An improved impact device for impact excitation measurements.

Abstract

The present invention relates to an impact device for applying an instantaneous impact to a workpiece during impact excitation measurement, comprising: an elongated, elastically bendable arm elastically deformable around a bending direction having a longitudinal proximal end and a longitudinal distal end; a hammer tip attached to the distal end of the arm for mechanically impacting the workpiece; and a programmable actuator attached to the longitudinal proximal end of the arm, wherein the actuator is programmed to impart an angular velocity to the longitudinal proximal end of the arm by rotating the longitudinal proximal end around an actuator axis essentially parallel to the bending direction of the arm, wherein the angular velocity follows a predetermined angular velocity profile, the angular velocity profile being configured to apply an instantaneous impact to the workpiece.

Description

[Technical field]

[0001] The present invention relates to an improved hammer for delivering an impact to a workpiece when performing impact excitation measurements. The present invention therefore relates to the field of impact excitation measurements, in which information about a workpiece is obtained by measuring and analysing the vibration response to a mechanical impact, in particular an instantaneous impact. The instantaneous impact is delivered by a hammer.

[0002] background Impact excitation techniques for characterizing workpieces are known from the following documents:

[0003] Document EP 3658868 discloses an apparatus for analysing the mechanical vibration response of a solid material sample, comprising an array of impactors arranged to apply impacts to respective well-defined points on the surface of said solid material sample, a sensor arranged to capture said mechanical vibration response as a time-varying signal following the impact of at least one impactor, and processing means arranged to analyse said time-varying signal to determine frequencies and damping constants of sine waves constituting said time-varying signal. The invention also relates to a corresponding method of characterising a solid material sample.

[0004] Document WO2020254698 discloses a method for acoustically measuring material properties of a test specimen at high temperatures, comprising the steps of: a. heating the test specimen within a test temperature range; b. performing background measurements within said test temperature range by capturing a vibration signal from the test specimen within a calibration period, thereby obtaining a noise signal; c. performing acoustic measurements on said test specimen within said test temperature range and within a test period, c1. by applying a vibration excitation to the test specimen, c2. by capturing a vibration signal of the test specimen within a test period, thereby obtaining a vibration response signal to said vibration excitation; and d. obtaining material properties of the test specimen by analyzing the vibration response signal, thereby taking into account the noise signal. The invention also relates to a system for acoustically measuring material properties of a test specimen at high temperatures.

[0005] Both prior art documents in the applicant's name relate to methods and devices for performing impact excitation (IE) measurements.

[0006] IE techniques essentially consist of impacting the workpiece and acquiring and analyzing the vibration response signal, also called the acoustic response signal. The response signal can be captured via several methods, including using microphones, piezoelectric displacement sensors and / or laser interferometers.

[0007] The impact delivered to the workpiece should be as clean as possible to reduce noise signals. In principle, it is desirable to deliver an instantaneous impact to the workpiece using an impact delivery mechanism that does not generate noise itself. The impact delivery mechanism typically comprises an impactor that mechanically delivers an impact to the workpiece and an impactor actuator that provides kinetic energy to the impactor to deliver the impact. In the prior art, ballistic impactors are used, which are given momentum by an impactor actuator, after which the impactor follows a ballistic trajectory for at least a short period of time before impacting the workpiece. After impact, the ballistic impactor may follow a ballistic trajectory again before being recaptured. The use of ballistic impactors has the advantage of allowing essentially instantaneous impacts, i.e. impacts that are a very short contact period during which the kinetic energy of the impactor is mechanically transferred to the workpiece. In practice, noise may be generated due to: -Multiple impacts: for example the inertia of the impactor causes the workpiece surface to vibrate faster than the impactor can retract from the workpiece, so that the impactor contacts the workpiece more than once. In the case of a ballistic impactor this also means that the impact is preferably applied from below the workpiece, so that the impactor does not bounce off the workpiece more than once.

[0008] Impactors may generate noise when actuated, typically due to friction between the impactor and the impactor actuator. In the case of ballistic impactors, the impactor actuator may include a barrel or guide to ensure that the ballistic impactor is imparted with velocity in the correct direction. Friction with the barrel or guide may cause noise.

[0009] The impactor may produce noise after impact, for example by touching other parts of the device or when being recaptured in the case of ballistic impactors.

