Damped instrument kinematic mounts

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to an attenuator kinematic mount.

【0002】

[Conventional technology]

In order to achieve propulsion weight efficiency for some space flight missions now and in the near future, spacecraft structures require the use of lightweight and robust advanced composites in their construction. Unfortunately, these lightweight composites, unlike bolted metal structures, have little inherent damping or vibration dissipation properties. Therefore, due to its light weight and low damping, many structural subsystems, including their instruments and electronic observation instruments, may be subject to dangerously high levels of vibration that impair their function. Of particular interest here are the instruments mounted on the precision kinematic mount (KM). Due to their structural techniques, these KMs have little inherent damping and therefore promote the vibrating environment of the instrument during flight. These environmental effects occur during powered flight and during the separation / separation of rocket injection equipment (pyrotechnic equipment). In fact, 14% of spacecraft launches (600 launches) up to 1984 have experienced vibration / shock related failures. Of these failures, 50% have failed missions that lead to catastrophe.

【0003】

Efforts are currently underway to form an improved version of the graphite structure that reduces the total vibration response level of the entire spacecraft structure. Tests and analyzes of numerous space programs using lightweight graphite composite structures show that the level of vibration reduction that is likely to be achieved is not sufficient to keep already developed instruments within their design levels. It shows that it may be sufficient. Therefore, if it becomes clear that the vibration reduction of the spacecraft structure is insufficient, it is necessary to confirm the development of additional vibration reduction technology for the instrument and prepare for it. In FIG. 1, instrument 10 is a rectangular solid represented by a broken line. Instrument 10 is supported by six small precision-polished flat pads 12, 14, 16, 18, 20, 22 that withstand only loads perpendicular to its plane (individually, these pads are bent). Can't withstand the moment). Under gravity, the three pads 12, 14, 16 support the weight of the instrument 10, that is, these pads exert a restraining force in the z direction. In addition, these pads prevent the instrument 10 from rotating along the x-axis and y-axis. Pads 18 and 20 prevent instrument 10 from translating along the y-axis and rotating along the z-axis. Finally, the pad 22 prevents the instrument 10 from translating along the x-axis.

【0004】

However, in practice, it is very difficult to construct a linear system of supports that suppresses only translation and not rotation (ie, bending action). Figures 2 to 4 show three types of kinematic mounts with conventional configurations. These three types of mounts are indicated by 24, 30, and 36, respectively, in FIGS. 2 to 4. These mounts contain a collection of bars 30, 32, 34, 38, 40, 42, 44 mounted together. Mount 24 (FIG. 2) is configured to hold the instrument axially, primarily along the longitudinal axis of the bar 30, as indicated by arrow 25. Notches 26, 28 are formed on the top and bottom of the bar 30 to mimic the behavior of the hinges, thereby minimizing lateral translation and restraint of rotation along the three axes. .. By the same method, mount 30 (FIG. 3) and mount 36 (FIG. 4) are configured to mainly suppress translation in two directions and translation in three directions, as indicated by arrows 31 and 37, respectively. The instrument is attached to the spacecraft via mounts 24, 30, 36 in a conventional arrangement. For certain instruments, special performance requirements may be considered that determine the maximum stiffness that additional restraints can have other than the six restraints required by an ideal kinematic mount.

【0005】

[Problems to be Solved by the Invention]

Kinematic mounts, as shown in Figure 2, have had limited success. Even though these mounts are configured to carry the launch load safely, these structures are not prepared to minimize the load transmitted to the instrument 10. In particular, in the 6 suspension mode adopted by the mount, it is expected that there will be little effect of vibration damping, thus increasing the flight load on the attached instrument 10.

【0006】

An object of the present invention is to provide a kinematic mount equipped with a novel damping function. Another object of the present invention is to provide a kinematic mount with a passive energy dissipation mechanism to protect the instrument from potentially damaging flight loads. An incidental object of the present invention is to provide a kinematic mount that can be integrated into an existing KM structure. A further object of the present invention is to provide a kinematic mounting configuration using six identical strut elements to significantly reduce manufacturing complexity and cost.

【0007】

Another object of the present invention is to slightly rearrange the 6-strut configuration to make the mount suspension mode nearly unconnected, thereby further enhancing the performance of the KM. Yet another object of the present invention is modal vibration for coupon sample mounts that results in a modal damping value of 5-17% of the critical damping, which provides a damping that is at least 1-2 orders of magnitude greater than in existing structures. The purpose is to provide a kinematic mount that enables testing.

【0008】

[Means for Solving the Invention]

These and other purposes include attenuating instrument support means having first and second damping means, the damping instrument kinetic mount in which the damping means and the instrument supporting means are arranged to provide the desired performance characteristics. Achieved by. Due to its general nature, this device can be applied to a large number of precision instruments or optics / sensors where alignment stability is important.

