Abstract:
A vibration-isolating pallet and method of construction thereof are presented. A load bearing platform is oriented along a horizontal plane to form a substantially level upper surface that can be configured to receive a load. A base is oriented under the load bearing platform and along the horizontal plane to form a lower surface that can be configured to maintain a stationary position when placed on a level surface. A suspension system is fixedly interposed between the load bearing platform and the base. The suspension system is structured to allow relative motion between the load bearing platform and the base.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates in general to pallets and, in particular, to a vibration-isolating pallet and method of construction thereof.  
       BACKGROUND OF THE INVENTION  
       [0002]     Intermodal shipping is used throughout the industrialized world to efficiently and securely transport freight. Intermodal shipping involves the use of more than one mode of transportation, including rail, ocean carrier, aircraft, and trucks, without any handling of the freight when changing transportation modes. Thus, intermodal shipping provides faster freight transport, while reducing damage and shipping loss through improved cargo handling.  
         [0003]     Pallets are widely used in intermodal shipping to provide flat transport structures to support goods while in transit in a stable and highly mobile fashion. Pallets are generally constructed of wood or other materials to provide a simple and low-cost structure that is generally considered disposable, although pallets constructed from plastics or high durability materials are intended for reuse. An ISO standardized pallet is approximately 40 inches wide by 48 inches deep by 5 inches high and is generally configured for two-way and four-way lifting using forklift-type devices. Other standardized and custom-sized pallets are also in use.  
         [0004]     Increasing reliance on intermodal shipping has resulted in greater losses due to goods damaged in transit. A pallet must provide stability necessary to withstand severe shifting and the breakup of stacks during transit. Palletized loads, however, are susceptible to damage from loss of pallet stack unitization. Generally, a pallet is stacked with multiple layers of individual cartons or units of goods. Higher pallet stacks help reduce transportation costs through efficient pallet and space utilization. Fuel costs, time, and competitive forces compel manufacturers to maximize palletized loads for optimal space utilization, yet increased load sizes increases the potential for damage. Moreover, the costs of damaged and lost goods are now charged back to the manufacturer, who is faced with the problem of balancing the risks for expected losses against efficiencies gained through maximizing load out.  
         [0005]     Vibration and the natural response frequencies of pallets are principal sources of damage to goods in transit, such as described in P.G. Reinhall and R. Carstens, “Achieving Effective Pallet Stack Unitization in Intermodal Shipping,” pp. 30-36, Packaging Tech. and Engr. (Apr. 1998), the disclosure of which is incorporated by reference. Freight is subjected to vibrations from the shipping means as an artifact of movement. Although shipping vibration forces are exerted three dimensionally, lateral vibrations are frequently more pronounced than longitudinal and vertical forces. Pallet natural frequencies are inherent to pallet structure, but resonance can vary based on the load height and weight. Overlaps of the resonance peak of a loaded pallet with peaks in the frequency spectra of shipping vibrations can cause potentially destructive resonance that can lead to loss of load integrity and subsequent damage to goods.  
         [0006]     Currently, pallet stacks can be strengthened to increase resilience to compromise while in transit. For example, shrink wrap, liquid cohesives, and column stacking can be used to unitize and strengthen pallet stacks and to lessen the occurrence of pallet stack failure. However, these unitization techniques are costly in terms of time, expense, and convenience and must frequently be tailored for a particular load configuration.  
         [0007]     Therefore, there is a need for a vibration-isolating pallet with a natural frequency substantially non-overlapping with transient variable shipping vibration peaks in power spectra. Preferably, such a pallet could be constructed at low cost, while be capable of anti-vibration tuning in one to three dimensions.  
       SUMMARY OF THE INVENTION  
       [0008]     A pallet with tunable natural frequency properties and method for construction thereof are provided. The pallet includes one or more medial support members fixedly interposed as a tunable suspension system between a top load bearing layer and a bottom base layer. Each tunable medial support member is constructed from materials to form a composite component that exhibits orthotropic properties to allow relative motion between the top load bearing layer and the bottom base layer. The selection of materials in each medial support and arrangement of medial support members between the top and bottom layers facilitates tuning of the resonance peak of the pallet under load and, in particular, tuning of response to shipping vibrations occurring maximally at peaks in lateral power spectra due to the shipping means.  