[0010] In the above prior art documents, ballistic impactors are disclosed as the preferred impactor allowing for instantaneous impact. However, the inventors have found that ballistic impactors are not always the best solution. In particular, ballistic impactors and impactor actuators are not always easily adapted to be used with different types of workpieces. Furthermore, ballistic impactors are best used from below to reduce the possibility of multiple impacts, and therefore may be prohibited from impacting the workpiece from different sides and / or directions. It is noted that this may be required if one wishes to excite or enhance different vibration nodes in the workpiece.

[0011] The present invention relates to -Easily adaptable to deliver instantaneous impact to workpieces of any type of material, geometric shape, size, etc. - can be easily positioned or repositioned to deliver impacts to the workpiece on different sides and / or along different directions; -Reducing noise, especially by essentially eliminating the possibility of multiple impacts and reducing noise due to friction or recapture of the impactor The object of the present invention is to provide an impact delivery mechanism.

[0012] The present invention therefore relates to an improved impact device for performing IE measurements on workpieces and to a method for operating the impact device, which is preferably used in an impulse excitation measurement apparatus, and therefore the present invention also relates to an IE measurement apparatus comprising the impact device.

[0013] Summary of the Invention The invention relates to an impact device, an impact application method and an impact device kit for applying an instantaneous impact to a workpiece in order to perform impact excitation measurements according to claims 1, 3 and 5. The invention also relates to an IE measurement system and a method for performing impact excitation measurements of a workpiece using the inventive impact device and / or method according to claims 5 and 6. Further embodiments of the invention are disclosed in the dependent claims and in the description herein.

[0014] It should be noted that the impact device, the impact method, the IE system and the IE method are interrelated, i.e. the impact method can be performed by the impact device and both can be used by the IE system and the IE method of the present invention, which also means that the features disclosed herein can be applied to all aspects of the present invention.

[0015] The invention is particularly suitable for applying a noise-free or limited noise instantaneous impact to the workpiece, making it possible to carry out clean IE measurements. Moreover, the invention provides an inexpensive solution for the impact device, allowing for easy replacement in case of deterioration or if the characteristics of the impact device, in particular its arm and hammer tip, need to be changed, with respect to the workpiece and / or the IE measurement setup.

[0016] Drawing Overview [Brief description of the drawings]

[0017] [Figure 1] 1 shows an impact device according to the invention. [Figure 2A] 1 shows an impact method and an impact device according to the invention; [Figure 2B] 1 shows an impact method and an impact device according to the invention; [Figure 2C] 1 shows an impact method and an impact device according to the invention; [Figure 2D] 1 shows an impact method and an impact device according to the invention; [Diagram 3] 1 shows an embodiment of an arm according to the present invention. [Figure 4] 4 shows an angular velocity profile according to the present invention. [Diagram 5] 4 shows an angular velocity profile according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Detailed Description of the Invention The invention will now be described in more detail with reference to the figures for illustrating the invention.

[0019] The present invention therefore relates to an impact device for applying a momentary impact to a workpiece during impact excitation measurements.

[0020] Impact excitation measurement methods and systems are described in patent applications EP 3658868 and WO 2020254698. IE typically corresponds to subjecting a workpiece to a mechanical impact in a controlled environment, such as a laboratory. The workpiece can essentially be any type of workpiece, including but not limited to: - Preferably a metallic workpiece comprising or made from a metal or alloy, where the metal may include iron, aluminum, zinc, copper, steel, etc. -Polymer materials such as plastics - 3D printing material, preferably metal, ceramic or polymer, such as polyetheretherketone (PEEK) or polyetherimide (ULTEM™, etc.) - Composite materials, such as plastic-metal composites.

[0021] Most preferably, the workpiece is a 3D printed workpiece and / or the method of the invention comprises the step of 3D printing the workpiece.

[0022] Device (1) - an elongated elastically bendable arm (2) having a proximal longitudinal end (4) and a distal longitudinal end (5) and being elastically deformable about a bending direction (3); a hammer tip (6) attached to the distal end (5) of the arm for mechanically impacting a workpiece (7); a programmable actuator (8) attached to the longitudinal proximal end (4) of the arm (2); wherein the actuator (8) is programmed to impart an angular velocity to the proximal longitudinal end (4) of the arm by rotating said proximal longitudinal end (4) about an actuator axis (9) essentially parallel to a bending direction (3) of the arm, the angular velocity following a predetermined angular velocity profile, said angular velocity profile configured to impart an instantaneous impact to the workpiece.

