared to reference data that, for example, had been previously stored, in order to ascertain whether an analyzed test specimen 1 exhibits a defect and conceivably needs to be segregated. Moreover, the measured data can be converted and/or checked in the evaluation unit 8.

[0080] If the test specimen 1 is a brake pad that has a brake pad carrier plate with a friction lining arranged on it, the test specimen is magnetically attracted with the brake pad carrier plate side towards the actuation head 3 of the actuator 2, so that the force impulse is introduced onto the carrier plate side of the brake pad. This causes the brake pad to vibrate. These vibrations are then analyzed, as already described above. On the basis of the natural frequencies of the brake pad measured in this manner, conclusions can be drawn about the compressibility of the brake pad and about the state of the brake pad. This measurement allows an evaluation of each component as to whether it is flawless or whether it has a defect. The defective components can be removed from the further production process by means of an ejection apparatus.

[0081] The measured or calculated data can be employed to monitor a manufacturing process, to segregate components that fall outside of a defined scatter band or else in order to detect flaws.

[0082] It is not necessary to remove individual pads in order to carry out a quality analysis since all of the pads are checked by the device for ascertaining mechanical properties.

[0083] Therefore, on the basis of the invention, it is possible to carry out a natural frequency test that can be implemented quickly and cost-effectively and especially advantageously in one hundred percent of the components during large-scale production, particularly brake pad production. For this reason, the present invention makes a major contribution to the automation and standardization of the modal test of ferromagnetic test specimens 1.

LIST OF REFERENCE NUMERALS

[0084] 1 test specimen

[0085] 2 electromagnetic actuator

[0086] 3 actuation head

[0087] 4 electromagnet

[0088] 5 sensor unit

[0089] 6 control unit

[0090] 7 force sensor

[0091] 8 evaluation unit

[0092] 9 damping element

[0093] 10 device

[0094] 11 holding device

[0095] 12 screw