         [0009]     One embodiment provides a vibration-isolating pallet and method of construction thereof. A load bearing platform is oriented along a horizontal plane to form a substantially level upper surface that can be configured to receive a load. A base is oriented under the load bearing platform and along the horizontal plane to form a lower surface that can be configured to maintain a stationary position when placed on a level surface. A suspension system is fixedly interposed between the load bearing platform and the base. The suspension system is structured to allow relative motion between the load bearing platform and the base.  
         [0010]     Still other embodiments of the invention will become readily apparent to those skilled in the art from the following detailed description, wherein are described embodiments of the invention by way of illustrating the best mode contemplated for carrying out the invention. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications in various obvious respects, all without departing from the spirit and the scope of the invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a perspective view showing, by way of example, a prior art pallet laden with a stacked load.  
         [0012]      FIG. 2  is an exploded perspective view showing the prior art pallet of  FIG. 1 .  
         [0013]      FIG. 3  is a graph showing, by way of example, a frequency response curve for measured intermodal shipping vibration.  
         [0014]      FIG. 4  is a graph showing, by way of example, a frequency response curve for a prior art pallet laden with a stacked load.  
         [0015]      FIG. 5  is a perspective view showing a medial support member for use in the prior art pallet of  FIG. 1 .  
         [0016]      FIG. 6  is a transverse cross-sectional view showing the medial support member of  FIG. 5 .  
         [0017]      FIG. 7  is a perspective view showing a vibration-isolating pallet, in accordance with one embodiment.  
         [0018]      FIG. 8  is an exploded perspective view showing the vibration-isolating pallet of  FIG. 7 .  
         [0019]      FIG. 9  is a graph showing, by way of example, a frequency response curve for a vibration-isolating pallet laden with a stacked load.  
         [0020]      FIG. 10  is a perspective view showing a medial support member for use in the vibration-isolating pallet of  FIG. 7 .  
         [0021]      FIG. 11  is a transverse cross-sectional view showing the medial support member of  FIG. 10  at rest.  
         [0022]      FIG. 12  is a transverse cross-sectional view showing the medial support member of  FIG. 10  under load.  
         [0023]      FIG. 13  is a transverse cross-sectional view showing a medial support member with a single compressible layer, in accordance with a further embodiment.  
         [0024]      FIGS. 14-15  are transverse cross-sectional views showing medial support members with rollable support layers, in accordance with further embodiments.  
         [0025]      FIGS. 16-17  are side views respectively showing a pallet at rest and under lateral load that is constructed with the medial support member with rollable support layer of  FIG. 15 .  
         [0026]      FIG. 18  is a transverse cross-sectional view showing a medial support member with a combination of compressible and incompressible layers, in accordance with a further embodiment.  
         [0027]      FIGS. 19-20  are side views respectively showing a pallet at rest and under lateral load that is constructed with the medial support member with combination compressible layers of  FIG. 18 .  
         [0028]      FIG. 21  is a top view showing an arrangement of medial support members for use in the vibration-isolating pallet of  FIG. 7 .  
         [0029]      FIGS. 22-23  are top views respectively showing arrangements of medial support members for use in vibration-isolating pallets, in accordance with further embodiments. 
     
    
     DETAILED DESCRIPTION  
       [0000]     Prior Art Pallet Construction  
         [0030]     Pallets have become a ubiquitous element of intermodal shipping.  FIG. 1  is a perspective view  10  showing, by way of example, a prior art pallet  11  laden with a stacked load  12 . By way of example, the prior art pallet  11  is constructed of wood or other highly-available, low-cost materials to provide a stable and flat shipping platform. Individual cartons or units of goods  13  are stacked into one or more layers to form a load  12 . The pallet  11  and stacked load  12  must together exhibit stability sufficient to withstand vibrational forces exerted during transit, as further described below with reference to  FIGS. 3 and 4 .  
         [0031]     Although the dimensions of pallets are fairly standardized, the selection and arrangement of the individual components that together form a pallet can vary.  FIG. 2  is an exploded perspective view  20  showing the prior art pallet  11  of  FIG. 1 . Generally, the pallet  11  includes a load bearing layer  21 , medial support layer  23 , and base layer  24 . In addition, a medial cross-support layer  21  can be interposed between the load bearing and medial support layers. Other layers either in lieu of or in addition to the foregoing layers are possible.  