[0023] The term "instantaneous impact" herein refers to a single elastic bounce imparted to the workpiece during which energy is transferred during the brief period of contact between the hammer tip and the workpiece.

[0024] As a result of the angular velocity profile, the hammer tip follows a hammer tip trajectory configured such that the hammer tip imparts a momentary impact to the workpiece. Preferably, the hammer tip trajectory starts at an offset position relative to the workpiece. Thus, the hammer tip trajectory depends, and preferably only depends, on said position offset, the angular velocity profile and bending characteristics of the bendable arms.

[0025] Please note that in Figures 1 and 2A-2D, the bending direction and actuator axis are shown perpendicular to the page, and the bending direction refers to the direction in which the arm can be bent.

[0026] The flexible arm preferably has a strip-like shape with a length L along the longitudinal direction, a width W, and a thickness T, where L>W>T. The tip (6) is attached to the distal end (5) of the arm (2). Preferably, the arm and the hammer tip are monolithic. Preferably, the arm and / or the hammer tip comprise or are made of plastic, metal, alloy, or a combination thereof. Most preferably, the arm and the hammer tip are monolithic and made of plastic. The shape of the arm and the material properties of the arm are preferably selected to ensure bending of the arm around a bending direction perpendicular to the longitudinal direction, more preferably around the width direction, and most preferably, the shape of the arm and the material properties of the arm are selected to ensure bending of the arm around only the width direction, i.e. the arm only bends around the width direction during the execution of the angular velocity profile.

[0027] In a preferred embodiment, the actuator comprises an electric motor, more preferably a rotary electric motor, preferably with a rotor attached to the proximal end of the bendable arm such that the angular velocity profile of the proximal end of the bendable arm can be determined by the rotor of the electric motor.

[0028] In a preferred embodiment, the angular velocity profile includes a turning point where the angular velocity imparted to the longitudinal distal end of the arm changes sign, said turning point being earlier than the impact on the workpiece. This is particularly preferred to ensure that the whip-like movement of the hammer tip imparts an instantaneous impact to the workpiece. This operation is illustrated in Fig. 1 and Fig. 2A-D. In Fig. 1, the situation is shown at the start of the method, where the flexible arm (2) is essentially stationary and straight or slightly bent (e.g. due to the self-weight of the flexible arm and the hammer tip). The actuator then starts to execute the angular velocity profile. In Fig. 2A, the angular velocity (10) is such that the proximal end of the arm rotates towards the workpiece (7). Due to the inertia of the arm and the hammer tip, the bendable arm bends around the bending direction (3), thereby curving the flexible arm. The angular velocity profile then includes a turning point where the angular velocity (11) imparted to the proximal end (4) of the flexible arm is essentially zero. At the turning point (see FIG. 2B), the actuator stops the rotation of the longitudinal end (4) of the arm (2). However, due to the curvature of the arm and its elasticity, the hammer tip remains moving towards the workpiece. At the moment of impact on the workpiece (see FIG. 2C), the actuator has already applied an angular velocity (12) away from the workpiece to the proximal end (4) of the arm, ensuring that the hammer tip does not impact the workpiece multiple times after the impact. This is shown in FIG. 2D, where the actuator has stopped the rotation of the proximal end of the arm (13). The hammer tip has now moved away from the workpiece and can return to rest according to the situation in FIG. 1, ready to start again for follow-up measurements.

[0029] Preferably, the programmable actuator comprises a programmable computing unit, more preferably an Arduino computing unit or a raspberry pi computing unit. The programmable computing unit can be configured to control an electric motor, preferably a rotary electric motor, and can be programmed to manipulate the electric motor to essentially follow an angular velocity profile.