【0009】

BEST MODE FOR CARRYING OUT THE INVENTION

Kinematic mounts are widely used as base supports for precision optics and other high performance machinery. For space use, these mounts must meet two main requirements: 1) These mounts shall not adversely affect the stability of the instrument by mounting on a spacecraft structure that is less accurate than these mounts. 2) These mounts provide the instrument with a strong and stable support system during launch to minimize the load transmitted to the mounted instrument. The first requirement can be met if the mounting system suppresses only the six rigid body modes of the instrument and does not limit any other degree of freedom of movement of the instrument. This is equivalent to a statically determined mounting system that essentially isolates the instrument from non-ideal spacecraft interfaces and unpredictable moment loads due to differences in coefficient of thermal expansion.

【0010】

According to a preferred embodiment of the present invention, the kinematic mount is improved by inserting a vibration damping material into the mount. These damping materials introduce damping mechanisms into the six mount suspension modes, thereby causing heat dissipation and reducing high energy disturbances to the instrument. Improvements to the kinematic mount do not compromise essential features such as strength, stiffness and kinematic properties. Damping mechanisms can be provided at the machine-finished hinges or bending positions 26, 28, 32, 34, 38, 40, 42, 44 of the mount. In the case of the above six mount suspension modes, the most active part of the mount will be in these bending hinge positions. These relatively active areas can be utilized by configuring local dampers at these locations. This can be done in a number of ways and two embodiments of the damper structure are shown in FIGS. 5 and 6.

【0011】

The first embodiment of the damper structure can be confirmed in FIG. This embodiment uses a spherical damper 46 arranged around the bending region 62. The bending region 62 is formed by notches 26, 28 of the bar stock 30 used as the instrument support means 24. The spherical damper 46 is composed of two concentrically arranged partial shells 48 and 50. The first shell 48 is partly located above the second shell 50. The second shell 50 may have a solid structure. These two partial shells 48, 50 are a relatively soft layer of viscoelastic (VEM) damping material, one side bonded to the outer surface of the shell 50 and the other side bonded to the inner surface of the shell 48. Are connected to each other. Both partial shells have cylindrical extensions 54, 56 that are rigidly attached to the bar portion of the mount at positions 58, 60. Since the mount 46 deforms under a launch load, the mount 46 undergoes elastic rotation at both ends 26, 28 of the bar at the bending hinge position 62. Any bending action at the center of rotation 62 causes the damping viscoelastic layer 52 to actuate the spherical damper 46, thereby dissipating vibrational energy in the form of heat. By selecting an appropriate VEM52 with an appropriate shear coefficient, material loss coefficient and thickness, a significant level of damping can be achieved in the suspension vibration mode of the kinematic mount 46. In one embodiment, the two partial shells 48, 50 are made of titanium alloy. In its modified form, the two partial shells are non-metal.

【0012】

At first glance, it may seem that the addition of dampers adds unwanted bending stiffness to the mount 46 and impairs the proper kinematic mount function. However, it turns out that this is not the case. This is because the VEM properties are frequency (and temperature) dependent in a known way. At relatively high frequencies where suspension modal frequencies occur, the VEM shear modulus is relatively high, increasing the flexural rigidity applied to the mount 46, thereby dissipating the launch load. However, when in orbit where the action of a kinematic mount is required, thermal loads occur at very low load factors or frequencies. Typically, at these low frequencies, well below 1 Hertz, the VEM52's shear modulus is at least 20-30 (1/20-30) compared to the high frequency range. , Dramatically reduced. Therefore, the rigidity of the damper applied to the thermal load condition can be ignored as compared with the influence of the bending rigidity by the metal bending hinge 62. These new frequency-dependent properties of certain space-qualified VEM52s make the VEM52 a candidate for practical materials for damping kinematic mounts in flight.

【0013】

Figure 6 shows the modified form of the damper structure. This embodiment uses a cylindrical slot damper 66. The damper 66 uses a series of O-rings 68 arranged inside a plurality of slots 65. The O-ring is made of space-qualified, high-damping VEM. Slots 65 are arranged around the formed bending hinge 64. Instead of using a single bend hinge 62, a number of short bends are machined into the mount bar stock 64. The O-ring 68 receives a tensile or compressive force depending on the vibrating force applied to the instrument 10. Titanium alloys are commonly used to manufacture Mount 66 because of its light weight and high strength. Whereas the spherical damper described above works by causing shear deformation in the VEM, in the case of this structure it causes compression / tension in the VEM. As far as damping performance is concerned, the damping or loss coefficients of the material during compression / tension are the same as for shear. A closer look at Figure 6 reveals that VEM washers can be used instead of VEM O-rings. In each case, the difference in flexural rigidity characteristics is small enough to be applied.