         [0032]     More particularly, the load bearing layer  21  includes one or more wood or framing members  25  that form a flat upper surface upon which a stacked load  12  can be placed. The medial support layer  23  includes one or more medial support members  27   a - i  that are fixed to the lower surface of the load bearing layer  21  or, if provided, medial cross-support layer  22 . Preferably, the medial support members  27   a - i  are arranged to facilitate the lifting of the pallet by a forklift-type device in two-way longitudinal or four-way longitudinal and lateral directions. Each medial support member  27   a - i  preferably includes a single block of wood, which provides the spacing necessary to accommodate lifting, as further described below with reference to  FIGS. 5 and 6 . The base layer  24  includes one or more wood or framing members  28   a - c  that are fixed to a lower surface of one or more of the medial cross members  27   a - i  to increase structural rigidity and to preserve the bottom surfaces of the individual medial cross members  27   a - i . Finally, the optional medial cross-support layer  22  includes one or more wood or framing members  26   a - c  that are fixed between the lower surface of the load bearing layer  21  and the upper surfaces of one or more of the medial support members  27   a - i  to provide cross support to the pallet in, for instance, a longitudinal or lateral direction. Other components, materials, and arrangements of elements are possible.  
         [0000]     Frequency Response Curves  
         [0033]     Goods in transit are generally subjected to vibrations while in transit that are exerted in three dimensions.  FIG. 3  is a graph  30  showing, by way of example, a frequency response curve  33  for measured intermodal shipping vibration. The x-axis  31  represents shipping vibration frequency measured in Hertz (Hz). The y-axis  32  represents energy measured as acceleration power spectral density (G 2 /Hz). The average lateral power spectrums of measured rail and truck portions of intermodal shipping vibrations are represented by the frequency response curve  33 .  
         [0034]     The energy of motion due to vibration is distributed primarily between 2.0 Hz and 6.0 Hz for rail transportation and between 15.0 Hz and 23.0 Hz for truck transportation. Excitation of the lowest lateral mode of a stacked load  12  generally occurs during rail transportation with a peak in frequency spectra  34  due to shipping vibration occurring at about 4.0 Hz.  
         [0035]     Although significant peak accelerations due to intermodal shipping vibrations occur along all three dimensions, the lateral movement of a stacked load  12  sufficient to cause high box-to-box interface stress and slippage will most likely result in failure. The amplitude of peak accelerations only becomes large if an input vibration contains significant energy and frequencies to which the stacked load  12  is sensitive. An indirect measure of total energy of input vibration to a stacked load  12  is the root mean square (RMS) of wood pallet acceleration. Empirically, longitudinal vibration RMS is lower than the vibration RMS exhibited in vertical and transverse directions and lateral vibration RMS is comparable to vertical vibration RMS. Id.  
         [0036]     The natural frequencies of a pallet  11  can affect the stability of a stacked load  12  to a significant degree.  FIG. 4  is a graph  40  showing, by way of example, a frequency response curve  43  for a prior art pallet laden  11  with a stacked load  12 . The x-axis  41  represents frequency measured in Hertz (Hz). The y-axis  42  represents transmissibility. The frequency response curve  43  reflects the natural frequencies of a stacked load  12 , which can be influenced by parameters that include stack geometry, box or container stiffness, and stack weight. A resonant peak  44  occurs at about 4.0 Hz. Other parameters can influence natural pallet frequency.  
         [0037]     Shipping vibrations become particularly destructive when a peak in power spectra overlaps with a resonant peak in frequency response for a stacked load  12 . Overlaps can cause unacceptably high response levels in the stacked load  12 , even when RMS is moderate. Empirically, vertical shipping vibrations exhibit the most energy in the frequency range of 10.0 Hz to 13.0 Hz, within which a loaded stack  12  exhibits a high natural frequency. A pallet  11  is most insensitive to vertical shipping vibrations. Thus, a destructive resonant situation is avoided. Lateral shipping vibrations, though, exhibit maximum energy distributed over a wider frequency range than vertical motion. A significant overlap of frequency resonance peaks for stacked loads  12  and the lowest frequency peaks in power spectra due to lateral shipping vibrations occurs in the 1.5 Hz to 3.75 Hz range. Consequently, lateral shipping vibrations impart significant motion to a stacked load  12  due to resonance phenomena that can potentially lead to lateral destruction of the stack. The frequencies corresponding to shipping vibration peaks are dependent on various parameters that include the mode of transportation, gross weight of the transporting vehicle, and the speed of travel. Other parameters are possible. Fine tuning the location of the natural frequency of a stacked load  12  to avoid shipping vibration peaks is difficult due to the variability of shipping vibration peaks.  