[0030] 4 shows an angular velocity profile (16) according to the invention. The angular velocity profile starts from rest (ω=0 at t=0) and progresses to a maximum angular velocity (ω max ), which preferably increases continuously until the angular velocity of the arm rotates toward the workpiece, and the angular velocity of the arm rotates away from the workpiece. Note that in the figure, a positive angular velocity indicates that the proximal longitudinal end of the arm rotates toward the workpiece, and a negative angular velocity indicates that the proximal longitudinal end of the arm rotates away from the workpiece. The angular velocity profile includes a turning point (14) at time t2. At a moment t3, later than t2, the hammer tip impacts the workpiece with a single elastic bounce. At this moment t3, the angular velocity is negative, indicating that the proximal end of the arm rotates away from the workpiece. At moment t4, the actuator returns to rest (ω=0).

[0031] It should be noted that the turning point (14) of the angular velocity profile refers to the moment when the angular velocity specifically changes sign from positive to negative, i.e., from rotating towards the workpiece to rotating away from the workpiece.

[0032] Figure 5 shows another angular velocity profile (17) according to the invention. The angular velocity profile preferably starts from rest (ω=0 at t=0). In contrast to the embodiment shown in Figure 4, the angular velocity is negative during a first period (18) that ends at a second turning point (19), which refers to the point where the angular velocity changes sign from negative to positive, i.e., from a rotation away from the workpiece to a rotation towards the workpiece. After the first period (18), the angular velocity essentially follows a similar profile as shown in Figure 4. That is, the angular velocity reaches a maximum angular velocity (ω=0) at time t1. max ) The angular velocity profile includes a turning point (14) at time t2. At a moment t3, later than t2, the hammer tip impacts the workpiece with a single elastic bounce. At this moment t3, the angular velocity is negative, indicating that the proximal end of the arm is rotating away from the workpiece. At moment t4, the actuator returns to rest (ω=0).

[0033] Preferably, the arm is replaceably attached to the actuator, allowing the arm and / or hammer tip to be easily replaced, for example in case of tip deterioration or when a different type of arm and / or hammer tip is required to perform the IE measurement. For example, the arm and / or tip may be replaced with another arm and / or tip having different elastic properties, in particular other bending properties. Another reason for replacing the arm and / or hammer tip is when the workpiece needs to be impacted by another type of hammer tip, for example when a harder or softer tip is required, or when a tip of a different material (e.g. metal instead of plastic) is required for optimal IE measurement of a particular workpiece. In this regard, it is noted that for metallic workpieces one may want to use a hard hammer tip, while for workpieces made from 3D printing materials a plastic hammer tip may be preferred. Thus, the present invention may be used to test a variety of workpieces. Here, the present invention provides: - a set of elongated elastic bendable arms, each elastically deformable about a bending direction, the bendable arms having a proximal longitudinal end and a distal longitudinal end; - a set of hammer tips for mechanically impacting a workpiece, each of the hammer tips being attachable, and preferably attached, to a distal end of an arm of a set of elongated resiliently bendable arms; a programmable actuator replaceably mountable to a longitudinal proximal end of each of the arms; An impact device kit comprising: The actuator is programmed to impart an angular velocity to the proximal longitudinal end of the working arm when the actuator is attached to the proximal longitudinal end of the working arm by rotating the proximal longitudinal end about an actuator axis essentially parallel to a bending direction of the working arm, the angular velocity following a predetermined angular velocity profile, the angular velocity profile configured to impart an instantaneous impact to the workpiece.

[0034] The present invention further relates to an impact excitation (IE) measurement system for measuring a vibration response of a workpiece to an instantaneous impact, the impact excitation (IE) measurement system comprising: an impact device according to the invention, a response recording device for capturing the vibration response of the workpiece to the instantaneous impact; a control unit for controlling the actuator of the impact device and the response recording device; - a support device for holding the workpiece in place; Equipped with.

[0035] The present invention also relates to an impact excitation (IE) measurement method for measuring a vibration response of a workpiece to an instantaneous impact, the method comprising: - supporting the workpiece in a predetermined position; - applying a momentary impact to the workpiece according to the impact method of the invention; - capturing a vibration response of the workpiece to a momentary impact; thereby measuring the vibration response of the workpiece to an instantaneous shock.

[0036] In this specification, the response recording device may preferably comprise a microphone, a piezoelectric displacement sensor and / or a laser interferometer for capturing the vibration response. The response recording device also preferably comprises a processing unit and / or a memory unit for recording and / or analyzing the vibration response.

