Shock test device

Abstract

The invention relates to an impact test device with an impact body (100) and with a deflectable holder (200), with a support surface for placing a test object (300) on a first surface (201) of the holder and with an impact surface for the impact body on a second surface (202) of the holder for transmitting a mechanical impulse to the holder and the test object.

Description

State of the art

[0001] The invention relates to a shock testing device.

[0002] For micromechanical devices with moving parts, there are technical requirements regarding drop robustness. If the MEMS device falls from a certain height to the ground, nothing may be damaged, resulting in impaired functionality. Various methods exist to experimentally demonstrate drop robustness on a MEMS product or to uncover potential weaknesses during the development phase.

[0003] One method that best tests the desired drop resistance is to drop the device from a defined height onto a hard surface (e.g., granite). This process can be repeated indefinitely. At the end, the device's functionality can be tested or microscopic examinations can be performed to verify its structural integrity. The disadvantage of this method, however, is that the orientation of the device upon impact cannot be controlled. Therefore, it is not possible to determine which shock directions the component is most sensitive to.

[0004] There are other test fixtures, such as a Hopkinson bar, that allow the component's orientation to be fixed. The device is mounted on a plate, and a shock body is catapulted onto the plate at a defined speed. The shock profile experienced by the device depends on the materials and the type of mounting and is not necessarily comparable to the shock profile in a drop test. Furthermore, the plate to which the device is mounted is excited to vibrate, which continues to pump energy into the MEMS device after the primary shock. This can lead to structural damage that is not caused by the initial shock and would not occur in a pure drop test. Object of the invention

[0005] The object of the invention The object of the invention is to provide a shock test device that simulates a drop test, whereby a certain orientation of the test object is ensured. Advantages of the invention

[0006] The invention relates to an impact test device with an impact body and with a deflectable holder, with a support surface for placing a test object on a first surface of the holder and with an impact surface for the impact body on a second surface of the holder for transmitting a mechanical impulse to the holder and the test object.

[0007] The basic idea of ​​the invention is to invert the drop test. This means that instead of a device falling to the ground at a certain initial velocity, a "base plate" impacts a stationary device at a certain initial velocity. This allows for a defined orientation of the component relative to the force of the shock.

[0008] The advantage of the invention is that the device can be aligned in a defined orientation, thus determining the direction of the shock and ensuring that the shock profile closely matches the drop test. It thus combines the advantages of both prior art methods without the corresponding disadvantages.

[0009] Advantageous embodiments of the invention can be found in the subclaims. drawing Fig. 1 schematically shows a shock test device according to the invention in a first embodiment. Fig. 2 schematically shows a shock test device according to the invention in a second embodiment. The Fig. 3 a and b show schematically the rocker of a shock test device according to the invention Fig. 2 in two further embodiments. Description of implementation examples

[0010] Fig. 1 schematically shows a shock test device according to the invention in a first embodiment.

[0011] The impact test device comprises an impact body 100 in the form of a base plate 110 and a deflectable holder 200 in the form of a flexible membrane 210, which is designed such that a support surface is present on a first surface 201 on the upper side of the membrane, onto which a test object 300 can be placed. On an opposite second side 202, the underside of the membrane, there is an impact surface for the base plate, so that the impact body can transmit a mechanical impulse to the membrane and the test object. For this purpose, the base plate is arranged on a guide element 400 in the form of two guide rails 410, movable in an impact direction 10. The test object can be, for example, a micromechanical device whose impact resistance is to be tested.

[0012] The test object is positioned on a thin, flexible membrane, such as a rubber blanket, in the desired orientation. The underlying base plate can be accelerated to a speed v0 and impacts the membrane and thus the test object from below. Various mechanisms are conceivable for driving the plate, such as the pre-tensioning and release of a spring or electromagnetic drives such as a linear synchronous motor or a Gauss cannon. The movement of the base plate can be controlled by the guide rails and intercepted by stopper 600 after the membrane and, with it, the test object have been impacted.