         [0000]     Prior Art Medial Support Member  
         [0038]     Structurally, the medial support members  27   a - i  most strongly influence natural frequency response.  FIG. 5  is a perspective view  50  showing a medial support member  27   a  for use in the prior art pallet  11  of  FIG. 1 . Conventionally, each medial support member  27   a  is typically constructed from a single block of wood or similar high density material. The lateral support member  27   a  must have sufficient structural strength to bear a proportionate share of the overall load for which the pallet is maximally rated.  
         [0039]     The primary consideration in determining the materials used to construct each medial support member  27   a  and the arrangement of the medial support members  27   a - i  within a pallet  11  are dictated by load bearing considerations and not with fine tuning natural frequency response. Generally, each medial support member  27   a  is composed from isotropic materials that exhibit the same mechanical properties in all directions.  FIG. 6  is a transverse cross-sectional view  60  showing the medial support member  27   a  of  FIG. 5 . The height  62  of each medial support member  27   a  is a function of overall pallet height, while the width  63  of each medial support member  27   a  is selected to facilitate lifting of the pallet  11  with a forklift-type device. For two-way pallets, a width  63  is selected to allow longitudinal insertion of forklift tines, while the depth (not shown) can be co-extensive with the overall depth of the load bearing platform layer  21  (shown in  FIG. 2 ). For four-way pallets, width  63  and depth are both selected to facilitate longitudinal insertion of forklift tines.  
         [0040]     Each medial support member  27   a  is rigid and relatively unyielding in lateral directions  65  in response to forces applied in the vertical directions  64 , such as due to the loading of a stacked load  12 . As a result, each medial support member  27   a  efficiently transmits lateral shipping vibration energy onto the stacked load  12 , thereby exposing the stacked load  12  to potentially destructive lateral resonance.  
         [0000]     Vibration-Isolating Pallet Construction  
         [0041]     A pallet and method for construction thereof can be provided with natural frequency properties adjustable through orthotropic medial support members that form a tunable suspension system.  FIG. 7  is a perspective view  70  showing a vibration-isolating pallet  71 , in accordance with one embodiment. By way of example, the majority of the pallet  71  is constructed of wood or other highly-available, low-cost materials to provide a stable and flat shipping platform. Individual cartons or units of goods  13  are stacked into one or more layers to form a load  72  and the combined natural frequencies of the pallet  11  and stacked load  72  can be tuned to resist peak frequencies in power spectra, as further described below with reference to  FIG. 9 .  
         [0042]     The medial support members are tunable to facilitate tuning of the resonance peak of a pallet under load and, in particular, tuning of response to shipping vibrations occurring maximally at peaks in lateral power spectra due to the shipping means.  FIG. 8  is an exploded perspective view  80  showing the vibration-isolating pallet  71  of  FIG. 7 . Generally, the pallet  71  includes a load bearing layer  81 , medial support layer  83 , and base layer  84 . In addition, a medial cross-support layer  81  can be interposed between the load bearing and medial support layers. Other layers. either in lieu of or in addition to the foregoing layers are possible.  
         [0043]     More particularly, the load bearing layer  81  includes one or more wood or framing members  85  that form a flat upper surface upon which a stacked load  72  can be placed. The medial support layer  83  includes one or more tunable medial support members  87   a - i  that are fixed to the lower surface of the load bearing layer  81  or, if provided, medial cross-support layer  82 . The medial support members  87   a - i  form a suspension system that is structured to allow relative motion between the load bearing and base layers.  
         [0044]     Preferably, the medial support members  87   a - i  are arranged to facilitate the lifting of the pallet by a forklift-type device in two-way longitudinal or four-way longitudinal and lateral directions. Each medial support member  87   a - i  is constructed as a composite of component materials, or as a unitary structure similar structural properties, as further described below with reference to  FIG. 10  et seq. The base layer  84  includes one or more wood or framing members  88   a - c  that are fixed to a lower surface of one or more of the medial cross members  87   a - i  to increase structural rigidity and to preserve the bottom surfaces of the individual medial cross members  87   a - i . Finally, the optional medial cross-support layer  82  includes one or more wood or framing members  86   a - c  that are fixed between the lower surface of the load bearing layer  81  and the upper surfaces of one or more of the medial support members  87   a - i  to provide cross support to the pallet in, for instance, a longitudinal or lateral direction. Other components, materials, and arrangements of elements are possible.  