[0037] The workpiece needs to be supported at a predetermined position, said predetermined position being preferably selected having regard to the angular velocity profile and / or the angular velocity profile being selected having regard to the predetermined position.

Claims

1. An impact device for applying a momentary impact to a workpiece during impact excitation measurement, comprising: an elongated, resiliently bendable arm having a proximal longitudinal end and a distal longitudinal end, the arm being resiliently deformable about a bending direction; a hammer tip attached to the distal end of the arm for mechanically impacting the workpiece; a programmable actuator attached to the proximal longitudinal end of the arm; wherein the actuator is programmed to impart an angular velocity to the proximal longitudinal end of the arm by rotating the proximal longitudinal end about an actuator axis that is essentially parallel to the bending direction of the arm, the angular velocity following a predetermined angular velocity profile; The angular velocity profile is configured to impart an instantaneous impact to the workpiece.

2. 2. The impact device of claim 1, wherein the angular velocity profile includes a pivot point at which the angular velocity imparted to the distal longitudinal end of the arm changes sign, the pivot point being earlier than the impact on the workpiece.

3. 3. An impact device according to claim 1 or 2, wherein the flexible arm has a strip-like shape with a longitudinal length L, a width W and a thickness T, where L>W>T, and the hammer tip is attached to the distal end of the arm (2).

4. The impact device of claim 3 , wherein the bendable arm and the hammer tip are monolithic.

5. 3. The impact device of claim 1, wherein the actuator comprises a rotary electric motor and a programmable computing unit configured to control the rotary electric motor, the programmable computing unit being programmed to operate the rotary electric motor to essentially follow the angular velocity profile.

6. 3. An impact device according to claim 1 or 2, wherein the arm is replaceably attached to the actuator.

7. An impact application method using an impact device for applying an instantaneous impact to a workpiece during impact excitation measurement, the impact device comprising: an elongated, resiliently bendable arm having a proximal longitudinal end and a distal longitudinal end, the arm being resiliently deformable about a bending direction; a hammer tip attached to the distal end of said arm for mechanically impacting said workpiece; the method comprising imparting an angular velocity to the proximal longitudinal end of the arm by rotating the proximal longitudinal end about an actuator axis that is essentially parallel to the bending direction of the arm, the angular velocity following a predetermined angular velocity profile; The method, wherein the angular velocity profile is configured to impart an instantaneous impact to the workpiece.

8. 8. The method of claim 7, wherein the angular velocity profile includes a pivot point at which the angular velocity imparted to the distal longitudinal end of the arm changes sign, the pivot point being earlier than the impact on the workpiece.

9. 9. The method of claim 7 or 8, wherein the workpiece is a 3D printed workpiece.

10. The method of claim 9 , wherein the workpiece is made from metal.

11. An impact device kit for mounting the impact device according to claim 1 or 2, a set of elongate elastic bendable arms, each bendable arm being elastically deformable about a bending direction, said bendable arms having a proximal longitudinal end and a distal longitudinal end; a set of hammer tips for mechanically impacting the workpiece, each of said hammer tips being attachable, and preferably attached, to the distal end of an arm of said set of elongated, resiliently bendable arms; - a programmable actuator interchangeably mountable to the longitudinal proximal end of each of said arms; wherein the actuator, when attached to the proximal longitudinal end of the working arm, is programmed to impart an angular velocity to the proximal longitudinal end of the working arm by rotating the proximal longitudinal end about an actuator axis that is essentially parallel to the bending direction of the working arm, the angular velocity following a predetermined angular velocity profile; The angular velocity profile is configured to impart an instantaneous impact to the workpiece.

12. 1. An impact excitation (IE) measurement system for measuring the vibration response of a workpiece to an instantaneous impact, comprising: - an impact device according to claim 1; a response recording device for capturing the vibration response of said workpiece to said momentary impact; a control unit for controlling the actuators of said impact device and said response recording device; a support device for holding said workpiece in place; A system comprising:

13. 1. An impact excitation (IE) measurement method for measuring the vibration response of a workpiece to an instantaneous impact, comprising: - supporting the workpiece in place; - applying a momentary impact to a workpiece according to the impact application method of claim 7 or 8; - capturing the vibration response of the workpiece to the instantaneous impact; whereby the vibration response of the workpiece to the instantaneous impact is measured.

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