[0013] Such a shock test fixture is well suited for shock testing MEMS devices because of their low mass. If the mechanical damping properties of the membrane are negligible, then the impact of the plate moving at v0 with the stationary test object is equivalent to the impact of the test object falling onto the base plate at velocity v0. For an elastic collision, the velocity v is D , with which the test object is thrown upwards: vD=2v0mPmP+mD where m D the mass of the test object and m P is the mass of the plate. Since the mass of the base plate will be large compared to the mass of the test object, especially a micromechanical device (m P >> m D ) applies to the speed of the test object v D≈ 2v0. This means that the test object flies away at a speed greater than the speed of the impactor. This automatically ensures that the duration of contact between the floor plate and the test object is no longer than in a real drop test. Furthermore, this means that the details of how the floor plate movement is absorbed by the stoppers are not important as long as it occurs after the collision, since the test object is no longer in contact with the plate shortly after the collision.

[0014] After the collision, the test object flies vertically upwards and finally lands back on the membrane. This demonstrates another advantage of a soft membrane, as it cushions the landing gently, preventing another harsh shock that could damage the test object.

[0015] Fig. 2 schematically shows a shock test device according to the invention in a second embodiment. Similar to the first embodiment, the test object can again be placed with a defined orientation. However, now the membrane is replaced by a rocker 220 and the base plate with a hammer 120. The test device 300 is placed on the first surface 201 on a first arm of the rocker. The impact surface for the hammer is arranged on the second surface 202 on a second arm of the rocker. The rocker is mounted for rotation about a first axis of rotation 221. The hammer is also mounted for rotation about a second axis of rotation 121. The hammer is tensioned by means of a spring 520 or moment spring 510 or can fall in an impact direction 10 solely by the acceleration due to gravity. If the mechanism is triggered, the hammer strikes the rocker with a speed v0, which reacts with a rotation about the first axis of rotation 221 and thus catapults the test object 300 upwards. If the mass of the hammer is again m Hmuch larger than the mass of the test object m D (m H >> m D ) and the inertia of the rocker is negligible, the test object flies at twice the speed (v D ≈ 2v0). The acceleration profile and the speed of the test object can be adjusted using the lever arm ratio of the rocker. The rotation of the rocker 220 is limited by the stopper 600.

[0016] The Fig. 3 a and b show schematically the rocker of a shock test device according to the invention Fig. 2 in two further embodiments.

[0017] Fig. Figure 3a shows a design of a rocker 220 in which the position of the first rotational axis 221 can be changed by creating various holes or bearings in the rocker. This allows the length ratio of the first and second rocker arms, i.e., the lever arm ratio, to be changed.

[0018] Fig.Figure 3b shows a design of a rocker 220 with multiple recesses on the top of the first rocker arm. Each recess defines a first surface 201 on which the test object 300 can be optionally placed. By varying the positioning of the test object, the effective length of the first lever arm can be changed.

[0019] Accordingly, the effective length of the second arm can also be changed by adjusting the impact location of the hammer, i.e. the position of the second surface 202, differently. List of reference symbols 10 Direction of attack 100 impact bodies 110 base plate 120 hammers 121 second axis of rotation 200 deflectable holders 201 First page 202 Second page 210 Flexible Membran 220 rocker 221 first axis of rotation 222 recess 300 test objects 400 guide element 410 guide rail 420 rotation axis 510 moment spring 520 spring 600 stoppers

Claims

[1] Impact test device with an impact body (100) and with a deflectable holder (200), with a support surface for placing a test object (300) on a first surface (201) of the holder and with an impact surface for the impact body on a second surface (202) of the holder for transmitting a mechanical impulse to the holder and the test object. [2] Shock test device according to claim 1, characterized by that the impact body (100) is arranged on a guide element (400) so as to be movable in an impact direction (10). [3] Shock test device according to claim 1 or 2, characterized by that the deflectable holder (200) is designed as a flexible membrane (210), wherein the first surface (201) is arranged on an upper side and the second surface (202) is arranged on an underside of the membrane. [4] Shock test device according to claim 3, characterized by that the impact body (100) is designed as a base plate (110). [5] Shock test device according to claim 1 or 2, characterized by that the deflectable holder (200) is designed as a rocker (220), wherein the first surface (201) is arranged on a first arm of the rocker and the second surface (202) is arranged on a second arm of the rocker. [6] Shock test device according to claim 5, characterized by that the length and / or the effective length of the first arm and / or the second arm is designed to be variable. [7] Shock test device according to claim 5 or 6, characterized by that the impact body (100) is designed as a hammer (120) and the second surface (202) of the rocker (220) is designed as an impact surface for the hammer.

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