         [0000]     Frequency Response Curve  
         [0045]     The medial support members  87   a - i  allow the resonance peaks of the stacked load  72  to be tunably shifted.  FIG. 9  is a graph  90  showing, by way of example, a frequency response curve  93  for a vibration-isolating pallet  71  laden with a stacked load  72 . The x-axis  91  represents frequency measured in Hertz (Hz). The y-axis  92  represents transmissibility. The frequency response curve  93  reflects the natural frequencies of a stacked load  12 , which can be influenced by parameters that include stack geometry, box or container stiffness, and stack weight. Other parameters can influence natural pallet frequency.  
         [0046]     The natural frequencies of the stacked load  72  have been shifted by tuning the tunable medial support members  87   a - i  that constitute the suspension system. The suspension system is tuned such that vertical stiffness exceeds one or both of lateral and longitudinal stiffness. In addition, the suspension system can be further tuned such that lateral and longitudinal stiffness are substantially equal. By way of example, the resonance peak  95  has been shifted to occur around 8.0 Hz and thereby avoids overlapping the lowest frequency peak  94  in the power spectra of lateral shipping vibrations that occurs at about 4.0 Hz. The shifting of the pallet natural frequency allows improved resilience to potentially destructive resonance, which would otherwise occur due to overlap.  
         [0047]     In one embodiment, the lateral, longitudinal, and lateral stiffness of the suspension system are tuned such that the lowest combined natural frequencies of the pallet  71  and load  72  are less than a lowest peak frequency in power spectrum of the shipping vibration. In a further embodiment, vertical, longitudinal, and lateral suspension system stiffness are tuned such that the combined natural frequencies of the pallet  71  and load  72  occurring at a frequency that is lower than 2.0 KHz do not coincide with peak frequencies in power spectrum of the shipping vibration. Other stiffness tunings are possible.  
         [0000]     Vibration-Isolating Medial Support Member Construction  
         [0048]     Each tunable medial support member  87   a  is constructed as a composite of component materials, or as a unitary structure exhibiting similar structural properties.  FIG. 10  is a perspective view  100  showing a medial support member  87   a  for use in the vibration-isolating pallet  71  of  FIG. 7 . In one embodiment, each tunable medial support member  87   a  is fashioned in a plurality of layers, although a single layer could also be employed, provided the appropriate orthotropic properties were exhibited, as further described below with reference to  FIGS. 11 and 12 . The materials used in each layer are selected by density, compressibility, and flexibility and are sized and arranged to shift the resonance peaks of the loaded stack  72 . For example, a compressible middle layer  102  could be fixedly interposed between a relatively incompressible top layer  101  and bottom layer  103 . The resulting tunable medial support member  87   a  accommodates stack geometry, box, or container stiffness, and load weight, as well as other parameters that can influence pallet natural frequencies.  
         [0049]     Each of the tunable medial support members  87   a - i  is constructed from materials to form a composite component that exhibits orthotropic properties to allow or limit relative lateral, longitudinal, and vertical motion between the load bearing and base layers.  FIG. 11  is a transverse cross-sectional view  100  showing the medial support member  87   a  of  FIG. 10  at rest. In one embodiment, each medial support member  87   a  provides some combination of lateral, longitudinal, and vertical flexibility or stiffness. Each medial support member  87   a  can be fabricated from a non-uniform buildup of a material, preferably using a material that is compressible and which is formed into at least one layer. Additionally, each medial support member  87   a  can further be fabricated with at least one layer of rigid material. Thus, the middle layer  112  can be constructed from compressible materials, such as rubber, foam, silicon, and similar materials, or could be a contained volume that overall provides an orthotropic effect, such as a rubber or elastic bladder filled with an incompressible gas or fluid or a compliant solid. Further, the top and bottom layers  112 ,  113  can be constructed from rigid materials, such as wood, plastic, metal, plywood, and so forth. Other compressible and rigid materials are possible. A width  115  is selected to facilitate two-way or four-way loading with forklift-type devices, while the height  114  is selected to adjust the height of the pallet while under load to a predetermined and standardized height.  