【0014】

A series of flat washers 68 were modeled and analyzed. This model is for this prototype because each is 3.81 mm (0.15 inch) in length and a series of four aluminum pieces with a diameter of 7.9375 mm (0.3125 inch) (coupon samples are manufactured using aluminum). Includes a solid finite element model of a bend (of aluminum selected) and four VEM washers, each with a thickness of 0.508 mm (0.020 inch) and a diameter of 33.3375 mm (1.3125 inch). The analysis results show that in the case of a VEM washer made of 3M's ISD112 material, six suspension modes can be attenuated by as much as 10% of the critical modal attenuation. The 10% attenuation is at least an order of magnitude higher than the unmeasured mount. Therefore, the response of the random vibration evoked by the flight of the instrument 10 in these suspension modes will be approximately reduced to the square root of (1/10) or the level of 0.32 of the response by the unmeasured mount. Since the instrument receives only about 1/3 of the load in the high energy mount mode, it is considered to be a significant performance improvement compared to the configuration without damping measures.

【0015】

In the above section, we mentioned that there is an infinite arrangement of six suppressors for the kinematic mount (KM) to work. As long as the above object is achieved, another concept of damping KM structure may be used according to the present invention at the discretion. Truss structures can also be used due to their very good rigidity / weight ratio. As a variant, a set of three damping versions of the mount 30 shape shown in Figure 3 can also be used to provide the KM system. These can be arranged in various shapes on the base of instrument 10. The classical arrangement pattern is shown in Figure 7. In this figure, each of the six mount truss elements 74 is drawn as a line element for clarity. The damping bending hinge structures 46, 66 discussed in the previous sections (FIGS. 5 and 6) are similarly well applicable in this case as well. By analogy with the structure of FIG. 6, each of the six struts 74 shown in FIG. 7 can also take the form shown in FIG. Since all of the six bars 74 can be identical, the embodiments of FIGS. 8 and 9 can also use only a single strut structure. This is a major structural simplification, as each of the mount elements 30 and 36 can also be machined integrally from a metal block. In contrast, for the structures shown in FIGS. 8 and 9, only simple machining of standard bar blocks is required. In a preferred embodiment, the standard bar block can also be a titanium alloy.

【0016】

In addition to the simple structure of the mounting concept described above, the proposed mounting concept also has other advantages and desirable features. Instead of using the classic v shape as shown in Figure 7, arrange each pair of struts 30 so that the axial lines of action intersect at selected points inside the instrument 10. be able to. If the intersection of these three lines of action is chosen to be in the same horizontal plane as the center of mass of the instrument, the six suspension vibration modes of instrument 10 will be nearly unconnected. In addition to being a KM, this mounting mechanism constitutes a center of gravity mounting system. In applications where dynamic disturbances are inherent in the instrument, it is often important to obtain six nearly unconnected modes. For example, if the instrument induces a lateral imbalance force through its center of mass near the mount frequency, the instrument with the unconnected mode will only move laterally and of the instrument. It does not rotate the direction of the line of sight. Sure, not all instruments require this type of performance, however, if so, the proposed mounting mechanism provides this capability.

【0017】

The concept of the present invention is -Supporting means for instruments. -A strut that is connected to a support means to dampen vibrations, and this strut is composed of bar stock rather than an integral structure (monolithic). -Means for bending struts. The characteristic of attenuation is * Spherical * Cylindrical including. How the struts are formed, ie the "classical" arrangement; the structure for mounting.

【0018】

-Ideally a kinematic mount made of titanium.

【0019】

From the above description, it will be appreciated that the present invention makes it possible to protect the instrument from potentially damaging flight loads by using a dampening kinematic mount. Although the present invention has been described by exemplifying various embodiments, those skilled in the art will make various changes without departing from the true spirit and scope of the present invention, and the elements thereof will be equivalent. It will be understood that it can be replaced by a thing.

[Simple explanation of drawings]

[Figure 1]

This is an example of a conventional kinematic mount arrangement.

[Figure 2]

This is an example of the structure of a conventional kinematic mount.

[Fig. 3]

This is an example of the structure of a conventional kinematic mount.

[Fig. 4]

This is an example of the structure of a conventional kinematic mount.

[Fig. 5]

It is sectional drawing of the structure of the damper by a preferable embodiment of this invention.

[Fig. 6]

It is a cross-sectional view of the structure of a damper according to another preferred embodiment of the present invention.

[Fig. 7]

This is an example of the arrangement pattern of the kinematic mount.

[Fig. 8]

FIG. 5 is a side view of a single strut according to a preferred embodiment of the present invention.

[Fig. 9]

FIG. 8 is a cross-sectional view of a single strut at line AA in FIG.

[Explanation of symbols]

10 Instruments 12 Precision-polished flat pad 14 Precision-polished flat pad 16 Precision-polished flat pad 18 Precision-polished flat pad 20 Precision-polished flat pad 22 Precision-polished flat pad 24 mount 25 arrow 26 notch 28 notch 30 mount 30 bars 31 arrow 32 bars 34 bar 36 mount 37 arrow 38 bar 40 bars 42 bar 44 bars 46 Bending area 48 partial shell 50 partial shell 52 Viscoelastic damping material layer 54 Cylindrical extension 56 Cylindrical extension 58 position 60 positions 62 Spherical damper 64 Bending hinge 65 slots 66 Cylindrical slot damper 68 O-ring 74 mount truss element