         [0050]     In one embodiment, the height  114  of each tunable medial support member  87   a  changes with the application of a stacked load, which exerts vertical forces  116  against the upper and lower layers  111 ,  113  that generates a response to lateral forces  117  in the middle layer  112 .  FIG. 12  is a transverse cross-sectional view  120  showing the medial support member  87   a  of  FIG. 10  under load. The height  121  of the tunable medial support member  87   a  has decreased proportionate to the vertical load forces  123  generated by the stacked load  72 . The middle layer  112  responds by compressing to a decreased vertical height  121  and by deforming outwardly  124  with a lateral offset  122  proportionate to the load weight.  
         [0051]     The amount of stiffness, flex, compression, and deformity can be tuned. The composite construction of rigid upper layer  111  and lower layer  112  and compressible middle layer  112  enable each of the medial support members  87   a - i  to impart shifted natural frequencies to the pallet  71 . In particular, lateral shipping vibration energy is resisted in part through the use of a compressible material for the medial support members  87   a - i  and by providing an orthotropic composite medial support member in place of rigid medial support members.  
         [0052]     Compression and deformity of the tunable medial support members  87   a - i  occur when a compressible material is used in the middle layer  112 . However, tunable medial support members that exhibit orthotropic properties can also be constructed using other materials or composite constructions. Several examples will now be discussed.  
         [0000]     Single Compressible Layer  
         [0053]     First, a single layer of compressible material could be used in the middle layer of each tunable medial support member.  FIG. 13  is a transverse cross-sectional view  139  showing a medial support member  131  with a single compressible layer  133 , in accordance with a further embodiment. Top layer  132  and bottom layer  134  are constructed from rigid materials. The middle layer  133  is constructed from a compressible material, such as wood or foam, that deforms sufficiently when stressed to alter the resonance peak of the pallet  71  under load.  
         [0000]     Rollable Support Layer  
         [0054]     Second, the tunable medial support members could be constructed without compressible materials.  FIGS. 14-15  are transverse cross-sectional views  140 ,  150  showing medial support members  141 ,  151  with rollable support layers  143 ,  153  in accordance with further embodiments. Referring first to  FIG. 14 , flexible members  142 ,  144  are oriented vertically and placed on opposite sides of a rollable support member  143 . The flexible members  142 ,  144  and rollable support member  143  need not be compressible. The flexible members  142 ,  144  must permit vertical flex and the rollable support member  143  is preferably solid. The rollable support member  143  is solid and has a generally ovaloid cross section to allow omnidirectional horizontal rotation when the pallet  71  under load experiences lateral or longitudinal motion.  
         [0055]     Referring next to  FIG. 15 , flexible members  152 ,  154  are similarly oriented vertically and placed on opposite sides of a rollable support member  153 . The flexible members  152 ,  154  and rollable support member  153  need not be compressible. The flexible members  152 ,  154  must permit vertical flex and the rollable support member  153  is preferably solid. The rollable support member  153  is hollow and has a generally circular cross section to allow unidirectional lateral rotation when the pallet  71  under load experiences shear. However, the rollable support member  153  resist vertical and longitudinal motion.  
         [0056]      FIGS. 16-17  are side views  160 ,  165  respectively showing a pallet  161  at rest and under lateral load that is constructed with the medial support member with rollable support layer  151  of  FIG. 15 . Referring first to  FIG. 16 , the rollable support members  153  provide vertical support to the load bearing layer and the load. Referring next to  FIG. 17 , the rollable support members  153  prevent significant vertical motion  186  when the base layer of the pallet experiences shear. The load bearing layer stays horizontal and significantly fixed in vertical orientation. The rollable support members  153  respectively roll along the bottom and top surfaces of the load bearing and base layers. Accordingly, the flexible members  152 ,  154  and rollable support members  153  provide lateral flexibility  187  in response to shear and flexing of the rollable support members  153  accommodate vertical motion  186  sufficient to alter the resonance peak of the pallet  71  under load.  
         [0000]     Combination Compressible Layer  
         [0057]     Finally, the composite could be a “sandwich” of alternating compressible and incompressible materials.  FIG. 18  is a transverse cross-sectional view  170  showing a medial support member  171  with a combination of compressible and incompressible layers  174   a - d ,  175   a - c , in accordance with a further embodiment. Alternating compressible and incompressible layers  174   a - d ,  175   a - c  are placed between a top layer  172  and bottom layer  173 . Each of the compressible layers  174   a - d  can be constructed from the same or different types of materials, with varying densities, thicknesses, and sizes. Similarly, each of the incompressible layers  175   a - c  can be constructed from the same or different types of materials, with varying densities, thicknesses, and sizes. In one embodiment, the compressible layers  174   a - d  are bonded to the top layer  172 , incompressible layers  174   a - c , and bottom layer  173 . The compressible layers  174   a - d  are made up of thin layers of rubber or silicon steel, plastic, or wood and the incompressible layers  175   a - c  are made up of steel, plastic, or wood. Other materials are possible. The combined layers form a sandwiched structure.  
         [0058]      FIGS. 19-20  are side views  180 ,  185  respectively showing a pallet  181  at rest and under lateral load that is constructed with the medial support member with a combination of compressible and incompressible layers  174   a - d ,  175   a - c  of  FIG. 18 . Referring first to  FIG. 19 , the sandwiched structure of the compressible and incompressible layers  174   a - d ,  175   a - c  provides vertical support to the load bearing layer and the load. Referring next to  FIG. 20 , the compressible and incompressible layers  174   a - d ,  175   a - c  prevent significant vertical motion  186  when the base layer of the pallet experiences shear. The load bearing layer stays horizontal and significantly fixed in vertical orientation. The compressible layers  174   a - d  distort horizontally. Accordingly, the compressible and incompressible layers  174   a - d  and top and bottom layers  172 ,  173  provide lateral flexibility  187  in response to shear and distortion of the compressible layers  174   a - d  accommodate vertical motion  187  sufficient to alter the resonance peak of the pallet  71  under load.  
         [0059]     The medial support members  131 ,  141 ,  151 ,  171  present the use of alternate composite components by way of illustration and are not meant to represent a comprehensive or limiting survey of possible materials or composite constructions. Other materials or composite constructions are possible.  
         [0000]     Vibration-Isolating Medial Support Member Arrangement  
         [0060]     The arrangement and placement of the tunable medial support members  87   a - i  between the load bearing layer  81 , or, if provided, medial cross-support layer  81 , and the base layer  84  can also be tuned to shift the resonance peaks of the loaded stack  72 . In addition, a  FIG. 21  is a top view  190  showing an arrangement  191  of medial support members  82   a - i  for use in the vibration-isolating pallet  71  of  FIG. 7 . By way of example, the medial support members  82   a - i  are arranged to facilitate the lifting of the pallet by a forklift-type device in four-way longitudinal and lateral directions. The medial support members  82   a - i  could also be arranged to facilitate the lifting of the pallet by a forklift-type device only in two-way longitudinal directions (not shown).  
         [0061]     The tunable medial support members  87   a - i  within the pallet  71  are arranged to provide stable support to the loaded stack  72  and to evenly distribute  191  load mass across the load bearing layer  81 . However, fewer, or more, tunable medial support members could be used to alter load mass distribution or to lower overall pallet cost, which may be particularly desirable when a low weight loaded stack  72  is expected.  FIGS. 22-23  are top views  195 ,  200  respectively showing arrangements  196 ,  201  of medial support members  198   a - d ,  203  for use in vibration-isolating pallets, in accordance with further embodiments.  
         [0062]     First, intermediate medial support members could be omitted. Referring to  FIG. 22 , tunable medial support members  198   a - d  are provided only at the corners of the pallet  197 . Alternatively, corner medial supports could be omitted. Referring next to  FIG. 23 , only a single tunable medial support member  203  is provided in the center of the pallet  202 . The respective arrangements of the tunable medial support members  198   a - d ,  203  allow the load mass to remain evenly distributed  196 ,  201 , even though intermediate and corner tunable medial support members are not used.  
         [0063]     The medial support members  82   a - i ,  198   a - d ,  203  present arrangements and placements by way of illustration and are not meant to represent a comprehensive or limiting survey of arrangements and placements. Other arrangements and placements are possible, including arrangements and placements of tunable medial support members and conventional solid medial support members, such as described above with reference to  FIGS. 5 and 6 .  
         [0064]     While the invention has been particularly shown and described as referenced to the embodiments thereof, those skilled in the art will understand that the foregoing and other changes in form and detail may be made therein without departing from the spirit and scope of the invention.